Standard rules

Annotation formatting¶

Multiple annotations should be on a separate line than the annotated declaration; annotations with parameters should each be on separate lines; annotations should be followed by a space

Ktlint Disallowed

// A single annotation (without parameters) is allowed on same line as annotated construct
@FunctionalInterface class FooBar {
    @JvmField var foo: String

    @Test fun bar() {}
}

// A class or function parameter may have a single annotation with parameter(s) on the same line
class Foo(
    @Path("fooId") val fooId: String,
    @NotNull("bar") bar: String,
)

// Multiple annotations (without parameters) are allowed on the same line
@Foo @Bar
class FooBar {
    @Foo @Bar
    var foo: String

    @Foo @Bar
    fun bar() {}
}

// An array of annotations (without parameters) is allowed on same line as annotated construct
@[Foo Bar] class FooBar2 {
    @[Foo Bar] var foo: String

    @[Foo Bar] fun bar() {}
}

// An annotation with parameter(s) is not allowed on same line as annotated construct
@Suppress("Unused") class FooBar {
    @Suppress("Unused") var foo: String
    @Suppress("Unused") fun bar() {}
}
// Multiple annotation on same line as annotated construct are not allowed
@Foo @Bar class FooBar {
    @Foo @Bar var foo: String
    @Foo @Bar fun bar() {}
}

Rule id: standard:annotation

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:annotation")

Enable rule via .editorconfig

ktlint_standard_annotation = enabled

Disable rule via .editorconfig

ktlint_standard_annotation = disabled

Binary expression wrapping¶

Wraps binary expression at the operator reference whenever the binary expression does not fit on the line. In case the binary expression is nested, the expression is evaluated from outside to inside. If the left and right hand sides of the binary expression, after wrapping, fit on a single line then the inner binary expressions will not be wrapped. If one or both inner binary expression still do not fit on a single after wrapping of the outer binary expression, then each of those inner binary expressions will be wrapped.

Ktlint Disallowed

fun foo() {
    // Assume that the last allowed character is
    // at the X character on the right                       X
    if ((leftHandSideExpression && rightHandSideExpression) ||
        (
            leftHandSideLongExpression &&
                rightHandSideExpression
        )
    ) {
        // do something
    }
}

fun foo() {
    // Assume that the last allowed character is
    // at the X character on the right                       X
    if ((leftHandSideExpression && rightHandSideExpression) ||
        (leftHandSideLongExpression && rightHandSideExpression)
    ) {
        // do something
    }
}

Rule id: standard:binary-expression-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:binary-expression-wrapping")

Enable rule via .editorconfig

ktlint_standard_binary-expression-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_binary-expression-wrapping = disabled

Blank line before declarations¶

Requires a blank line before any class or function declaration. No blank line is required between the class signature and the first declaration in the class. In a similar way, a blank line is required before any list of top level or class properties. No blank line is required before local properties or between consecutive properties.

Ktlint Disallowed

const val FOO_1 = "foo1"

class FooBar {
    val foo2 = "foo2"
    val foo3 = "foo3"

    fun bar1() {
        val foo4 = "foo4"
        val foo5 = "foo5"
    }

    fun bar2() = "bar"

    val foo6 = "foo3"
    val foo7 = "foo4"

    enum class Foo
}

const val FOO_1 = "foo1"

class FooBar {
    val foo2 = "foo2"
    val foo3 = "foo3"
    fun bar1() {
        val foo4 = "foo4"
        val foo5 = "foo5"
    }
    fun bar2() = "bar"
    val foo6 = "foo3"
    val foo7 = "foo4"
    enum class Foo
}

Rule id: standard:blank-line-before-declaration

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:blank-line-before-declaration")

Enable rule via .editorconfig

ktlint_standard_blank-line-before-declaration = enabled

Disable rule via .editorconfig

ktlint_standard_blank-line-before-declaration = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Block comment initial star alignment¶

Lines in a block comment which (exclusive the indentation) start with a * should have this * aligned with the * in the opening of the block comment.

Ktlint Disallowed

/*
 * This comment is formatted well.
 */

/*
      * This comment is not formatted well.
    */

Rule id: standard:block-comment-initial-star-alignment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:block-comment-initial-star-alignment")

Enable rule via .editorconfig

ktlint_standard_block-comment-initial-star-alignment = enabled

Disable rule via .editorconfig

ktlint_standard_block-comment-initial-star-alignment = disabled

Chain method continuation¶

In a multiline method chain, the chain operators (. or ?.) have to be aligned with each other.

Multiple chained methods on a single line are allowed as long as the maximum line length, and the maximum number of chain operators are not exceeded. Under certain conditions, it is allowed that the expression before the first and/or the expression after the last chain operator is a multiline expression.

The . in java.class is ignored when wrapping on chain operators.

Warning

A binary expression for which the left and/or right operand consist of a method chain are currently being ignored by this rule. Please reach out, if you can help to determine what the best strategy is to deal with such kind of expressions.

Ktlint Disallowed

val foo1 =
    listOf(1, 2, 3)
        .filter { it > 2 }!!
        .takeIf { it > 2 }
        .map {
            it * it
        }?.map {
            it * it
        }
val foo2 =
    listOf(1, 2, 3)
        .filter {
            it > 2
        }.map {
            2 * it
        }?.map {
            2 * it
        }
val foo3 =
    foo().bar().map {
        it.foobar()
    }
val foo4 =
    """
    Some text
    """.trimIndent().foo().bar()

val foo1 =
    listOf(1, 2, 3).
        filter { it > 2 }!!.
        takeIf { it > 2 }.
        map {
            it * it
        }?.
        map {
            it * it
        }
val foo2 =
    listOf(1, 2, 3)
        .filter {
            it > 2
        }
        .map {
            2 * it
        }
        ?.map {
            2 * it
        }
val foo3 = 
    foo()
    .bar().map {
        it.foobar()
    }
val foo4 =
    """
    Some text
    """.trimIndent().foo()
        .bar()

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_chain_method_rule_force_multiline_when_chain_operator_count_greater_or_equal_than` Force wrapping of chained methods in case an expression contains at least the specified number of chain operators. If a chained method contains nested expressions, the chain operators of the inner expression are not taken into account. Use value `unset` (default) to disable this setting.	4	4	4

Rule id: standard:chain-method-continuation

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:chain-method-continuation")

Enable rule via .editorconfig

ktlint_standard_chain-method-continuation = enabled

Disable rule via .editorconfig

ktlint_standard_chain-method-continuation = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Class signature¶

Rewrites the class signature to a consistent format respecting the .editorconfig property max_line_length if set. In the ktlint_official code style all class parameters are wrapped by default. Set .editorconfig property ktlint_class_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than to a value greater than 1 to allow classes with a few parameters to be placed on a single line. The other code styles allow an infinite amount of parameters on the same line (as long as the max_line_length is not exceeded) unless .editorconfig property ktlint_class_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than is set explicitly.

Ktlint (ktlint_official) Disallowed (ktlint_official) Ktlint (non ktlint_official) Disallowed (non ktlint_official)

// Assume that max_line_length is not exceeded when written as single line
class Foo0

class Foo1(
    a: Any,
)

class Foo2(
    a: Any,
    b: Any,
)

class Foo3(
    @Foo a: Any,
    b: Any,
    c: Any,
)

class Foo4(
    a: Any,
    b: Any,
    c: Any,
) : FooBar(a, c)

class Foo5 :
    FooBar(
        "bar1",
        "bar2",
    ) {
    // body
}

class Foo6(
    val bar1: Bar,
    val bar2: Bar,
) : FooBar(
        bar1,
        bar2,
    ) {
    // body
}

class Foo7(
    val bar1: Bar,
    val bar2: Bar,
) : FooBar(
        bar1,
        bar2,
    ),
    BarFoo1,
    BarFoo2 {
    // body
}

class Foo8
    constructor(
        val bar1: Bar,
        val bar2: Bar,
    ) : FooBar(bar1, bar2),
        BarFoo1,
        BarFoo2 {
        // body
    }

// Assume that max_line_length is not exceeded when written as single line
class Foo0()

class Foo1(a: Any)

class Foo2(a: Any, b: Any)

class Foo3(@Foo a: Any, b: Any, c: Any)

class Foo4(a: Any, b: Any, c: Any) : FooBar(a, c)

class Foo5 : FooBar(
    "bar1",
    "bar2",
) {
    // body
}

class Foo6(
    val bar1: Bar,
    val bar2: Bar,
) : FooBar(
    bar1,
    bar2,
) {
    // body
}

class Foo7(
    val bar1: Bar,
    val bar2: Bar,
) : FooBar(
    bar1,
    bar2,
),
    BarFoo1,
    BarFoo2 {
    // body
}

class Foo8
constructor(
    val bar1: Bar,
    val bar2: Bar,
) : FooBar(bar1, bar2),
    BarFoo1,
    BarFoo2 {
    // body
}

// Assume that the last allowed character is
// at the X character on the right           X
class Foo0

// Entire class signature does not fit on single line
class Foo1(
    aVeryLonggggggggggggggggggggggg: Any
)

// Entire class signature does fit on single line
class Foo2(a: Any)

// Entire class signature does not fit on single line
class Foo3(
    aVeryLonggggggggggggggg: Any,
    b: Any
)

// Entire class signature does fit on single line
class Foo4(a: Any, b: Any)

// Entire class signature does fit on single line
class Foo5(@Foo a: Any, b: Any, c: Any)

// Entire class signature does fit on single line
class Foo6(a: Any, b: Any, c: Any) :
    FooBar(a, c)

// Entire class signature (without constructor invocation) does fit on single line
class Foo7 :
    FooBar(
        "bar1",
        "bar2"
    ) {
    // body
}

