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Kotlin Code Formatter

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クライアント側

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Kotlin Code Formatter

Paste any Kotlin source and get a clean, ktlint-style reformat in your browser. The formatter normalizes indentation, fixes operator spacing, sorts imports, and adds trailing commas in multi-line lists, all without sending code to a server.

使用方法

Paste your Kotlin code into the input box, or click 例を試してみてください。 to load a sample file.
Pick the indent size (2 spaces, 4 spaces, or tabs) and the maximum line width.
トグル インポートの並べ替え と Add trailing commas based on your style preference.
クリック形式 and copy or download the cleaned-up output.

機能

設定可能なインデント – switch between 2 spaces, 4 spaces, or tabs without re-editing the file.
Operator spacing – consistent whitespace around =, ==, ===, ->, ?:, and compound assignments.
Import sorting – alphabetical ordering of import declarations as a single block.
Trailing commas – automatically appended in multi-line argument and parameter lists.
Brace placement – opening braces stay on the same line as their declaration, matching Kotlin conventions.
String & comment safety – tokens inside string literals, KDoc, and block comments are preserved verbatim.
クライアントサイドのみ – your code never leaves the browser; no upload, no logs.
コピー・ダウンロード – grab the result as text or save it as a .kt ファイル。

When This Tool Helps

This formatter is built for situations where running a full ktlint or ktfmt toolchain is overkill: pasting a snippet from a chat or pull-request thread, cleaning up a one-off Gist, or normalizing a sample for documentation. It applies the rules that bite most often in code review – inconsistent spacing around colons, missing blank lines between top-level declarations, mismatched indent levels after an edit – and leaves the deeper semantic transforms to the IDE.

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 よくある質問

What style guide does Kotlin code formatting follow?

Kotlin code formatting is guided by the official Kotlin coding conventions published by JetBrains. The conventions cover indentation (four spaces, no tabs), brace placement on the same line as the declaration, trailing commas in multi-line lists, and the canonical ordering of modifiers like public, open, override, and suspend. Tools such as ktlint and ktfmt enforce variants of these rules so that codebases stay consistent across teams.
How are Kotlin imports organized?

Kotlin imports are typically grouped into a single block at the top of the file directly below the package declaration, with no blank lines between imports. The convention is to sort imports alphabetically by their full path. Star imports are allowed but discouraged for ambiguous packages; star imports for kotlinx.android.synthetic and similar generated packages are common exceptions.
Why are trailing commas useful in Kotlin?

Trailing commas in multi-line argument lists, parameter lists, and collection literals reduce diff noise when items are added or reordered, because the line above the closing bracket does not need to be edited just to add a comma. Kotlin 1.4 made trailing commas a first-class part of the language grammar, and ktlint encourages them in lists that span more than one line.
How does Kotlin handle line length and wrapping?

Kotlin's official guide recommends a soft maximum line length of one hundred to one hundred twenty characters. When a declaration exceeds the limit, parameters and chained method calls are typically broken onto separate lines with the continuation indented by one extra level. The opening brace stays on the same line as the closing parenthesis to keep declarations visually compact.