Formatters

OpenCode can format files after its write, edit, or patch tools change them. Formatters are disabled by default, so enable them in your configuration:

opencode.jsonc

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": true,
}

Enable

Set formatter to true to enable every built-in formatter. OpenCode runs a built-in only when its executable and any project-specific requirements are available.

opencode.jsonc

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": true,
}

An object also enables the built-ins and lets you override them or add custom formatters. An empty object is therefore equivalent to true.

opencode.jsonc

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {},
}

Builtins

OpenCode includes these formatter definitions. Most require the named command to be available; definitions with extra detection rules list them below.

Formatter	Extensions	Requirement
`gofmt`	`.go`	`gofmt` command
`mix`	`.ex`, `.exs`, `.eex`, `.heex`, `.leex`, `.neex`, `.sface`	`mix` command
`oxfmt`	`.js`, `.jsx`, `.mjs`, `.cjs`, `.ts`, `.tsx`, `.mts`, `.cts`	`oxfmt` dependency in `package.json`
`prettier`	`.js`, `.jsx`, `.mjs`, `.cjs`, `.ts`, `.tsx`, `.mts`, `.cts`, `.html`, `.htm`, `.css`, `.scss`, `.sass`, `.less`, `.vue`, `.svelte`, `.json`, `.jsonc`, `.yaml`, `.yml`, `.toml`, `.xml`, `.md`, `.mdx`, `.graphql`, `.gql`	`prettier` dependency in `package.json`
`biome`	Same extensions as `prettier` above	`biome.json` or `biome.jsonc` and an installed `@biomejs/biome` binary
`zig`	`.zig`, `.zon`	`zig` command
`clang-format`	`.c`, `.cc`, `.cpp`, `.cxx`, `.c++`, `.h`, `.hh`, `.hpp`, `.hxx`, `.h++`, `.ino`, `.C`, `.H`	`clang-format` command and `.clang-format`
`ktlint`	`.kt`, `.kts`	`ktlint` command
`ruff`	`.py`, `.pyi`	`ruff` command and a Ruff config or dependency declaration
`air`	`.R`	`air` command that identifies itself as the R formatter
`uv`	`.py`, `.pyi`	`uv` command with `uv format` support
`rubocop`	`.rb`, `.rake`, `.gemspec`, `.ru`	`rubocop` command
`standardrb`	`.rb`, `.rake`, `.gemspec`, `.ru`	`standardrb` command
`htmlbeautifier`	`.erb`	`htmlbeautifier` command
`dart`	`.dart`	`dart` command
`ocamlformat`	`.ml`, `.mli`	`ocamlformat` command and `.ocamlformat`
`terraform`	`.tf`, `.tfvars`	`terraform` command
`latexindent`	`.tex`	`latexindent` command
`gleam`	`.gleam`	`gleam` command
`shfmt`	`.sh`, `.bash`	`shfmt` command
`nixfmt`	`.nix`	`nixfmt` command
`rustfmt`	`.rs`	`rustfmt` command
`pint`	`.php`	`laravel/pint` in `composer.json`
`ormolu`	`.hs`	`ormolu` command
`cljfmt`	`.clj`, `.cljs`, `.cljc`, `.edn`	`cljfmt` command
`dfmt`	`.d`	`dfmt` command

For example, enabling built-ins lets OpenCode discover and run a project-local Prettier dependency for matching files:

opencode.jsonc

{
  "formatter": true,
}

Customize

Add a named entry to change a built-in or define a custom formatter. A custom formatter needs both command and extensions to run.

opencode.jsonc

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {
    "prettier": {
      "environment": {
        "NODE_ENV": "development",
      },
      "extensions": [".js", ".ts"],
    },
    "deno-markdown": {
      "command": ["deno", "fmt", "$FILE"],
      "extensions": [".md"],
    },
  },
}

Field	Type	Behavior
`disabled`	`boolean`	Removes the named formatter when `true`.
`command`	`string[]`	Replaces the built-in command or defines a custom command.
`environment`	`Record<string, string>`	Adds environment variables while preserving the parent environment.
`extensions`	`string[]`	Replaces the built-in extension list or defines the custom list. Include the leading dot.

All fields are optional. A built-in entry inherits omitted values, while a new entry without a command or extensions cannot run.

opencode.jsonc

{
  "formatter": {
    "prettier": {
      "extensions": [".md", ".mdx"],
    },
  },
}

Commands

command is an argument array, not a shell command string. OpenCode replaces $FILE with the file’s absolute path and runs the command from the active project directory.

opencode.jsonc

{
  "formatter": {
    "custom": {
      "command": ["custom-fmt", "--write", "$FILE"],
      "extensions": [".custom"],
    },
  },
}

Matching

OpenCode compares the file’s final extension with extensions. Matching is case-sensitive, and compound entries such as .part.md do not match notes.part.md because its final extension is .md.

opencode.jsonc

{
  "formatter": {
    "markdown": {
      "command": ["deno", "fmt", "$FILE"],
      "extensions": [".md"],
    },
  },
}

When several formatters match, OpenCode tries them in registered order and stops after the first successful command. Built-ins retain their built-in order; custom entries follow in object order. If one exits unsuccessfully, OpenCode logs the failure and tries the next match.

opencode.jsonc

{
  "formatter": {
    "preferred": {
      "command": ["preferred-fmt", "$FILE"],
      "extensions": [".foo"],
    },
    "fallback": {
      "command": ["fallback-fmt", "$FILE"],
      "extensions": [".foo"],
    },
  },
}

Disable

Omit formatter or set it to false to disable all formatting. An explicit false can override a lower-priority configuration that enabled formatters.

opencode.jsonc

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": false,
}

To disable one built-in while leaving the others enabled, mark its named entry as disabled.

opencode.jsonc

{
  "formatter": {
    "prettier": {
      "disabled": true,
    },
  },
}