dart_format

A configurable formatter for Dart and Flutter. Like dart format / dartfmt, but you decide the rules — brace placement, spacing, trailing commas, indentation width, empty-line collapsing.

Keeps your line breaks. No forced wrapping at a line-length limit, no inserted or removed line breaks unless you explicitly enable an option that adds them.

Before	After

Why dart_format?

The built-in dart format is opinionated by design: you take its style or you don't. dart_format lets you decide.

It never wraps lines. No column limit, no automatic line breaks. Long lines stay long; short lines stay short. The only line breaks dart_format inserts are the ones you explicitly enable (e.g. addNewLineBeforeOpeningBrace). If you didn't ask for a break, you won't get one.

// dart format (built-in) — wraps at 80 columns
final user = User(
  name: 'Alice',
  email: 'alice@example.com',
  preferences: defaultPreferences,
);

// dart_format — keeps it on one line because you didn't ask for breaks
final user = User(name: 'Alice', email: 'alice@example.com', preferences: defaultPreferences);

It runs as a CLI, accepts source on stdin, and ships as a long-running HTTP service used by the JetBrains plugin and VS Code extension — so the same engine formats files from the terminal, your editor, and CI.

Configuration

Pass any subset as JSON via --config or --config-file. Missing keys fall back to the defaults below.

Option	Default	Controls
`addNewLineBeforeOpeningBrace`	`true`	`{` on its own line (Allman-style)
`addNewLineAfterOpeningBrace`	`true`	Body always on a new line
`addNewLineBeforeClosingBrace`	`true`	Closing `}` on its own line
`addNewLineAfterClosingBrace`	`true`	Newline after a block
`addNewLineAfterSemicolon`	`true`	One statement per line
`addNewLineAtEndOfText`	`true`	Trailing newline at end of file
`fixSpaces`	`true`	Normalise whitespace around tokens
`indentationSpacesPerLevel`	`4`	Indent width (`-1` = leave untouched)
`maxEmptyLines`	`1`	Collapse runs of blank lines (`-1` = leave)
`removeTrailingCommas`	`true`	Strip trailing commas

Example dartformat.json:

{
    "IndentationSpacesPerLevel": 2,
    "AddNewLineBeforeOpeningBrace": false,
    "RemoveTrailingCommas": false
}

dart_format --config-file=dartformat.json lib

Install

dart pub global activate dart_format

Or use one of the IDE integrations:

JetBrains (IntelliJ IDEA, Android Studio, …): https://plugins.jetbrains.com/plugin/21003-dartformat
VS Code: https://marketplace.visualstudio.com/items?itemName=eggnstone.DartFormat

Full install instructions: https://pub.dev/packages/dart_format/install

Quick start

# Format a single file
dart_format lib/main.dart

# Format every .dart file under lib/ and test/
dart_format lib test

# Glob (handy on Windows where the shell does not expand wildcards)
dart_format "lib/**/*.dart"

# CI / pre-commit: exits non-zero if any file would change
dart_format --check lib

# Pipe stdin to stdout (auto-detected when no positional args are given)
cat lib/main.dart | dart_format

CLI reference

Usage: dart_format [args] <file|dir|glob> [<file|dir|glob> ...]
    Positional inputs may be files, directories (recursed into *.dart),
    or glob patterns (e.g. "lib/**/*.dart").
    Pass `-` (or pipe stdin with no positional args) to format stdin to stdout.
    --check, -c                      No writes; exits non-zero if any file would change (for CI)
    --check-version                  Checks pub.dev for a newer dart_format release on start-up
    --config=<JSON>                  Inline configuration JSON (mutually exclusive with --config-file)
    --config-file=<PATH>             Path to a JSON config file (mutually exclusive with --config)
    --errors-as-json                 Writes errors as JSON to stderr
    --exclude=<GLOB>, -x <GLOB>      Excludes files matching the glob (repeatable)
    --help, -h                       Prints this help and exits
    --log-to-console[=true|false]    Logs to console
    --log-to-temp-file[=true|false]  Logs to a file in the system temp directory
    --port=<N>                       Port for web service mode (default: random free port, announced on stdout)
    --skip-version-check             Skips version check on start-up
    --version, -V                    Prints the version and exits
    --web                            Starts in web service mode

Exclude examples

# Exclude by file ending (repeatable)
dart_format lib --exclude="**/*.g.dart" --exclude="**/*.freezed.dart"

# Exclude a folder
dart_format lib --exclude="**/legacy/**"

# Exclude a specific file
dart_format lib --exclude="lib/generated_code.dart"

Default excludes

The following are always skipped during directory recursion and glob expansion. Pass an explicit file path to format one of them on purpose.

Folders: .dart_tool/, build/, and any hidden directory (.git/, .idea/, …).
Codegen suffixes: *.chopper.dart, *.config.dart, *.freezed.dart, *.g.dart, *.gen.dart, *.gr.dart, *.mocks.dart, *.pb*.dart, *.swagger.dart.

Security model

dart_format is designed for use on a single-user development machine. If that matches your environment, the defaults are fine. The notes below cover the cases where it doesn't.

Web mode (--web, used by the IDE plugins) binds only to 127.0.0.1 and isn't authenticated. Anything running on the same machine — including other local user accounts on a multi-seat box — can talk to your formatter. The service can't read your files; it can only format text the caller sends it. Don't expose it beyond loopback.
Browser hardening (2.2.0): the service rejects requests whose Host header isn't a loopback name, caps POST bodies at 4 MiB, and enforces a 60 s per-request wall-clock. That blocks the obvious DNS-rebinding and OOM-by-CSRF tricks a visited web page could play against 127.0.0.1.
Temp logging: in web mode, dart_format writes a session log to the system temp directory (filenames it touched, errors). Disable with --log-to-temp-file=false. CLI modes don't log unless --log-to-temp-file is passed.
Snapshot trust: dart_format is installed via dart pub global activate, which stores a compiled snapshot in the pub cache. Anyone who can write to that directory can replace the binary. Same caveat as every other pub-installed CLI.