# Formatting

> Format source with Bun's embedded native OXC core

`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.

```sh
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.

```sh
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.

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

```sh
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`](https://aphrody.app/docs/runtime/lint) for lint diagnostics and fixes.