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
Rule-id: annotation
Argument list wrapping¶
Rule-id: argument-list-wrapping
Chain wrapping¶
When wrapping chained calls ., ?. and ?: should be placed on the next line
Rule id: chain-wrapping
Enum entry¶
Enum entry names should be uppercase underscore-separated names.
Rule id: enum-entry-name-case
File name¶
Files containing only one toplevel domain should be named according to that element.
Rule id: filename
Final newline¶
Ensures consistent usage of a newline at the end of each file.
This rule can be configured with .editorconfig property insert_final_newline.
Rule id: final-newline
Import ordering¶
Imports ordered consistently (see Custom ktlint EditorConfig properties for more)
Rule id: import-ordering
Indentation¶
Indentation formatting - respects .editorconfig indent_size with no continuation indent (see EditorConfig section for more).
Rule id: indent
Max line length¶
Ensures that lines do not exceed the given length of .editorconfig property max_line_length (see EditorConfig section for more). This rule does not apply in a number of situations. For example, in the case a line exceeds the maximum line length due to and comment that disables ktlint rules than that comment is being ignored when validating the length of the line. 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.
Rule id: max-line-length
Modifier order¶
Consistent order of modifiers
Rule id: modifier-order
Multiline if-else¶
Braces required for multiline if/else statements.
Rule id: multiline-if-else
No blank lines before }¶
No blank lines before }.
Rule id: no-blank-line-before-rbrace
No blank lines in chained method calls¶
Rule id: no-blank-lines-in-chained-method-calls
No consecutive blank lines¶
Rule id: no-consecutive-blank-lines
No empty ({}) class bodies¶
Rule id: no-empty-class-body
No leading empty lines in method blocks¶
Rule id: no-empty-first-line-in-method-block
No line break after else¶
Disallows line breaks after the else keyword if that could lead to confusion, for example:
Rule id: no-line-break-after-else
No line break before assignment¶
When a line is broken at an assignment (=) operator the break comes after the symbol.
Rule id: no-line-break-before-assignment
No multi spaces¶
Except in indentation and in KDoc's it is not allowed to have multiple consecutive spaces.
Rule id: no-multi-spaces
No semicolons¶
No semicolons (unless used to separate multiple statements on the same line).
Rule id: no-semi
No trailing whitespaces¶
Rule id: no-trailing-spaces
No Unit as return type¶
The Unit type is not allowed as return type of a function.
returns (fun fn {} instead of fun fn: Unit {})
Rule id: no-unit-return
No unused imports¶
Rule id: no-unused-imports
No wildcard imports¶
No wildcard imports except imports listed in .editorconfig property ij_kotlin_packages_to_use_import_on_demand.
Rule id: no-wildcard-imports
Package name¶
Validates that the package name matches the regular expression [a-z][a-zA-Z\d]*(\.[a-z][a-zA-Z\d]*)*.
Rule id: package-name
Parameter list wrapping¶
When class/function signature doesn't fit on a single line, each parameter must be on a separate line
Rule id: parameter-list-wrapping
String template¶
Consistent string templates ($v instead of ${v}, ${p.v} instead of ${p.v.toString()})
Rule id: string-template
Trailing comma on call site¶
Consistent removal (default) or adding of trailing comma's on call site.
Important
KtLint uses the IntelliJ IDEA .editorconfig property ij_kotlin_allow_trailing_comma_on_call_site to configure the rule. When this property is enabled, KtLint enforces the usage of the trailing comma at call site while IntelliJ IDEA default formatter only allows to use the trailing comma but leaves it to the developer's discretion to actually use it (or not). KtLint values consistent formatting more than a per-situation decision.
Note
In KtLint 0.48.x the default value for using the trailing comma on call site has been changed to true except when codestyle android is used.
Although the Kotlin coding conventions](https://kotlinlang.org/docs/reference/coding-conventions.html#names-for-test-methods) leaves it to the developer's discretion to use trailing comma's 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.
Rule id: trailing-comma-on-call-site
Trailing comma on declaration site¶
Consistent removal (default) or adding of trailing comma's on declaration site.
Important
KtLint uses the IntelliJ IDEA .editorconfig property ij_kotlin_allow_trailing_comma to configure the rule. When this property is enabled, KtLint enforces the usage of the trailing comma at declaration site while IntelliJ IDEA default formatter only allows to use the trailing comma but leaves it to the developer's discretion to actually use it (or not). KtLint values consistent formatting more than a per-situation decision.
Note
In KtLint 0.48.x the default value for using the trailing comma on declaration site has been changed to true except when codestyle android is used.
The Kotlin coding conventions](https://kotlinlang.org/docs/reference/coding-conventions.html#names-for-test-methods) encourages the usage of trailing comma's on the declaration site, but leaves it to the developer's discretion to use trailing comma's 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.
Rule id: trailing-comma-on-declaration-site
Wrapping¶
Inserts missing newlines (for example between parentheses of a multi-line function call).
Rule id: wrapping
Spacing¶
Annotation spacing¶
Annotations should be separated by a single line break.
Rule id: annotation-spacing
Colon spacing¶
Consistent spacing around colon.
Rule id: colon-spacing
Comma spacing¶
Consistent spacing around comma.
Rule id: comma-spacing
Comment spacing¶
The end of line comment sign // should be preceded and followed by exactly a space.
Rule id: comment-spacing
Curly spacing¶
Consistent spacing around curly braces.
Rule id: curly-spacing
Dot spacing¶
Consistent spacing around dots.
Rule id: dot-spacing
Double colon spacing¶
No spaces around ::.
Rule id: double-colon-spacing
Keyword spacing¶
Consistent spacing around keywords.
Rule id: keyword-spacing
Operator spacing¶
Consistent spacing around operators.
Rule id: op-spacing
Parenthesis spacing¶
Consistent spacing around parenthesis.
Rule id: paren-spacing
Range spacing¶
Consistent spacing around range operators.
Rule id: range-spacing
Angle bracket spacing¶
No spaces around angle brackets when used for typing.
Rule id: spacing-around-angle-brackets
Blank line between declarations with annotations¶
Declarations with annotations should be separated by a blank line.
Rule id: spacing-between-declarations-with-annotations
Blank line between declaration with comments¶
Declarations with comments should be separated by a blank line.
Rule id: spacing-between-declarations-with-comments
Unary operator spacing¶
No spaces around unary operators.
Rule id: unary-op-spacing