// Entire class signature (without constructor invocation) does fit on single line
class Foo8(val bar1: Bar, val bar2: Bar) :
    FooBar(
        bar1,
        bar2
    ) {
    // body
}

// Entire class signature (without constructor invocation) does not fit on single line
class Foo9(
    val aVeryLonggggggggggggggg: Bar,
    val bar2: Bar
) : FooBar(
    bar1,
    bar2
) {
    // body
}

class Foo10(val bar1: Bar, val bar2: Bar) :
    FooBar(
        bar1,
        bar2
    ),
    BarFoo1,
    BarFoo2 {
    // body
}

class Foo11
constructor(
    val bar1: Bar,
    val bar2: Bar
) : FooBar(bar1, bar2),
    BarFoo1,
    BarFoo2 {
    // body
}

// Assume that the last allowed character is
// at the X character on the right           X
class Foo0()

class Foo6(a: Any, b: Any, c: Any) : FooBar(a, c)

// Entire class signature (without constructor invocation) does fit on single line
class Foo7 : FooBar(
    "bar1",
    "bar2",
) {
    // body
}

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_class_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than` Force wrapping of the parameters of the class signature in case it contains at least the specified number of parameters, even in case the entire class signature would fit on a single line. Use value `unset` to disable this setting.	1	`unset`	`unset`

Rule id: standard:class-signature

Warn

For code styles android_studio and intellij_idea this rule rewrites multiline class signature to a single line class signature in case the entire class signature fits on a single line by default. In case you want to leave it to the discretion of the developer to decider whether a single or a multiline class signature is used, please suppress or disable this rule.

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:class-signature")

Enable rule via .editorconfig

ktlint_standard_class-signature = enabled

Disable rule via .editorconfig

ktlint_standard_class-signature = disabled

Enum entry¶

Enum entry names should be uppercase underscore-separated or upper camel-case separated.

Ktlint Disallowed

enum class Bar {
    FOO,
    Foo,
    FOO_BAR,
    FooBar,
}

enum class Bar {
    foo,
    bAr,
    Foo_Bar,
}

Rule id: standard:enum-entry-name-case

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:enum-entry-name-case")

Enable rule via .editorconfig

ktlint_standard_enum-entry-name-case = enabled

Disable rule via .editorconfig

ktlint_standard_enum-entry-name-case = disabled

File name¶

A file containing only one visible (e.g. non-private) class, and visible declarations related to that class only, should be named according to that element. The same applies if the file does not contain a visible class but exactly one type alias or one object declaration. Otherwise, the PascalCase notation should be used.

Rule id: standard:filename

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:filename")

Enable rule via .editorconfig

ktlint_standard_filename = enabled

Disable rule via .editorconfig

ktlint_standard_filename = disabled

Final newline¶

Ensures consistent usage of a newline at the end of each file.

Configuration setting	ktlint_official	intellij_idea	android_studio
`insert_final_newline`	`true`	`true`	`true`

Rule id: standard:final-newline

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:final-newline")

Enable rule via .editorconfig

ktlint_standard_final-newline = enabled

Disable rule via .editorconfig

ktlint_standard_final-newline = disabled

Function expression body¶

Rewrites a function body only containing a return or throw expression to an expression body.

Note

If the function body contains a comment, it is not rewritten to an expression body.

Ktlint Disallowed

fun foo1() = "foo"

fun foo2(): String = "foo"

fun foo3(): Unit = throw IllegalArgumentException("some message")

fun foo4(): Foo = throw IllegalArgumentException("some message")

fun foo5() {
    return "foo" // some comment
}

fun foo6(): String {
    /* some comment */
    return "foo"
}

fun foo7() {
    throw IllegalArgumentException("some message")
    /* some comment */
}

fun foo8(): Foo {
    throw IllegalArgumentException("some message")
    // some comment
}

fun foo1() {
    return "foo"
}

fun foo2(): String {
    return "foo"
}

fun foo3() {
    throw IllegalArgumentException("some message")
}

fun foo4(): Foo {
    throw IllegalArgumentException("some message")
}

Rule id: standard:function-expression-body

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-expression-body")

Enable rule via .editorconfig

ktlint_standard_function-expression-body = enabled

Disable rule via .editorconfig

ktlint_standard_function-expression-body = disabled

Function literal¶

Enforces the parameters of a function literal and the arrow to be written on the same line as the opening brace if the maximum line length is not exceeded. In case the parameters are wrapped to multiple lines then this is respected.

If the function literal contains multiple parameters and at least one parameter other than the first parameter starts on a new line than all parameters and the arrow are wrapped to separate lines.

Ktlint Disallowed

val foobar1 = { foo + bar }
val foobar2 =
    {
        foo + bar
    }
val foobar3 =
    { foo: Foo ->
        foo.repeat(2)
    }
val foobar4 =
    { foo: Foo, bar: Bar ->
        foo + bar
    }
val foobar5 = { foo: Foo, bar: Bar -> foo + bar }
val foobar6 =
    {
            foo: Foo,
            bar: Bar,
        ->
        foo + bar
    }

// Assume that the last allowed character is
// at the X character on the right           X
val foobar7 =
    barrrrrrrrrrrrrr { 
          fooooooooooooooo: Foo
        ->
        foo.repeat(2)
    }

val foobar3 =
    {
        foo: Foo ->
        foo.repeat(2)
    }
val foobar6 =
    { foo: Foo,
      bar: Bar ->
        foo + bar
    }
// Assume that the last allowed character is
// at the X character on the right           X
val foobar7 =
    barrrrrrrrrrrrrr { fooooooooooooooo: Foo ->
        foo.repeat(2)
    }

Rule id: standard:function-literal

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-literal")

Enable rule via .editorconfig

ktlint_standard_function-literal = enabled

Disable rule via .editorconfig

ktlint_standard_function-literal = disabled

Function signature¶

Rewrites the function signature to a single line when possible (e.g. when not exceeding the max_line_length property) or a multiline signature otherwise.

Note

Wrapping of parameters is also influenced by the parameter-list-wrapping rule.

Ktlint Disallowed

// Assume that the last allowed character is
// at the X character on the right           X
fun foooooooo(
    a: Any,
    b: Any,
    c: Any,
): String {
    // body
}

// Assume that the last allowed character is
// at the X character on the right           X
fun bar(a: Any, b: Any, c: Any): String {
    // body
}

// When wrapping of body is set to 'default'.
// Assume that the last allowed character is
// at the X character on the right           X
fun f(a: Any, b: Any): String = "some-result"
    .uppercase()

// When wrapping of body is set to 'multiline'
// or 'always'.
// Assume that the last allowed character is
// at the X character on the right           X
fun f(a: Any, b: Any): String =
    "some-result"
        .uppercase()

// Assume that the last allowed character is
// at the X character on the right           X
fun foooooooo(a: Any, b: Any, c: Any): String {
    // body
}

// Assume that the last allowed character is
// at the X character on the right           X
fun bar(
    a: Any,
    b: Any,
    c: Any
): String {
    // body
}

// When wrapping of body is set to 'default'.
// Assume that the last allowed character is
// at the X character on the right           X
fun f(a: Any, b: Any): String =
    "some-result"
        .uppercase()

// When wrapping of body is set to 'multiline'
// or 'always'.
// Assume that the last allowed character is
// at the X character on the right           X
fun f(a: Any, b: Any): String = "some-result"
    .uppercase()

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_function_signature_body_expression_wrapping` Determines how to wrap the body of function in case it is an expression. Use `default` to wrap the body expression only when the first line of the expression does not fit on the same line as the function signature. Use `multiline` to force wrapping of body expressions that consists of multiple lines. Use `always` to force wrapping of body expression always.	`multiline`	`default`	`default`
`ktlint_function_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than` Forces a multiline function signature in case the function contains the specified minimum number of parameters even in case the function signature would fit on a single line. Use value `unset` (default) to disable this setting.	2	`unset`	`unset`

default multiline always

When ktlint_function_signature_body_expression_wrapping is set to default, the first line of a body expression is appended to the function signature as long as the max line length is not exceeded.

ktlint_function_signature_body_expression_wrapping=default

// Given that the function signature has to be written as a single line
// function signature and that the function has a multiline body expression
fun someFunction(a: Any, b: Any): String = "some-result"
    .uppercase()

// Given that the function signature has to be written as a multiline
// function signature and that the function has a multiline body expression
fun someFunction(
    a: Any,
    b: Any
): String = "some-result"
    .uppercase()

When ktlint_function_signature_body_expression_wrapping is set to multiline, the body expression starts on a separate line in case it is a multiline expression. A single line body expression is wrapped only when it does not fit on the same line as the function signature.

ktlint_function_signature_body_expression_wrapping=multiline

// Given that the function signature has to be written as a single line
// function signature and that the function has a single line body expression
// that fits on the same line as the function signature.
fun someFunction(a: Any, b: Any): String = "some-result".uppercase()

// Given that the function signature has to be written as a multiline
// function signature and that the function has a single line body expression
// that fits on the same line as the function signature.
fun someFunction(
    a: Any,
    b: Any
): String = "some-result".uppercase()

// Given that the function signature has to be written as a single line
// function signature and that the function has a multiline body expression
fun someFunction(a: Any, b: Any): String =
    "some-result"
         .uppercase()

// Given that the function signature has to be written as a multiline
// function signature and that the function has a multiline body expression
fun someFunction(
    a: Any,
    b: Any
): String =
    "some-result"
       .uppercase()

When ktlint_function_signature_body_expression_wrapping is set to always the body expression is always wrapped to a separate line.

ktlint_function_signature_body_expression_wrapping=always

// Given that the function signature has to be written as a single line
// function signature and that the function has a single line body expression
fun someFunction(a: Any, b: Any): String =
    "some-result".uppercase()

// Given that the function signature has to be written as a multiline
// function signature and that the function has a multiline body expression
fun functionWithAVeryLongName(
    a: Any,
    b: Any
): String =
    "some-result"
        .uppercase()

Rule id: standard:function-signature

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-signature")

Enable rule via .editorconfig

ktlint_standard_function-signature = enabled

Disable rule via .editorconfig

ktlint_standard_function-signature = disabled

Function type modifier spacing¶

Enforce a single whitespace between the modifier list and the function type.

