Code Formatters

📝 Course Notes

Key knowledge points from this lesson:

OpenCode automatically uses language-specific formatters after files are written or edited. This ensures that generated code follows your project's code style.

Built-in Formatters

OpenCode includes built-in formatters for many popular languages and frameworks:

Formatter	Extensions	Requirements
gofmt	.go	gofmt command available
mix	.ex, .exs, .eex, .heex, .leex, .neex, .sface	mix command available
prettier	.js, .jsx, .ts, .tsx, .html, .css, .md, .json, .yaml, etc.	prettier dependency in package.json
biome	.js, .jsx, .ts, .tsx, .html, .css, .md, .json, .yaml, etc.	biome.json(c) config file exists
zig	.zig, .zon	zig command available
clang-format	.c, .cpp, .h, .hpp, .ino, etc.	.clang-format config file exists
ktlint	.kt, .kts	ktlint command available
ruff	.py, .pyi	ruff command available and configured
rustfmt	.rs	rustfmt command available
uv	.py, .pyi	uv command available
rubocop	.rb, .rake, .gemspec, .ru	rubocop command available
standardrb	.rb, .rake, .gemspec, .ru	standardrb command available
htmlbeautifier	.erb, .html.erb	htmlbeautifier command available
air	.R	air command available
dart	.dart	dart command available
ocamlformat	.ml, .mli	ocamlformat command available and .ocamlformat config exists
terraform	.tf, .tfvars	terraform command available
gleam	.gleam	gleam command available
nixfmt	.nix	nixfmt command available
shfmt	.sh, .bash	shfmt command available
oxfmt (experimental)	.js, .jsx, .ts, .tsx	oxfmt dependency in package.json and experimental env var enabled

If your project has prettier in its package.json, OpenCode will automatically use it.

How It Works

When OpenCode writes or edits a file:

1. Checks all enabled formatters based on file extension
2. Runs the appropriate formatting command
3. Automatically applies formatting changes

This process happens in the background, ensuring code style is maintained without manual intervention.

Configuration

Customize formatters through the formatter section in your config file:

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

Each formatter configuration supports the following options:

Property	Type	Description
disabled	boolean	Set to true to disable this formatter
command	string[]	Formatting command
environment	object	Environment variables when running the formatter
extensions	string[]	File extensions this formatter handles

Disabling Formatters

Globally disable all formatters:

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

Disable a specific formatter:

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

Custom Formatters

You can override built-in formatters or add new ones:

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

The $FILE placeholder in the command will be replaced with the path of the file being formatted.

Related Resources

• LSP Servers - Code intelligence support
• Configuration Reference - Complete configuration options