Formatting

bun fmt uses the native OXC formatter embedded in Bun. It does not install an npm package or launch a formatter subprocess. JavaScript, TypeScript, JSX and JSON use the selected native formatters. A format requiring an unavailable plugin fails explicitly.

bun fmt src
bun fmt --check src
bun fmt --write src
bun fmt --ignore-pattern 'fixtures/**' src

With no filesystem operands, Bun examines the working directory. --check writes nothing and exits with code 1 when formatting differs. Without --check, it writes formatted files. Filesystem discovery excludes generated dependency directories and protected stores; explicit protected or parent-traversing paths are rejected.

Native discovery reads nested .gitignore files consistently for implicit and explicit roots. A Prettier configuration instead selects Prettier's case-insensitive working-directory ignore files. An explicit --ignore-path replaces the native default Gitignore search. Explicit symbolic-link operands fail with code 2 without following or writing their targets.

Format standard input

--stdin-filepath supplies a virtual name to select the parser. Bun reads UTF-8 source from standard input and writes formatted source to standard output. It never opens or writes the virtual file. Input is bounded to 8 MiB.

printf 'const answer=42' | bun fmt --stdin-filepath input.ts
printf 'const answer=42' | bun fmt --stdin-filepath input.ts --check

In this mode --check produces no source output and returns 1 on a difference. --write alone still prints formatted standard input; it never writes the virtual file. Filesystem operands and repeated virtual-name options are rejected. Invalid UTF-8, syntax, unsupported formats and invalid options return code 2. The virtual filename selects configuration discovery. Pass --config to choose project formatting options explicitly.

Configuration

Filesystem formatting discovers .oxfmtrc.json or .oxfmtrc.jsonc and .editorconfig through the native formatter. -c or --config selects an explicit configuration.

{
  "printWidth": 120,
  "semi": true,
  "singleQuote": false
}

bun fmt --config .oxfmtrc.json src

The native CLI accepts --check, --write, --stdin-filepath, --config and --ignore-pattern. Other native options fail explicitly. Workspace selection, Git-ref selection and external formatter options are not inferred from these flags.

Use bun lint for lint diagnostics and fixes.