Ktlint Disallowed

val foo: suspend () -> Unit = {}

suspend fun bar(baz: suspend () -> Unit) = baz()

val foo: suspend() -> Unit = {}

suspend fun bar(baz: suspend   () -> Unit) = baz()

Rule id: standard:function-type-modifier-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-type-modifier-spacing")

Enable rule via .editorconfig

ktlint_standard_function-type-modifier-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_function-type-modifier-spacing = disabled

If else bracing¶

If at least one branch of an if-else statement or an if-else-if statement is wrapped between curly braces then all branches should be wrapped between braces.

Ktlint Disallowed

fun foo(value: int) {
    if (value > 0) {
        doSomething()
    } else if (value < 0) {
        doSomethingElse()
    } else {
        doSomethingElse2()
    }
}

fun foo(value: int) {
    if (value > 0)
        doSomething()
    else if (value < 0) {
        doSomethingElse()
    } else
        doSomethingElse2()
}

Rule id: standard:if-else-bracing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:if-else-bracing")

Enable rule via .editorconfig

ktlint_standard_if-else-bracing = enabled

Disable rule via .editorconfig

ktlint_standard_if-else-bracing = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Import ordering¶

Ensures that imports are ordered consistently (see Import Layouts for configuration).

Ktlint Disallowed

import com.bar.Bar
import com.foo.Foo
import org.foo.bar.FooBar
import java.util.concurrent.ConcurrentHashMap

import com.bar.Bar
import java.util.concurrent.ConcurrentHashMap
import org.foo.bar.FooBar
import com.foo.Foo

Rule id: standard:import-ordering

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:import-ordering")

Enable rule via .editorconfig

ktlint_standard_import-ordering = enabled

Disable rule via .editorconfig

ktlint_standard_import-ordering = disabled

Indentation¶

Indentation formatting - respects .editorconfig indent_size with no continuation indent (see EditorConfig section for more).

Ktlint Disallowed

fun main() {
    foobar(
        a,
        b,
        c,
    )
}

fun main() {
    foobar(
          a,
          b,
          c,
          )
}

Note

This rule handles indentation for many different language constructs which can not be summarized with a few examples. See the unit tests for more details.

Configuration setting	ktlint_official	intellij_idea	android_studio
`indent_size` The size of an indentation level when `indent_style` is set to `space`. Use value `unset` to ignore indentation.	4	4	4
`indent_style` Style of indentation. Set this value to `space` or `tab`.	`space`	`space`	`space`

Rule id: standard:indent

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:indent")

Enable rule via .editorconfig

ktlint_standard_indent = enabled

Disable rule via .editorconfig

ktlint_standard_indent = disabled

Naming¶

Backing property naming¶

Allows property names to start with _ in case the property is a backing property. ktlint_official and android_studio code styles require the correlated property/function to be defined as public.

Ktlint Disallowed

class Bar {
    // Backing property
    private val _elementList = mutableListOf<Element>()
    val elementList: List<Element>
        get() = _elementList
}

class Bar {
    // Incomplete backing property as public property 'elementList1' is missing
    private val _elementList1 = mutableListOf<Element>()

    // Invalid backing property as '_elementList2' is not a private property
    val _elementList2 = mutableListOf<Element>()
    val elementList2: List<Element>
        get() = _elementList2
}

Rule id: standard:backing-property-naming

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:backing-property-naming")

Enable rule via .editorconfig

ktlint_standard_backing-property-naming = enabled

Disable rule via .editorconfig

ktlint_standard_backing-property-naming = disabled

Class naming¶

Enforce naming of class and objects.

Ktlint Ktlint JUnit Test Disallowed

class Foo

class Foo1

class `class` // Any keyword is allowed when wrapped between backticks

@Nested
inner class `Some descriptive class name` {
    @Test
    fun `Some descriptive test name`() {
        // do something
    }
}

class foo
class Foo_Bar
class `Some class in the production code`

Note

Functions in files which import a class from package org.junit.jupiter.api are considered to be test functions and are allowed to have a name specified between backticks and do not need to adhere to the normal naming convention. Although, the Kotlin coding conventions does not allow this explicitly for class identifiers, ktlint does allow it.

This rule can also be suppressed with the IntelliJ IDEA inspection suppression ClassName.

Rule id: standard:class-naming

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:class-naming")

Enable rule via .editorconfig

ktlint_standard_class-naming = enabled

Disable rule via .editorconfig

ktlint_standard_class-naming = disabled

Function naming¶

Enforce naming of function.

Ktlint Ktlint Test Disallowed

fun foo() {}

fun fooBar() {}

fun `fun`() {} // Any keyword is allowed when wrapped between backticks

@Test
fun `Some name`() {}

@Test
fun do_something() {}

fun Foo() {}
fun Foo_Bar() {}
fun `Some name`() {}
fun do_something() {}

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_function_naming_ignore_when_annotated_with` Ignore functions that are annotated with values in this setting. This value is a comma separated list of names without the '@' prefix.	`unset`	`unset`	`unset`

Note

When using Compose, you might want to configure the function-naming rule with .editorconfig property ktlint_function_naming_ignore_when_annotated_with=Composable. Furthermore, you can use a dedicated ktlint ruleset like Compose Rules for checking naming conventions for Composable functions.

Note

Functions in files which import a class from package io.kotest, junit.framework, kotlin.test, org.junit, or org.testng are considered to be test functions. Functions in such classes are allowed to have underscores in the name. Also, function names enclosed between backticks do not need to adhere to the normal naming convention.

This rule can also be suppressed with the IntelliJ IDEA inspection suppression FunctionName.

Rule id: standard:function-naming

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-naming")

Enable rule via .editorconfig

ktlint_standard_function-naming = enabled

Disable rule via .editorconfig

ktlint_standard_function-naming = disabled

Package name¶

Validates that the package name matches the regular expression [a-z][a-zA-Z\d]*(\.[a-z][a-zA-Z\d]*)*.

Ktlint Disallowed

package foo
package foo.bar

package Foo
package foo.Foo
package `foo bar`
package foo.`foo bar`

Rule id: standard:package-name

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:package-name")

Enable rule via .editorconfig

ktlint_standard_package-name = enabled

Disable rule via .editorconfig

ktlint_standard_package-name = disabled

Property naming¶

Enforce naming of property.

Note

This rule can not reliably detect all situations in which incorrect property naming is used. So it only detects in which it is certain that naming is incorrect.

Ktlint Disallowed

val foo1 = Foo() // In case developers want to tell that Foo is mutable
val FOO1 = Foo() // In case developers want to tell that Foo is deeply immutable

const val FOO_BAR = "FOO-BAR" // By definition deeply immutable

var foo2: Foo = Foo() // By definition not immutable

class Bar {
    val foo1 = "foo1" // Class properties always start with lowercase, const is not allowed

    const val FOO_BAR = "FOO-BAR" // By definition deeply immutable

    var foo2: Foo = Foo() // By definition not immutable

    // Backing property
    private val _elementList = mutableListOf<Element>()
    val elementList: List<Element>
        get() = _elementList

    companion object {
        val foo1 = Foo() // In case developer want to communicate that Foo is mutable
        val FOO1 = Foo() // In case developer want to communicate that Foo is deeply immutable
    }
}

var `package` = "foo" // Any keyword is allowed when wrapped between backticks

const val fooBar = "FOO-BAR" // By definition deeply immutable

var FOO2: Foo = Foo() // By definition not immutable

class Bar {
    val FOO_BAR = "FOO-BAR" // Class properties always start with lowercase, const is not allowed

    // Incomplete backing property as public property 'elementList1' is missing
    private val _elementList1 = mutableListOf<Element>()

    // Invalid backing property as '_elementList2' is not a private property
    val _elementList2 = mutableListOf<Element>()
    val elementList2: List<Element>
        get() = _elementList2
}

This rule is suppressed whenever the IntelliJ IDEA inspection suppression PropertyName, ConstPropertyName, ObjectPropertyName or PrivatePropertyName is used.

Rule id: standard:property-naming

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:property-naming")

Enable rule via .editorconfig

ktlint_standard_property-naming = enabled

Disable rule via .editorconfig

ktlint_standard_property-naming = disabled

No blank lines in list¶

Disallow blank lines to be used in lists before the first element, between elements, and after the last element.

