Configure Biome

This guide will help you to understand how to configure Biome. It explains the structure of a Biome configuration file and how Biome resolves its configuration. If you are already familiar with the configuration, you may want to take a look at the configuration reference, which details all the options available.

Biome allows you to customize its behavior using CLI options or a configuration file named biome.json or biome.jsonc. We recommend that you create a configuration file for each project. This ensures that each team member has the same configuration in the CLI and in any editor that allows Biome integration. Many of the options available in a configuration file are also available in the CLI.

Configuration file structure

Section titled Configuration file structure

A Biome configuration file is named biome.json or biome.jsonc. It is usually placed in your project’s root folder, next to your project’s package.json.

Because Biome is a toolchain, its configuration is organized around the tools it provides. At the moment, Biome provides three tools: the formatter, the linter and the assist. All of these tools are enabled by default. You can disable one or several of them using the <tool>.enabled field:

biome.json

{
  "$schema": "https://biomejs.dev/schemas/2.0.0-beta/schema.json",
  "formatter": {
    "enabled": false
  },
  "linter": {
    "enabled": false
  },
  "assist": {
    "enabled": false
  }
}

Options that apply to more than one language are placed in the corresponding tool field. Language-specific options of a tool are placed under a <language>.<tool> field. This also allows overriding general options for a given language. You can also enable or disable a tool based on the language. In the following example, we configure the general options formatter.indentStyle and formatter.lineWidth for all the languages. Also, we set the JavaScript-specific option quoteStyle in javascript.formatter and we override formatter.lineWidth. We disabled the formatter for JSON files.

biome.jsonc

{
  "formatter": {
    "indentStyle": "space", // default is `tab`
    "lineWidth": 100 // default is `80`
  },
  "javascript": {
    "formatter": {
      "quoteStyle": "single", // default is `double`
      "lineWidth": 120 // override `formatter.lineWidth`
    }
  },
  "json": {
    "formatter": {
      "enabled": false
    }
  }
}

Note

Biome refers to all variants of the JavaScript language as javascript. This includes TypeScript, JSX and TSX.

Configuration file resolution

Section titled Configuration file resolution

Biome uses auto discovery to find the nearest configuration file. It looks in the working directory and its parent folders until it finds a biome.json or a biome.jsonc file. If no configuration is found, Biome’s default configuration is used. If both biome.json and biome.jsonc are present in the same folder, biome.json is used.

Here’s an example:

• Directoryapp/

  • Directorybackend/

    • biome.json
    • package.json
  • Directoryfrontend/

    • Directorylegacy/

      • package.json
    • Directorynew/

      • package.json
    • biome.json

• Biome commands that run in app/backend/package.json will use the configuration file app/backend/biome.json;
• Biome commands that run in app/frontend/legacy/package.json and app/frontend/new/package.json will use the configuration file app/frontend/biome.json;

Caution

Biome doesn’t yet support nested biome.json files, neither in CLI nor in LSP. Follow and help the support in the related issue

Specifying files to process

Section titled Specifying files to process

The first way to control which files and folders are processed by Biome is to list them in the CLI. In the following command, we only format file1.js and all the files in the src folder, because folders are recursively traversed.

biome format file1.js src/

Caution

Glob patterns used on the command line are not interpreted by Biome. They are expanded by your shell. Some shells don’t support the recursive glob **.

The Biome configuration file can be used to refine which files are processed. You can explicitly list the files to be processed using the files.includes field. files.includes accepts glob patterns such as src/**/*.js. Negated patterns starting with ! can be used to exclude files.

Paths and globs inside Biome’s configuration file are resolved relative to the folder the configuration file is in. An exception to this is when a configuration file is extended by another.

files.includes applies to all of Biome’s tools, meaning the files specified here are processed by the linter, the formatter and the assist, unless specified otherwise. For the individual tools, you can further refine the matching files using <tool>.includes.

Caution

The global files.includes has slightly different semantics than the more specific <tool>.includes fields. Any file or folder that doesn’t match files.includes is excluded from use by any of Biome’s tools. This means that any tool-specific includes field can never match a file that doesn’t also match files.includes.

Let’s take the following configuration:

biome.json

{
  "files": {
    "includes": ["src/**/*.js", "test/**/*.js", "!**/*.min.js"],
  },
  "linter": {
    "includes": ["!test/**"]
  }
}

And run the following command:

biome format test/

The command will format the files that end with the .js extension and don’t end with the .min.js extension from the test/ folder. The files in src/ are not formatted because the folder is not listed in the CLI.

