⌘ K
kotlin · brace indent · live · client-side

Format Kotlin source files

A brace-tracking indenter for Kotlin. Re-indents classes, lambdas, and data classes. Use ktlint for production. Runs locally.

Kotlin Formatter
Input
47 B
1 lines
Output
48 B
2 lines
Status
ready
live
Ratio
1.02×
out/in
input · kotlin
output · formatted kotlin
fun greet(name:String){println("Hello, $name")}
Quick Start

How to format Kotlin

Counts brace depth across data classes, sealed hierarchies, and lambda bodies — re-pads each line to match.

  1. 01

    Paste Kotlin source

    Classes, data classes, lambdas, and trailing-lambda DSLs all work.

    Parsing runs through Prettier’s standalone bundle (or the language-specific equivalent) loaded lazily — no parser ships until the tool is opened.

    kotlinPrettierASTstandalonelazy
    input · sourceraw · AST
    fun f(){}
    loaded · parsedAST · ready
  2. 02

    Pick indent width

    4 spaces is the official Kotlin style; 2 is occasionally used.

    Indent width, tab style, and print-width re-format through a memoised pass — switching 2 → 4 spaces never re-parses, only re-prints.

    optionsindentprint-widthmemoisedlive
    opts · optionsindent · live
    indent=4
    options applied · livelive
  3. 03

    Watch blocks align

    Class bodies, function blocks, and lambdas indent one level deeper per brace.

    The formatter is deterministic and idempotent: running it twice produces byte-identical output, which keeps diffs and git noise to a minimum.

    liveidempotentdeterministicdiff-cleanstable
    out · formattedindented · ready
    fun f() {
    println("hi")
}
    formatted · liveidempotent
  4. 04

    Copy or download

    Export as .kt or copy. Source stays in your browser.

    Download writes a Blob with the language-appropriate extension; copy uses navigator.clipboard.writeText so the output preserves all whitespace exactly.

    exportclipboardbloblanguage MIMEclient-side
    ok · copiedready · done
    ✓ Copied
    shipped · ready to shipsuccess
Pro tips

Formatting tips that keep diffs sane

Pick one config and pin it

Inconsistent formatting causes diff churn. Commit .prettierrc / .editorconfig and enforce in CI.

Format on save

Editor integration is faster feedback than a pre-commit hook. Use both for belt-and-braces.

Idempotency matters

Running the formatter twice should produce identical output. Test this on a representative file.

Match the language community

Default to community conventions: 2 spaces for JS/CSS, 4 for Python, tabs for Go. Fights over indent are a productivity tax.

Print-width drives wrapping

80, 100, and 120 are the common targets. Wider lines parse fast but review slower side-by-side.

Don’t mix formatters and linters

Prettier handles whitespace; ESLint handles correctness. Disable overlapping rules to avoid fight-club configs.

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Use Cases

When to format Kotlin

Android samples, build scripts, gist cleanup.

Android samples

Re-indent compressed Compose or View-based snippets. Idempotent: running the formatter twice produces byte-identical output, which is the foundation of a clean CI gate. Pair with a pre-commit hook so PRs arrive already formatted, focusing review on logic.

idempotent

Gradle Kotlin DSL

Tidy build.gradle.kts files pasted from blogs. Pairs with EditorConfig + .prettierrc for end-to-end consistency. Whitespace-only changes vanish so reviewers see real diffs, and git blame stays honest about who wrote what.

CI-ready

Gist cleanup

Make Kotlin samples from articles readable. Output respects your indent width, tab style, and print-width — settings carry over for repeat runs. Switching 2-space to 4-space costs nothing in CPU but standardises an entire codebase.

diff-clean

Code review

Strip whitespace churn so diffs show real changes. Format-on-save is the fastest feedback loop; CI is the safety net. Together they make inconsistent indentation a thing of the past and free up review cycles for genuine concerns.

PR-friendly

Quick fix

Reformat without opening Android Studio. Whitespace-only changes don't trigger downstream content-hash invalidations, so CDN cache keys and CI cache layers stay warm. Real changes get all the rebuild budget.

review-ready

Docs examples

Standardise Kotlin examples for documentation. Pairs with linters (ESLint, Stylelint, pylint) that catch what formatting alone can't — bugs, unused imports, dead code. Each tool stays in its lane, and the codebase stays clean.

deterministic
FAQ

Frequently asked questions

No — it's a brace-tracking indenter. Use ktlint or detekt for real rule-based formatting.
Trailing lambda braces are counted normally and indented as a block.
Strings (including $-templates) are scanned and skipped when counting braces.
No — annotations stay on their original lines; only indentation changes.
No — the formatter runs locally in your browser tab.
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