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Dart Code Formatter

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Dart Code Formatter

Paste your Dart or Flutter source and instantly get a cleanly formatted version that follows the conventions enforced by dart format. The formatter runs entirely in your browser — no SDK install, no upload, and no waiting on a remote server. It is a fast, deterministic helper for every situation where you want spec-compliant output without leaving the page.

使用方法

Paste your Dart or Flutter code into the input area, or click 例を試してみてください。 to load a sample.
Pick your preferred indent size (2 spaces is the dart_style default, but 4 spaces and tabs are supported).
をドラッグして 行の長さ slider — the formatter will warn you about lines that exceed your target.
トグル Sort and group directives, 終端カンマを追加と、 Collapse blank lines as needed.
クリック形式 and copy or download the cleaned-up source.

機能

Configurable line length — slider from 40 to 160 characters, defaulting to the official 80.
dart_style-inspired indentation — supports 2 spaces, 4 spaces, or tabs.
Directive grouping — sorts and groups dart:, package:, and relative imports with a blank line between groups.
終端カンマ — adds a trailing comma to multi-line argument and parameter lists, exactly like Flutter widget trees expect.
Null-safety aware — preserves ?., !, ??と、 ??= with the correct spacing.
String-safe — single, double, triple, and raw (r"…") string literals are left untouched.
Comment-safe — line, block, and dartdoc (///) comments are preserved and reflowed cleanly.
Top-level spacing — inserts a blank line between top-level declarations for readability.
100%クライアントサイド — your code never leaves the browser, so it is safe for proprietary code.

ユースケース

Quick clean-up of a snippet pasted from a Stack Overflow answer or a chat message.
コードレビュー on GitHub or GitLab where you want to compare normalized output before commenting on style.
Onboarding new developers who do not yet have the Dart SDK installed locally.
Pre-commit sanity check when you want to compare your editor’s output to a second-opinion formatter.
Flutter widget trees where consistent trailing commas keep diff noise low.

 よくある質問

What style does the formatter follow?

The formatter mirrors the conventions enforced by dart format (the official tool from the Dart SDK), inspired by the dart_style package. It targets a default line length of 80 characters, applies two-space indentation, normalizes operator spacing, and groups directives in the canonical dart:, package:, then relative order.
Why are trailing commas important in Dart and Flutter?

A trailing comma at the end of a multi-line argument or parameter list tells the formatter to keep each element on its own line. In Flutter widget trees this dramatically improves readability and produces more meaningful diffs, so the official Dart style guide encourages trailing commas for any list that spans more than one line.
What is dart_style?

dart_style is the open-source Dart package that powers dart format, the IDE formatters in Android Studio, IntelliJ, and VS Code, and the formatter on dartpad.dev. It applies a deterministic, single-style algorithm so any two correctly-formatted Dart files look identical regardless of who wrote them.
How do null-safety operators like ??, ?., and ! affect formatting?

Null-aware operators are kept tight to their operands: ?. と ! never have surrounding spaces, while ?? と ??= behave like binary operators with a single space on each side. This matches the behavior of dart_style for sound null safety code.