If we run the following command, no files are linted because files inside the test/ folder are explicitly ignored for the linter.

biome lint test/

Note

By default, Biome always ignores some files that are said to be protected files. This means that no diagnostics will be ever emitted by Biome for those files. At the moment, the following files are protected:

• composer.lock
• npm-shrinkwrap.json
• package-lock.json
• yarn.lock

Note

You can also ignore files ignored by your VCS.

Well-known files

Section titled Well-known files

Here are some well-known files that we specifically treat based on their file names, rather than their extensions. Currently, the well-known files are JSON-like files only, but we may broaden the list to include other types when we support new parsers.

The following files are parsed as JSON files with both the options json.parser.allowComments and json.parser.allowTrailingCommas set to false.

• .all-contributorsrc
• .arcconfig
• .auto-changelog
• .bowerrc
• .c8rc
• .htmlhintrc
• .imgbotconfig
• .jslintrc
• .nycrc
• .tern-config
• .tern-project
• .vuerc
• .watchmanconfig
• mcmod.info

The following files are parsed as JSON files with the options json.parser.allowComments set to true but json.parser.allowTrailingCommas set to false. This is because the tools consuming these files can only strip comments.

• .ember-cli
• .eslintrc.json
• .jscsrc
• .jshintrc
• tslint.json
• turbo.json

The following files are parsed as JSON files with the options json.parser.allowComments and json.parser.allowTrailingCommas set to true. This is because the tools consuming these files are designed to accommodate such settings.

• .babelrc
• .babelrc.json
• .devcontainer.json
• .hintrc
• .hintrc.json
• .swcrc
• api-documenter.json
• api-extractor.json
• babel.config.json
• deno.json
• devcontainer.json
• dprint.json
• jsconfig.json
• jsr.json
• language-configuration.json
• tsconfig.json
• typedoc.json
• typescript.json

Sharing a configuration file

Section titled Sharing a configuration file

The extends field allows you to split your configuration across multiple files. This way, you can share common settings across different projects or folders.

Here’s an example of how you might set up your configuration to extend a common.json configuration file:

biome.json

{
  "extends": ["./common.json"]
}

The entries defined in extends are resolved from the path where the biome.json file is defined. They are processed in the order they are listed, with settings in later files overriding earlier ones.

Files that you extend from cannot extend other files in turn.

Note that paths in a configuration file are always resolved from the folder in which the biome.json/biome.jsonc file resides. When using the extends field, this means that paths in a shared configuration are interpreted from the location of the configuration that is extending it, and not from the folder of the file being extended.

For example, let’s assume a project that contains two directories backend/ and frontend/, each having their own biome.json that both extend a common.json configuration in the root folder:

• Directorybackend/

  • Directorysrc/

    • …
  • Directorytest/

    • …
  • biome.json
• Directoryfrontend/

  • Directorysrc/

    • …
  • Directorytest/

    • …
  • biome.json
• common.json

common.json

{
  "files": {
    "includes": ["src/**/*.js", "test/**/*.js"],
  },
  "linter": {
    "includes": ["!test/**"]
  }
}

frontend/biome.json

{
  "extends": ["../common.json"]
}

• When running Biome from the frontend/ folder, it will be configured to format and lint all JavaScript files in the frontend/src/ and frontend/test/ folders, and only format the files in the frontend/src/ folder. This works because the paths specified in common.json are interpreted from the frontend/ folder, because that’s where the biome.json file resides.
• Assuming backend/biome.json looks the same as frontend/biome.json, it will have the same behaviour, except the paths will be interpreted from the backend/ folder.

Exporting a Biome configuration from an NPM package

Section titled Exporting a Biome configuration from an NPM package

Biome is able to resolve configuration files from the node_modules/ folder. So you can export your configuration file from a package, and import it in multiple projects.

In order to do so, the first thing to do is to set up your “shared” Biome configuration in a certain way. Let’s suppose that you want to share a configuration from a package called @org/shared-configs, using the specifier @org/shared-configs/biome. You have to create an exports entry in the package.json of this package:

package.json

{
  "name": "@org/shared-configs",
  "type": "module",
  "exports": {
    "./biome": "./biome.json"
  }
}

Make sure that @org/shared-configs is correctly installed in your project, and update the biome.json file to look like the following snippet:

biome.json

{
  "extends": ["@org/shared-configs/biome"]
}

Biome will attempt to resolve your library @org/shared-configs/ from your working directory. The working directory is:

• when using the CLI, the folder where you execute your scripts from. Usually it matches the location of your package.json file;
• when using the LSP, the root folder of your project.

Caution

Paths starting with a dot . or ending with .json or .jsonc are always treated as relative paths, so they won’t be resolved from node_modules/.

For more information about the resolution algorithm, refer to the Node.js documentation.