Super type

Ktlint Disallowed

class FooBar :
    Foo,
    Bar {
    // body
}

class FooBar :

    Foo,

    Bar

{
    // body
}

Type argument list

Ktlint Disallowed

val foobar: FooBar<
    Foo,
    Bar,
    > = FooBar(Foo(), Bar())

val foobar: FooBar<

    Foo,

    Bar,

    > = FooBar(Foo(), Bar())

Type constraint list

Ktlint Disallowed

class BiAdapter<C : RecyclerView.ViewHolder, V1 : C, V2 : C, out A1, out A2>(
    val adapter1: A1,
    val adapter2: A2,
) : RecyclerView.Adapter<C>()
    where A1 : RecyclerView.Adapter<V1>, A1 : ComposableAdapter.ViewTypeProvider,
          A2 : RecyclerView.Adapter<V2>, A2 : ComposableAdapter.ViewTypeProvider {
    // body
}

class BiAdapter<C : RecyclerView.ViewHolder, V1 : C, V2 : C, out A1, out A2>(
    val adapter1: A1,
    val adapter2: A2
) : RecyclerView.Adapter<C>()
    where
          A1 : RecyclerView.Adapter<V1>, A1 : ComposableAdapter.ViewTypeProvider,

          A2 : RecyclerView.Adapter<V2>, A2 : ComposableAdapter.ViewTypeProvider
{
    // body
}

Type parameter list

Ktlint Disallowed

fun <
    Foo,
    Bar,
    > foobar()

fun <

    Foo,

    Bar,

    > foobar()

Value argument list

Ktlint Disallowed

val foobar =
    foobar(
        "foo",
        "bar",
    )

val foobar = 
    foobar(

      "foo",

      "bar",

  )

Value parameter list

Ktlint Disallowed

fun foobar(
    foo: String,
    bar: String,
)

fun foobar(

    foo: String,

    bar: String,

)

Rule id: standard:no-blank-line-in-list

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-blank-line-in-list")

Enable rule via .editorconfig

ktlint_standard_no-blank-line-in-list = enabled

Disable rule via .editorconfig

ktlint_standard_no-blank-line-in-list = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

No consecutive comments¶

Consecutive comments are disallowed in following cases: - Any mix of a consecutive kdoc, a block comment or an EOL comment unless separated by a blank line in between - Consecutive KDocs (even when separated by a blank line) - Consecutive block comments (even when separated by a blank line)

Consecutive EOL comments are always allowed as they are often used instead of a block comment.

Ktlint Disallowed

// An EOL comment
// may be followed by another EOL comment
val foo = "foo"

// Different comment types (including KDoc) may be consecutive ..

/*
 * ... but do need to be separated by a blank line ...
 */

/**
  * ... but a KDoc can not be followed by an EOL or a block comment or another KDoc
  */
fun bar() = "bar"

/*
 * Block comments can not be consecutive ...
 */
/*
 * ... even not when separated by a new line.
 */
val bar = "bar" 

/**
  * A KDoc can not be followed by a block comment or an EOL comment or another KDOC
  */

// ... even not when separated by a new line.

Rule id: standard:no-consecutive-comments

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-consecutive-comments")

Enable rule via .editorconfig

ktlint_standard_no-consecutive-comments = enabled

Disable rule via .editorconfig

ktlint_standard_no-consecutive-comments = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

No empty file¶

A kotlin (script) file should not be empty. It needs to contain at least one declaration. Files only contain a package and/or import statements are as of that disallowed.

Rule id: standard:no-empty-file

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-empty-file")

Enable rule via .editorconfig

ktlint_standard_no-empty-file = enabled

Disable rule via .editorconfig

ktlint_standard_no-empty-file = disabled

No empty first line at start in class body¶

Detect blank lines at start of a class body.

Ktlint Disallowed

class Foo {
    val foo = "foo"
}

class Foo {

    val foo = "foo"
}

Rule id: standard:no-empty-first-line-in-class-body

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-empty-first-line-in-class-body")

Enable rule via .editorconfig

ktlint_standard_no-empty-first-line-in-class-body = enabled

Disable rule via .editorconfig

ktlint_standard_no-empty-first-line-in-class-body = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

No single line block comment¶

A single line block comment should be replaced with an EOL comment when possible.

Ktlint Disallowed

/*
 * Some comment
 */
val foo = "foo" // Some comment
val foo = { /* no-op */ }

/* Some comment */
val foo = "foo" /* Some comment */

Rule id: standard:no-single-line-block-comment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-single-line-block-comment")

Enable rule via .editorconfig

ktlint_standard_no-single-line-block-comment = enabled

Disable rule via .editorconfig

ktlint_standard_no-single-line-block-comment = disabled

Ktlint-suppression rule¶

The ktlint-disable and ktlint-enable directives are no longer supported as of ktlint version 0.50.0. This rule migrates the directives to Suppress or SuppressWarnings annotations.

Identifiers in the @Suppress and @SuppressWarnings annotations to suppress ktlint rules are checked for validity and autocorrected when possible.

Ktlint Disallowed

@file:Suppress("ktlint:standard:no-wildcard-imports")

class FooBar {
    @Suppress("ktlint:standard:max-line-length")
    val foo = "some longggggggggggggggggggg text"

    fun bar() =
        @Suppress("ktlint:standard:no-multi-spaces")
        listOf(
            "1   One", 
            "10  Ten", 
            "100 Hundred", 
        )
}

/* ktlint-disable standard:no-wildcard-imports */

class FooBar {
    val foo = "some longggggggggggggggggggg text" // ktlint-disable standard:max-line-length

    fun bar() =
        listOf(
            /* ktlint-disable standard:no-multi-spaces */
            "1   One", 
            "10  Ten", 
            "100 Hundred", 
            /* ktlint-enable standard:no-multi-spaces */
        )
}

Rule id: standard:ktlint-suppression

Note

This rule cannot be suppressed via @Suppress or be disabled in the .editorconfig.

Max line length¶

Ensures that lines do not exceed the maximum length of a line. This rule does not apply in a number of situations. The .editorconfig property ktlint_ignore_back_ticked_identifier can be set to ignore identifiers which are enclosed in backticks, which for example is very useful when you want to allow longer names for unit tests.

Ktlint Disallowed

// Assume that the last allowed character is
// at the X character on the right           X
// Lines below are accepted although the max
// line length is exceeded.
package com.toooooooooooooooooooooooooooo.long
import com.tooooooooooooooooooooooooooooo.long

val foo1 =
    """
    fooooooooooooooooooooooooooooooooooooooooo
    """

val foo2 =
    "fooooooooooooooooooooooooooooooooooooooo"

@Test
fun `Test description which is toooooooooooo long`() {
}

// Assume that the last allowed character is
// at the X character on the right           X
val fooooooooooooooo = "fooooooooooooooooooooo"
val foo = "foo" + "ooooooooooooooooooooooooooo"
val foooooooooooooo = "foooooooooooooooooooo" // some comment

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_ignore_back_ticked_identifier` Defines whether the backticked identifier (``) should be ignored.	`false`	`false`	`false`
`max_line_length` Maximum length of a (regular) line.	140	`off`	`100`

Rule id: standard:max-line-length

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:max-line-length")

Enable rule via .editorconfig

ktlint_standard_max-line-length = enabled

Disable rule via .editorconfig

ktlint_standard_max-line-length = disabled

Modifier order¶

Consistent order of modifiers

Ktlint Disallowed

abstract class A {
    protected open val v = ""

    internal open suspend fun f(v: Any): Any = ""

    protected lateinit var lv: String
}

abstract class A {
    open protected val v = ""

    open suspend internal fun f(v: Any): Any = ""

    lateinit protected var lv: String
}

Rule id: standard:modifier-order

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:modifier-order")

Enable rule via .editorconfig

ktlint_standard_modifier-order = enabled

Disable rule via .editorconfig

ktlint_standard_modifier-order = disabled

Multiline if-else¶

Braces required for multiline if/else statements.

Ktlint Disallowed

val foo =
    if (true) {
        return 0
    } else {
        return 1
    }

val foo =
    if (true)
        return 0
    else
        return 1

Rule id: standard:multiline-if-else

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:multiline-if-else")

Enable rule via .editorconfig

ktlint_standard_multiline-if-else = enabled

Disable rule via .editorconfig

ktlint_standard_multiline-if-else = disabled

Multiline loop¶

Braces required for multiline for, while, and do statements.

Ktlint Disallowed

for (i in 1..10) {
    println(i)
}

for (i in 1..10)
    println(i)

Rule id: standard:multiline-loop

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:multiline-loop")

Enable rule via .editorconfig

ktlint_standard_multiline-loop = enabled

Disable rule via .editorconfig

ktlint_standard_multiline-loop = disabled

No blank lines before `}`¶

No blank lines before }.

Ktlint Disallowed

fun main() {
    fun a() {
    }

    fun b()
}

fun main() {
    fun a() {

    }
    fun b()

}

Rule id: standard:no-blank-line-before-rbrace

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-blank-line-before-rbrace")

Enable rule via .editorconfig

ktlint_standard_no-blank-line-before-rbrace = enabled

Disable rule via .editorconfig

ktlint_standard_no-blank-line-before-rbrace = disabled

No blank lines in chained method calls¶

Ktlint Disallowed

fun foo(inputText: String) {
    inputText
        .lowercase(Locale.getDefault())
}

fun foo(inputText: String) {
    inputText

        .lowercase(Locale.getDefault())
}

Rule id: standard:no-blank-lines-in-chained-method-calls

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-blank-lines-in-chained-method-calls")

Enable rule via .editorconfig

ktlint_standard_no-blank-lines-in-chained-method-calls = enabled

Disable rule via .editorconfig

ktlint_standard_no-blank-lines-in-chained-method-calls = disabled

No consecutive blank lines¶

Ktlint Disallowed

package com.test

import com.test.util

val a = "a"

fun b() {
}

fun c()

package com.test


import com.test.util


val a = "a"


fun b() {
}


fun c()

Rule id: standard:no-consecutive-blank-lines

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-consecutive-blank-lines")

Enable rule via .editorconfig

ktlint_standard_no-consecutive-blank-lines = enabled

Disable rule via .editorconfig

ktlint_standard_no-consecutive-blank-lines = disabled

No empty (`{}`) class bodies¶

Ktlint Disallowed

class C

data class DC(val v: Any)

interface I

object O

class C {}

data class DC(val v: Any) { }

interface I {
}

object O{}

Rule id: standard:no-empty-class-body

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-empty-class-body")

Enable rule via .editorconfig

ktlint_standard_no-empty-class-body = enabled

Disable rule via .editorconfig

ktlint_standard_no-empty-class-body = disabled

No leading empty lines in method blocks¶

Ktlint Disallowed

fun bar() {
   val a = 2
}

fun bar() {

   val a = 2
}

Rule id: standard:no-empty-first-line-in-method-block

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-empty-first-line-in-method-block")

Enable rule via .editorconfig

ktlint_standard_no-empty-first-line-in-method-block = enabled

Disable rule via .editorconfig

ktlint_standard_no-empty-first-line-in-method-block = disabled

No line break after else¶

Disallows line breaks after the else keyword if that could lead to confusion, for example:

Ktlint Disallowed

fun funA() {
    if (conditionA()) {
        doSomething()
    } else if (conditionB()) {
        doAnotherThing()
    }
}

fun funA() {
    if (conditionA()) {
        doSomething()
    } else
    if (conditionB()) {
        doAnotherThing()
    }
}

Rule id: standard:no-line-break-after-else

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-line-break-after-else")

Enable rule via .editorconfig

ktlint_standard_no-line-break-after-else = enabled

Disable rule via .editorconfig

ktlint_standard_no-line-break-after-else = disabled

No line break before assignment¶

When a line is broken at an assignment (=) operator the break comes after the symbol.

