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Configure Biome

src/content/docs/guides/configure-biome.mdx

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import { FileTree } from '@astrojs/starlight/components';

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

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:

json
{
  "$schema": "https://biomejs.dev/schemas/2.3.11/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.

json5
{
  "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

Biome supports the following configuration files, in the following order:

  1. biome.json
  2. biome.jsonc
  3. .biome.json
  4. .biome.jsonc

Biome attempts to discover the configuration file in the following order:

  1. The current working directory
  • From the CLI, the working directory is where the command is executed
  • From the editor, the working directory is the root of the project
  1. Parent folders, recursively
  2. The home directory, which depends on your operative system:
  • $XDG_CONFIG_HOME or $HOME/.config/biome on Linux
  • /Users/$USER/Library/Application Support/biome on macOS
  • C:\Users\$USER\AppData\Roaming\biome\config on Windows

If no configuration is found, Biome's default configuration is used.

Here's an example:

<FileTree> - app/ - backend/ - biome.json - package.json - frontend/ - legacy/ - package.json - new/ - package.json - biome.json </FileTree>
  • 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;

:::note Biome supports nested biome.json files. For more information, read Use Biome in big projects. :::

Specifying files to process

You can control the files/folders to process using different strategies, either CLI, configuration and VCS.

:::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 :::

Include files via CLI

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.

shell
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 **. :::

Control files via configuration

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.

Include files via configuration

Let's take the following configuration, where we want to include only JavaScript files (.js) that are inside the src/ folder, the test/ folder, and ignore files that have .min.js in their name:

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

And run the following command:

shell
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.

shell
biome lint test/

:::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. :::

Exclude files via configuration

If you want to exclude files and folders from being processed by Biome, you can use the files.includes configuration and use the negated patterns:

  • use of the leading ! to ignore files from being linted/formatted
  • use of the double leading !! to ignore files from any project-related operation

Project-related operations are:

  • Construction of the internal module graph, so that some project rules can resolve information from imports and exports.
  • Inference of types, so that type-aware lint rules can correct infer types.

A file that is considered for project-related operations is indexed.

Before listing the negated globs, they must be preceded by the ** pattern.

In the following example, we tell Biome to include all files, except:

  • dist/ folder, which will be ignored from any project-related operation, hence they aren't indexed.
  • Any file that ends .generated.js, which are ignored from formatting and linting, by are still indexed.
json
{
  "files": {
    "includes": [
      "**",
      "!**/*.generated.js",
      "!!**/dist"
    ]
  }
}

For more information on how interact with scanner and how it indexes your files, check the relative reference page

Control files via VCS

You can ignore files ignored by your VCS.

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
  • .oxlintrc.json
  • .swcrc
  • api-documenter.json
  • api-extractor.json
  • babel.config.json
  • deno.json
  • devcontainer.json
  • dprint.json
  • jsconfig.json
  • jsr.json
  • language-configuration.json
  • nx.json
  • project.json
  • tsconfig.json
  • typedoc.json
  • typescript.json
  • All .json files under the $PROJECT/.vscode/* folder and under the user VS Code settings folder
  • All .json files under the $PROJECT/.zed/* folder and under the user Zed settings folder
  • All .json files under the $PROJECT/.cursor/* folder and under the user Cursor settings folder