Ktlint Disallowed

val valA =
    ""

val valA
    = ""

Rule id: standard:no-line-break-before-assignment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-line-break-before-assignment")

Enable rule via .editorconfig

ktlint_standard_no-line-break-before-assignment = enabled

Disable rule via .editorconfig

ktlint_standard_no-line-break-before-assignment = disabled

No multi spaces¶

Except in indentation and in KDoc's it is not allowed to have multiple consecutive spaces.

Ktlint Disallowed

fun main() {
    x(1, 3)
}

fun  main()  {
    x(1,  3)
}

Rule id: standard:no-multi-spaces

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-multi-spaces")

Enable rule via .editorconfig

ktlint_standard_no-multi-spaces = enabled

Disable rule via .editorconfig

ktlint_standard_no-multi-spaces = disabled

No semicolons¶

Avoid using unnecessary semicolons.

Ktlint Disallowed

fun foo() {
    bar()

    bar()
}

fun foo() {
    ;
    bar()
    ;

    bar()

    ;
}

Rule id: standard:no-semi

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-semi")

Enable rule via .editorconfig

ktlint_standard_no-semi = enabled

Disable rule via .editorconfig

ktlint_standard_no-semi = disabled

No trailing whitespaces¶

Rule id: standard:no-trailing-spaces

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-trailing-spaces")

Enable rule via .editorconfig

ktlint_standard_no-trailing-spaces = enabled

Disable rule via .editorconfig

ktlint_standard_no-trailing-spaces = disabled

No `Unit` as return type¶

The Unit type is not allowed as return-type of a function.

Ktlint Disallowed

fun fn() {}

fun fn(): Unit {}

Rule id: standard:no-unit-return

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-unit-return")

Enable rule via .editorconfig

ktlint_standard_no-unit-return = enabled

Disable rule via .editorconfig

ktlint_standard_no-unit-return = disabled

No unused imports¶

Warning

This rule is not able to detect all unused imports as mentioned in this issue comment.

Rule id: standard:no-unused-imports

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-unused-imports")

Enable rule via .editorconfig

ktlint_standard_no-unused-imports = enabled

Disable rule via .editorconfig

ktlint_standard_no-unused-imports = disabled

No wildcard imports¶

No wildcard imports except whitelisted imports.

Ktlint Disallowed

import foobar.Bar
import foobar.Foo

import foobar.*

Configuration setting	ktlint_official	intellij_idea	android_studio
`ij_kotlin_packages_to_use_import_on_demand` Defines allowed wildcard imports as a comma separated list.	-	`java.util.,` `kotlinx.android.synthetic.*`	`java.util.,` `kotlinx.android.synthetic.*`

Warning

In case property ij_kotlin_packages_to_use_import_on_demand is not explicitly set, Intellij IDEA allows wildcards imports like java.util.* which lead to conflicts with the no-wildcard-imports rule. See Intellij IDEA configuration to prevent such conflicts.

Configuration setting ij_kotlin_packages_to_use_import_on_demand is a comma separated string of import paths. This can be a full path, e.g. "java.util.List.", or a wildcard path, e.g. "kotlin.". Use "*" as wildcard for package and all subpackages.

The layout can be composed by the following symbols:

* - wildcard. There must be at least one entry of a single wildcard to match all other imports. Matches anything after a specified symbol/import as well.
| - blank line. Supports only single blank lines between imports. No blank line is allowed in the beginning or end of the layout.
^ - alias import, e.g. "^android.*" will match all android alias imports, "^" will match all other alias imports.

Examples:

ij_kotlin_imports_layout=* # alphabetical with capital letters before lower case letters (e.g. Z before a), no blank lines
ij_kotlin_imports_layout=*,java.**,javax.**,kotlin.**,^ # default IntelliJ IDEA style, same as alphabetical, but with "java", "javax", "kotlin" and alias imports in the end of the imports list
ij_kotlin_imports_layout=android.**,|,^org.junit.**,kotlin.io.Closeable.*,|,*,^ # custom imports layout

Rule id: standard:no-wildcard-imports

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:no-wildcard-imports")

Enable rule via .editorconfig

ktlint_standard_no-wildcard-imports = enabled

Disable rule via .editorconfig

ktlint_standard_no-wildcard-imports = disabled

Spacing¶

Angle bracket spacing¶

No spaces around angle brackets when used for typing.

Ktlint Disallowed

val a: Map<Int, String> = mapOf()
val b: Map<Int, String> = mapOf()
val c: Map<Int, String> = mapOf()

val a: Map< Int, String> = mapOf()
val b: Map<Int, String > = mapOf()
val c: Map <Int, String> = mapOf()

Rule id: standard:spacing-around-angle-brackets

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:spacing-around-angle-brackets")

Enable rule via .editorconfig

ktlint_standard_spacing-around-angle-brackets = enabled

Disable rule via .editorconfig

ktlint_standard_spacing-around-angle-brackets = disabled

Annotation spacing¶

Annotations should be separated by a single line break.

Ktlint Disallowed

@JvmField
fun foo() {}

/**
 * block comment
 */
@Foo @Bar
class FooBar {
}

@JvmField

fun foo() {}

@Foo @Bar
/**
 * block comment
 */
class FooBar {
}

Rule id: standard:annotation-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:annotation-spacing")

Enable rule via .editorconfig

ktlint_standard_annotation-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_annotation-spacing = disabled

Blank line between declarations with annotations¶

Declarations with annotations should be separated by a blank line.

Ktlint Disallowed

fun a()

@Bar
fun b()

fun a()
@Bar
fun b()

Rule id: standard:spacing-between-declarations-with-annotations

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:spacing-between-declarations-with-annotations")

Enable rule via .editorconfig

ktlint_standard_spacing-between-declarations-with-annotations = enabled

Disable rule via .editorconfig

ktlint_standard_spacing-between-declarations-with-annotations = disabled

Blank line between declaration with comments¶

Declarations with comments should be separated by a blank line.

Ktlint Disallowed

// some comment 1
bar()

/*
 * some comment 2
 */
foo()

// some comment 1
bar()
/*
 * some comment 2
 */
foo()

Rule id: standard:spacing-between-declarations-with-comments

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:spacing-between-declarations-with-comments")

Enable rule via .editorconfig

ktlint_standard_spacing-between-declarations-with-comments = enabled

Disable rule via .editorconfig

ktlint_standard_spacing-between-declarations-with-comments = disabled

Colon spacing¶

Consistent spacing around colon.

Ktlint Disallowed

class A : B

class A2 : B2

class A:B

class A2  :  B2

Rule id: standard:colon-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:colon-spacing")

Enable rule via .editorconfig

ktlint_standard_colon-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_colon-spacing = disabled

Comma spacing¶

Consistent spacing around comma.

Ktlint Disallowed

val foo1 = Foo(1, 3)
val foo2 = Foo(1, 3)

val foo1 = Foo(1 ,3)
val foo2 = Foo(1,3)

Rule id: standard:comma-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:comma-spacing")

Enable rule via .editorconfig

ktlint_standard_comma-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_comma-spacing = disabled

Comment spacing¶

The end of line comment sign // should be preceded and followed by exactly a space.

Ktlint Disallowed

// comment
var debugging = false // comment
var debugging = false // comment
var debugging = false // comment

fun main() {
    System.out.println(
        // comment
        "test",
    )
} // comment

//comment
var debugging = false// comment
var debugging = false //comment
var debugging = false//comment

fun main() {
    System.out.println(
         //123
        "test"
    )
}//comment

Rule id: standard:comment-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:comment-spacing")

Enable rule via .editorconfig

ktlint_standard_comment-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_comment-spacing = disabled

Curly spacing¶

Consistent spacing around curly braces.

Ktlint Disallowed

val foo = bar { foo() }

val foo = bar{foo()}

Rule id: standard:curly-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:curly-spacing")

Enable rule via .editorconfig

ktlint_standard_curly-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_curly-spacing = disabled

Dot spacing¶

Consistent spacing around dots.

Ktlint Disallowed

fun String.foo() = "foo"

fun String . foo() = "foo"

Rule id: standard:dot-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:dot-spacing")

Enable rule via .editorconfig

ktlint_standard_dot-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_dot-spacing = disabled

Double colon spacing¶

No spaces around ::.

Ktlint Disallowed

val foo = Foo::class

val foo1 = Foo ::class
val foo2 = Foo:: class
val foo3 = Foo :: class
val foo4 = Foo::
    class

Rule id: standard:double-colon-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:double-colon-spacing")

Enable rule via .editorconfig

ktlint_standard_double-colon-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_double-colon-spacing = disabled

Function return type spacing¶

Consistent spacing around the function return type.

Ktlint Disallowed

fun foo(): String = "some-result"

fun foo1() : String = "some-result"

fun foo2():  String = "some-result"

fun foo3():String = "some-result"

fun foo4():
    String = "some-result"

Rule id: standard:function-return-type-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-return-type-spacing")

Enable rule via .editorconfig

ktlint_standard_function-return-type-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_function-return-type-spacing = disabled

Function start of body spacing¶

Consistent spacing before start of function body.

Ktlint Disallowed

// In case `ktlint_function_signature_body_expression_wrapping` is set to `default` or `multiline`
fun foo1() = "some-result"

// In case `ktlint_function_signature_body_expression_wrapping` is set to `always`
fun foo2() =
    "some-result"

fun foo3() {
    // do something
}

// In case `ktlint_function_signature_body_expression_wrapping` is set to `default` or `multiline`
fun bar1(): String = "some-result"

// In case `ktlint_function_signature_body_expression_wrapping` is set to `always`
fun bar2(): String =
    "some-result"

fun bar3(): String {
    doSomething()
    return "some-result"
}

fun foo1()= "some-result"

fun foo2()
    = "some-result"

fun foo3()
{
    // do something
}

fun bar1(): String= "some-result"

fun bar2(): String
    = "some-result"

fun bar3(): String
{
    return "some-result"
}

Rule id: standard:function-start-of-body-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-start-of-body-spacing")

Enable rule via .editorconfig

ktlint_standard_function-start-of-body-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_function-start-of-body-spacing = disabled

Function type reference spacing¶

Consistent spacing in the type reference before a function.

Ktlint Disallowed

fun String.foo() = "some-result"

fun String .foo() = "some-result"
fun String
    .foo() = "some-result"
fun String? .foo() = "some-result"
fun String?
    .foo() = "some-result"

Rule id: standard:function-type-reference-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:function-type-reference-spacing")

Enable rule via .editorconfig

ktlint_standard_function-type-reference-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_function-type-reference-spacing = disabled

Fun keyword spacing¶

Consistent spacing after the fun keyword.

Ktlint Disallowed

fun foo() = "some-result"

fun  foo() = "some-result"
fun
foo() = "some-result"

Rule id: standard:fun-keyword-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:fun-keyword-spacing")

Enable rule via .editorconfig

ktlint_standard_fun-keyword-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_fun-keyword-spacing = disabled

Kdoc wrapping¶

A KDoc comment should start and end on a line that does not contain any other element.

Ktlint Disallowed

/** Some KDoc comment 1 */
val foo1 = "foo1"

/** Some KDoc comment 1 */ val foo1 = "foo1"
val foo2 = "foo2" /** Some KDoc comment
                   * with a newline
                   */

Rule id: standard:kdoc-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:kdoc-wrapping")

Enable rule via .editorconfig

ktlint_standard_kdoc-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_kdoc-wrapping = disabled

Keyword spacing¶

Consistent spacing around keywords.

Ktlint Disallowed

fun main() {
    if (true) {
        doSomething()
    }
}

fun main() {
    if(true) {
        doSomething()
    }
}

Rule id: standard:keyword-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:keyword-spacing")

Enable rule via .editorconfig

ktlint_standard_keyword-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_keyword-spacing = disabled

Modifier list spacing¶

Consistent spacing between modifiers in and after the last modifier in a modifier list.

Ktlint Disallowed

abstract class Foo {
    protected abstract suspend fun execute()
}

abstract  class Foo {
    protected  abstract  suspend  fun execute()
}
abstract
class Foo {
    protected
    abstract
    suspend
    fun execute()
}

Rule id: standard:modifier-list-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:modifier-list-spacing")

Enable rule via .editorconfig

ktlint_standard_modifier-list-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_modifier-list-spacing = disabled

Nullable type spacing¶

No spaces in a nullable type.

Ktlint Disallowed

val foo: String? = null
val foo: List<String?> = listOf(null)

val foo: String ? = null
val foo: List<String ?> = listOf(null)

Rule id: standard:nullable-type-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:nullable-type-spacing")

Enable rule via .editorconfig

ktlint_standard_nullable-type-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_nullable-type-spacing = disabled

Operator spacing¶

Consistent spacing around operators.

Ktlint Disallowed

val foo1 = 1 + 2
val foo2 = 1 - 2
val foo3 = 1 * 2
val foo4 = 1 / 2

val foo1 = 1+2
val foo2 = 1- 2
val foo3 = 1 *2
val foo4 = 1  /  2

Rule id: standard:op-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:op-spacing")

Enable rule via .editorconfig

ktlint_standard_op-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_op-spacing = disabled

Parameter list spacing¶

Consistent spacing inside the parameter list.

Ktlint Disallowed

fun foo(a: Any) = "some-result"

fun foo() = "some-result"

fun foo( a : Any ) = "some-result"
fun foo(
) = "some-result"

Rule id: standard:parameter-list-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:parameter-list-spacing")

Enable rule via .editorconfig

ktlint_standard_parameter-list-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_parameter-list-spacing = disabled

Parenthesis spacing¶

Consistent spacing around parenthesis.

Ktlint Disallowed

class Foo : Bar {
    constructor(string: String) : super()
}

val foo1 = ((1 + 2) / 3)

class Foo : Bar {
    constructor(string: String) : super ()
}

val foo1 = ( (1 + 2 ) / 3)

Rule id: standard:paren-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:paren-spacing")

Enable rule via .editorconfig

ktlint_standard_paren-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_paren-spacing = disabled

Range spacing¶

Consistent spacing around range operators.

Ktlint Disallowed

val foo1 = (1..12 step 2).last
val foo2 = (1..12 step 2).last
val foo3 = (1..12 step 2).last

val foo1 = (1.. 12 step 2).last
val foo2 = (1 .. 12 step 2).last
val foo3 = (1 ..12 step 2).last

Rule id: standard:range-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:range-spacing")

Enable rule via .editorconfig

ktlint_standard_range-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_range-spacing = disabled

Spacing between function name and opening parenthesis¶

Consistent spacing between function name and opening parenthesis.

Ktlint Disallowed

fun foo() = "foo"

fun foo () = "foo"

Rule id: standard:spacing-between-function-name-and-opening-parenthesis

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:spacing-between-function-name-and-opening-parenthesis")

Enable rule via .editorconfig

ktlint_standard_spacing-between-function-name-and-opening-parenthesis = enabled

Disable rule via .editorconfig

ktlint_standard_spacing-between-function-name-and-opening-parenthesis = disabled

Try catch finally spacing¶

Enforce consistent spacing in try { .. } catch { .. } finally { .. }.

Ktlint Disallowed

fun foo() =
    try {
        // do something
    } catch (exception: Exception) {
        // handle exception
    } finally {
        // clean up
    }

fun foo1() = try { /* ... */ } catch (exception: Exception) { /* ... */ } finally { /* ... */ }
fun foo2() = 
    try {
        // do something
    }
    catch (exception: Exception) {
        // handle exception
    }
    finally {
        // clean up
    }

Rule id: standard:try-catch-finally-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:try-catch-finally-spacing")

Enable rule via .editorconfig

ktlint_standard_try-catch-finally-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_try-catch-finally-spacing = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Type argument list spacing¶

Spacing before and after the angle brackets of a type argument list.

Ktlint Disallowed

val res = ArrayList<LintError>()

class B<T> : A<T>() {
    override fun x() = super<A>.x()
}

val res = ArrayList < LintError > ()

class B<T> : A< T >() {
    override fun x() = super< A >.x()
}

Rule id: standard:type-argument-list-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:type-argument-list-spacing")

Enable rule via .editorconfig

ktlint_standard_type-argument-list-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_type-argument-list-spacing = disabled

Type parameter list spacing¶

Spacing after a type parameter list in function and class declarations.

Ktlint Disallowed

fun <T> foo1(t: T) = "some-result"

fun <T> foo2(t: T) = "some-result"

fun <T> foo3(t: T) = "some-result"

fun<T> foo1(t: T) = "some-result"

fun <T>foo2(t: T) = "some-result"

fun<T>foo3(t: T) = "some-result"

Rule id: standard:type-parameter-list-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:type-parameter-list-spacing")

Enable rule via .editorconfig

ktlint_standard_type-parameter-list-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_type-parameter-list-spacing = disabled

Unary operator spacing¶

No spaces around unary operators.

Ktlint Disallowed

fun foo1(i: Int) = i++

fun foo2(i: Int) = ++i

fun foo3(i: Int) = ++i

fun foo1(i: Int) = i ++

fun foo2(i: Int) = ++ i

fun foo3(i: Int) = ++
    i

Rule id: standard:unary-op-spacing

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:unary-op-spacing")

Enable rule via .editorconfig

ktlint_standard_unary-op-spacing = enabled

Disable rule via .editorconfig

ktlint_standard_unary-op-spacing = disabled

String template¶

Consistent string templates ($v instead of ${v}, ${p.v} instead of ${p.v.toString()})

Ktlint Disallowed

val foo = "$foo hello"

val foo = "${foo} hello"

Rule id: standard:string-template

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:string-template")

Enable rule via .editorconfig

ktlint_standard_string-template = enabled

Disable rule via .editorconfig

ktlint_standard_string-template = disabled

String template indent¶

Enforce consistent string template indentation for multiline string templates which are post-fixed with .trimIndent(). The opening and closing """ are placed on separate lines and the indentation of the content of the template is aligned with the """.

Ktlint Disallowed

val foo =
    """
    line1
    line2
    """.trimIndent()

fun foo() {
    // The opening """ can not be wrapped to next line as that would result in a compilation error
    return """
        line1
        line2
        """.trimIndent()
}

val foo = """
          line1
          line2
          """.trimIndent()

fun foo() {
    return """
        line1
        line2
    """.trimIndent()
}

Rule id: standard:string-template-indent

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:string-template-indent")

Enable rule via .editorconfig

ktlint_standard_string-template-indent = enabled

Disable rule via .editorconfig

ktlint_standard_string-template-indent = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Trailing comma on call site¶

Consistent removal (default) or adding of trailing commas on call site.

Ktlint Disallowed

val foo =
    FooWrapper(
        Foo(
            a = 3,
            b = 4,
        ),
    )

val foo =
    FooWrapper(Foo(
        a = 3,
        b = 4,
    ),) // it's weird to insert "," between unwrapped (continued) parenthesis

Configuration setting	ktlint_official	intellij_idea	android_studio
`ij_kotlin_allow_trailing_comma_on_call_site` Defines whether a trailing comma (or no trailing comma) should be enforced on the calling site, e.g. argument-list, when-entries, lambda-arguments, indices, etc. When set, IntelliJ IDEA uses this property to allow usage of a trailing comma by discretion of the developer. KtLint however uses this setting to enforce consistent usage of the trailing comma when set.	`true`	`true`	`false`

Note

Although the Kotlin coding conventions leaves it to the developer's discretion to use trailing commas on the call site, it also states that usage of trailing commas has several benefits:

It makes version-control diffs cleaner – as all the focus is on the changed value.
It makes it easy to add and reorder elements – there is no need to add or delete the comma if you manipulate elements.
It simplifies code generation, for example, for object initializers. The last element can also have a comma.

KtLint values consistent formatting more than a per-situation decision, and therefore uses this setting to enforce/disallow usage of trailing comma's on the calling site.

Rule id: standard:trailing-comma-on-call-site

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:trailing-comma-on-call-site")

Enable rule via .editorconfig

ktlint_standard_trailing-comma-on-call-site = enabled

Disable rule via .editorconfig

ktlint_standard_trailing-comma-on-call-site = disabled

Trailing comma on declaration site¶

Consistent removal (default) or adding of trailing commas on declaration site.

Ktlint Disallowed

class FooWrapper(
    val foo = Foo(
        a = 3,
        b = 4,
    ),
)

class FooWrapper(val foo = Foo(
    a = 3,
    b = 4,
),) // it's weird to insert "," between unwrapped (continued) parenthesis

Configuration setting	ktlint_official	intellij_idea	android_studio
`ij_kotlin_allow_trailing_comma` Defines whether a trailing comma (or no trailing comma) should be enforced on the defining site, e.g. parameter-list, type-argument-list, lambda-value-parameters, enum-entries, etc. When set, IntelliJ IDEA uses this property to allow usage of a trailing comma by discretion of the developer. KtLint however uses this setting to enforce consistent usage of the trailing comma when set.	`true`	`true`	`false`

Note

The Kotlin coding conventions encourages the usage of trailing commas on the declaration site, but leaves it to the developer's discretion to use trailing commas on the call site. But next to this, it also states that usage of trailing commas has several benefits:

It makes version-control diffs cleaner – as all the focus is on the changed value.
It makes it easy to add and reorder elements – there is no need to add or delete the comma if you manipulate elements.
It simplifies code generation, for example, for object initializers. The last element can also have a comma.

KtLint values consistent formatting more than a per-situation decision, and therefore uses this setting to enforce/disallow usage of trailing comma's in declarations.

Rule id: standard:trailing-comma-on-declaration-site

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:trailing-comma-on-declaration-site")

Enable rule via .editorconfig

ktlint_standard_trailing-comma-on-declaration-site = enabled

Disable rule via .editorconfig

ktlint_standard_trailing-comma-on-declaration-site = disabled

Type argument comment¶

Disallows comments to be placed at certain locations inside a type argument.

Ktlint Disallowed

fun Foo<
    /* some comment */ 
    out Any
    >.foo() {}
fun Foo<
    // some comment 
    out Any
    >.foo() {}

fun Foo<out /* some comment */ Any>.foo() {}
fun Foo<
    out Any, // some comment
    >.foo() {}

Note

In some projects it is an accepted practice to use EOL comments to document the parameter before the comma as is shown below:

fun Foo<
    out Bar1, // some comment
    out Bar2, // some other comment
>.foo() {}

Although this code sample might look ok, it is semantically and programmatically unclear to which type some comment refers. From the developer perspective it might be clear that it belongs to type Bar1. From the parsers perspective, it does belong to type Bar2.

Rule id: standard:type-argument-comment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:type-argument-comment")

Enable rule via .editorconfig

ktlint_standard_type-argument-comment = enabled

Disable rule via .editorconfig

ktlint_standard_type-argument-comment = disabled

Type parameter comment¶

Disallows comments to be placed at certain locations inside a type parameter.

Ktlint Disallowed

class Foo1<
    /* some comment */ 
    out Bar
    >
class Foo2<
    // some comment 
    out Bar
    >

class Foo1<in /* some comment */ Bar>
class Foo2<
    in Bar, // some comment
    >

Note

In some projects it is an accepted practice to use EOL comments to document the parameter before the comma as is shown below:

class Foo<
    out Bar1, // some comment
    out Bar2, // some other comment
>

Although this code sample might look ok, it is semantically and programmatically unclear on which parameter some comment refers. From the developer perspective it might be clear that it belongs to type Bar1. From the parsers perspective, it does belong to type Bar2.

Rule id: standard:type-parameter-comment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:type-parameter-comment")

Enable rule via .editorconfig

ktlint_standard_type-parameter-comment = enabled

Disable rule via .editorconfig

ktlint_standard_type-parameter-comment = disabled

Unnecessary parenthesis before trailing lambda¶

An empty parentheses block before a lambda is redundant.

Ktlint Disallowed

val foo = "some-string".count { it == '-' }

val foo = "some-string".count() { it == '-' }

Rule id: standard:unnecessary-parentheses-before-trailing-lambda

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:unnecessary-parentheses-before-trailing-lambda")

Enable rule via .editorconfig

ktlint_standard_unnecessary-parentheses-before-trailing-lambda = enabled

Disable rule via .editorconfig

ktlint_standard_unnecessary-parentheses-before-trailing-lambda = disabled

Value argument comment¶

Disallows comments to be placed at certain locations inside a value argument.

Ktlint Disallowed

val foo1 =
    foo(
        /* some comment */
        bar = "bar"
    )
val foo2 =
    foo(
        // some comment
        bar = "bar"
    )

val foo1 = foo(bar /* some comment */ = "bar")
val foo2 = 
    foo(
        bar = // some comment
            "bar"
    )

Rule id: standard:value-argument-comment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:value-argument-comment")

Enable rule via .editorconfig

ktlint_standard_value-argument-comment = enabled

Disable rule via .editorconfig

ktlint_standard_value-argument-comment = disabled

Value parameter comment¶

Disallows comments to be placed at certain locations inside a value argument.

Ktlint Disallowed

class Foo1(
    /** some kdoc */
    bar = "bar"
)
class Foo2(
    /* some comment */
    bar = "bar"
)
class Foo3(
    // some comment
    bar = "bar"
)

class Foo1(
   bar = /** some kdoc */ "bar"
)
class Foo2(
   bar = /* some comment */ "bar"
)
class Foo3(
    bar =
       // some comment
       "bar"
)

Rule id: standard:value-parameter-comment

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:value-parameter-comment")

Enable rule via .editorconfig

ktlint_standard_value-parameter-comment = enabled

Disable rule via .editorconfig

ktlint_standard_value-parameter-comment = disabled

Wrapping¶

Argument list wrapping¶

All arguments should be on the same line, or every argument should be on a separate line.

Ktlint Disallowed

val foo =
    foo(
        a,
        b,
        c,
    )

val foo =
    foo(
        a,
        b, c,
    )

Configuration setting	ktlint_official	intellij_idea	android_studio
`ktlint_argument_list_wrapping_ignore_when_parameter_count_greater_or_equal_than`	`unset`	8	8

Rule id: standard:argument-list-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:argument-list-wrapping")

Enable rule via .editorconfig

ktlint_standard_argument-list-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_argument-list-wrapping = disabled

Chain wrapping¶

When wrapping chained calls ., ?. and ?: should be placed on the next line

Ktlint Disallowed

val foo =
    listOf(1, 2, 3)
        .filter { it > 2 }!!
        .takeIf { it.count() > 100 }
        ?.sum()
val foobar =
    foo()
        ?: bar

val foo =
    listOf(1, 2, 3).
        filter { it > 2 }!!.
        takeIf { it.count() > 100 }?.
        sum()
val foobar =
    foo() ?:
        bar

Rule id: standard:chain-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:chain-wrapping")

Enable rule via .editorconfig

ktlint_standard_chain-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_chain-wrapping = disabled

Comment wrapping¶

A block comment should start and end on a line that does not contain any other element.

Ktlint Disallowed

// Some comment 1
val foo1 = "foo1"
val foo2 = "foo" // Some comment
val foo3 = { /* no-op */ }

/* Some comment 1 */ val foo1 = "foo1"
val foo2 = "foo" /* Block comment instead of end-of-line comment */
val foo3 = "foo" /* Some comment
                  * with a newline
                  */

Rule id: standard:comment-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:comment-wrapping")

Enable rule via .editorconfig

ktlint_standard_comment-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_comment-wrapping = disabled

Condition wrapping¶

Wraps each operand in a multiline condition to a separate line.

Ktlint Disallowed

val foo = bar || baz
if (bar1 ||
    bar2 ||
    baz1 ||
    (baz2 && baz3)
) {
   // do something
}

val foo =
  multiLineOperand(
      "bar"
  ) || baz
if (bar1 || bar2 ||
    baz1 || (baz2 && baz3)
) {
   // do something
}

Rule id: standard:condition-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:condition-wrapping")

Enable rule via .editorconfig

ktlint_standard_condition-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_condition-wrapping = disabled

Content receiver wrapping¶

Wraps the content receiver list to a separate line regardless of maximum line length. If the maximum line length is configured and is exceeded, wrap the context receivers and if needed its projection types to separate lines.

Ktlint Disallowed

// Always wrap regardless of whether max line length is set
context(Foo)
fun fooBar()

// Wrap each context receiver to a separate line when the
// entire context receiver list does not fit on a single line
context(
    Fooooooooooooooooooo1,
    Foooooooooooooooooooooooooooooo2
)
fun fooBar()

// Wrap each context receiver to a separate line when the
// entire context receiver list does not fit on a single line.
// Also, wrap each of it projection types in case a context
// receiver does not fit on a single line after it has been
// wrapped.
context(
    Foooooooooooooooo<
        Foo,
        Bar,
        >
)
fun fooBar()

// Should be wrapped regardless of whether max line length is set
context(Foo) fun fooBar()

// Should be wrapped when the entire context receiver list does not
// fit on a single line
context(Fooooooooooooooooooo1, Foooooooooooooooooooooooooooooo2)
fun fooBar()

// Should be wrapped when the entire context receiver list does not
// fit on a single line. Also, it should wrap each of it projection
// type in case a context receiver does not fit on a single line 
// after it has been wrapped.
context(Foooooooooooooooo<Foo, Bar>)
fun fooBar()

Rule id: standard:context-receiver-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:context-receiver-wrapping")

Enable rule via .editorconfig

ktlint_standard_context-receiver-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_context-receiver-wrapping = disabled

Enum wrapping¶

An enum should be a single line, or each enum entry has to be placed on a separate line. In case the enumeration contains enum entries and declarations those are to be separated by a blank line.

Ktlint Disallowed

enum class Foo { A, B, C, D }

enum class Foo {
    A,
    B,
    C,
    D,
    ;

    fun foo() = "foo"
}

enum class Foo {
    A,
    B, C,
    D
}

enum class Foo {
    A;
    fun foo() = "foo"
}

Rule id: standard:enum-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:enum-wrapping")

Enable rule via .editorconfig

ktlint_standard_enum-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_enum-wrapping = disabled

If else wrapping¶

A single line if-statement should be kept simple. It may contain no more than one else-branch. The branches may not be wrapped in a block.

Ktlint Disallowed

fun foobar() {
    if (true) foo()
    if (true) foo() else bar()
}

fun foobar() {
    if (true) if (false) foo() else bar()
    if (true) bar() else if (false) foo() else bar()
    if (true) { foo() } else bar()
    if (true) bar() else { if (false) foo() else bar() }
}

Rule id: standard:if-else-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:if-else-wrapping")

Enable rule via .editorconfig

ktlint_standard_if-else-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_if-else-wrapping = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Multiline expression wrapping¶

Multiline expression on the right hand side of an expression are forced to start on a separate line. Expressions in return statement are excluded as that would result in a compilation error.

Ktlint Disallowed

val foo =
    foo(
        parameterName =
            "The quick brown fox "
                .plus("jumps ")
                .plus("over the lazy dog"),
    )

val foo = foo(
    parameterName = "The quick brown fox "
        .plus("jumps ")
        .plus("over the lazy dog"),
)

Rule id: standard:multiline-expression-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:multiline-expression-wrapping")

Enable rule via .editorconfig

ktlint_standard_multiline-expression-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_multiline-expression-wrapping = disabled

Note

This rule is only run when ktlint_code_style is set to ktlint_official or when the rule is enabled explicitly.

Parameter list wrapping¶

When class/function signature doesn't fit on a single line, each parameter must be on a separate line.

Note

Wrapping of parameters is also influenced by the function-signature rule.

Ktlint Disallowed (ktlint_official) Disallowed (non ktlint_official)"

// If `ktlint_class_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than` equals
// `unset` the parameters are not wrapped as long as they fit on a single line
class ClassA(paramA: String, paramB: String, paramC: String)

class ClassA(
    paramA: String,
    paramB: String,
    paramC: String
)

// If `ktlint_function_signature_rule_force_multiline_when_parameter_count_greater_or_equal_than` equals
// `unset` the parameters are not wrapped as long as they fit on a single line
fun f(a: Any, b: Any, c: Any)

fun f(
    a: Any,
    b: Any,
    c: Any
)

fun foo(
    @Bar fooBar: FooBar
)

class ClassA(
    paramA: String, paramB: String,
    paramC: String
)

fun f(
    a: Any,
    b: Any, c: Any
)

fun foo(@Bar fooBar: FooBar)

class ClassA(
    paramA: String, paramB: String,
    paramC: String
)

fun f(
    a: Any,
    b: Any, c: Any
)

Rule id: standard:parameter-list-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:parameter-list-wrapping")

Enable rule via .editorconfig

ktlint_standard_parameter-list-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_parameter-list-wrapping = disabled

Parameter wrapping¶

When a function or class parameter doesn't fit on a single line, wrap the type or value to a separate line

Ktlint (ktlint_official) Ktlint (non ktlint_official) Disallowed

// Assume that the last allowed character is
// at the X character on the right           X
class Bar(
    val fooooooooooooooooooooooooTooLong:
        Foo,
)

fun bar(
    fooooooooooooooooooooooooTooLong:
        Foo,
)

// Assume that the last allowed character is
// at the X character on the right           X
class Bar(
    val fooooooooooooooooooooooooTooLong:
    Foo,
)

fun bar(
    fooooooooooooooooooooooooTooLong:
    Foo,
)

// Assume that the last allowed character is
// at the X character on the right           X
class Bar(
    val fooooooooooooooooooooooooTooLong: Foo,
)

fun bar(
    fooooooooooooooooooooooooooooTooLong: Foo,
)

Rule id: standard:parameter-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:parameter-wrapping")

Enable rule via .editorconfig

ktlint_standard_parameter-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_parameter-wrapping = disabled

Property wrapping¶

When a property doesn't fit on a single line, wrap the type or value to a separate line

Ktlint Disallowed

// Assume that the last allowed character is
// at the X character on the right           X
val aVariableWithALooooooooooooongName:
    String

// Assume that the last allowed character is
// at the X character on the right           X
val aVariableWithALooooooooooooongName: String

Rule id: standard:property-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:property-wrapping")

Enable rule via .editorconfig

ktlint_standard_property-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_property-wrapping = disabled

Statement wrapping¶

A function, class/object body or other block body statement has to be placed on different line than the braces of the body block.

Ktlint Disallowed

fun foo() {
    if (true) {
        // do something
    }
}

class A {
    val a = 0
    val b = 1
}

enum class FooBar1 { FOO, BAR }

enum class FooBar2 {
    FOO,
    BAR,
}

fun foo() { if (true) {
        // do something
    }
}

class A { val a = 0
    val b = 1 }

Rule id: standard:statement-wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:statement-wrapping")

Enable rule via .editorconfig

ktlint_standard_statement-wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_statement-wrapping = disabled

Wrapping¶

Inserts missing newlines (for example between parentheses of a multi-line function call).

Ktlint Disallowed

val foo =
    foo(
        a,
        b,
        c,
    )

val foo = foo(
    a,
    b,
    c)

Rule id: standard:wrapping

Suppress or disable rule (1)

Suppress rule in code with annotation below:

@Suppress("ktlint:standard:wrapping")

Enable rule via .editorconfig

ktlint_standard_wrapping = enabled

Disable rule via .editorconfig

ktlint_standard_wrapping = disabled

Standard rules

Annotation formatting¶

Binary expression wrapping¶

Blank line before declarations¶

Block comment initial star alignment¶

Chain method continuation¶

Class signature¶

Enum entry¶

File name¶

Final newline¶

Function expression body¶

Function literal¶

Function signature¶

Function type modifier spacing¶

If else bracing¶

Import ordering¶

Indentation¶

Naming¶

Backing property naming¶

Class naming¶

Function naming¶

Package name¶

Property naming¶

No blank lines in list¶

No consecutive comments¶

No empty file¶

No empty first line at start in class body¶

No single line block comment¶

Ktlint-suppression rule¶

Max line length¶

Modifier order¶

Multiline if-else¶

Multiline loop¶

No blank lines before }¶

No blank lines in chained method calls¶

No consecutive blank lines¶

No empty ({}) class bodies¶

No leading empty lines in method blocks¶

No line break after else¶

No line break before assignment¶

No multi spaces¶

No semicolons¶

No trailing whitespaces¶

No Unit as return type¶

No unused imports¶

No wildcard imports¶

Spacing¶

Angle bracket spacing¶

Annotation spacing¶

Blank line between declarations with annotations¶

Blank line between declaration with comments¶

Colon spacing¶

Comma spacing¶

Comment spacing¶

Curly spacing¶

Dot spacing¶

Double colon spacing¶

Function return type spacing¶

Function start of body spacing¶

Function type reference spacing¶

Fun keyword spacing¶

Kdoc wrapping¶

Keyword spacing¶

Modifier list spacing¶

Nullable type spacing¶

Operator spacing¶

Parameter list spacing¶

Parenthesis spacing¶

Range spacing¶

Spacing between function name and opening parenthesis¶

Try catch finally spacing¶

Type argument list spacing¶

Type parameter list spacing¶

Unary operator spacing¶

String template¶

String template indent¶

Trailing comma on call site¶

Trailing comma on declaration site¶

Type argument comment¶

Type parameter comment¶

No blank lines before `}`¶

No empty (`{}`) class bodies¶

No `Unit` as return type¶