Migrate from ESLint and Prettier

Biome can automatically migrate your existing ESLint and Prettier configuration files to the equivalent biome.json file. Run one or both commands according to your project:

biome migrate eslint --write
biome migrate prettier --write

To understand what changes when you switch tools, see Comparison with other tools.

Migrate from ESLint

biome migrate eslint ports the rules, globals, overrides, and ignore patterns from your ESLint configuration. It reads both legacy and flat configuration files, follows extends, loads shared and plugin configurations, and migrates .eslintignore.

Given the following ESLint configuration:

.eslintrc.json

{
  "globals": {
    "Global1": "readonly"
  },
  "rules": {
    "eqeqeq": "error",
    "no-var": "error"
  },
  "overrides": [
    {
      "files": ["tests/**"],
      "rules": {
        "eqeqeq": "off"
      }
    }
  ]
}

Run the following command to migrate it:

npm

npx biome migrate eslint --write

pnpm

pnpm biome migrate eslint --write

bun

bunx biome migrate eslint --write

deno

deno run -A npm:@biomejs/biome migrate eslint --write

yarn

yarn biome migrate eslint --write

The command produces the following biome.json:

biome.json

{
"$schema": "https://biomejs.dev/schemas/2.5.15/schema.json",
"vcs": { "enabled": false, "clientKind": "git", "useIgnoreFile": false },
"files": { "ignoreUnknown": false },
"formatter": { "enabled": true, "indentStyle": "tab" },
"linter": {
  "enabled": true,
  "rules": {
    "preset": "none",
    "suspicious": { "noDoubleEquals": "error", "noVar": "error" }
  }
},
"javascript": {
  "formatter": { "quoteStyle": "double" },
  "globals": ["Global1"]
},
"overrides": [
  {
    "includes": ["tests/**"],
    "linter": { "rules": { "suspicious": { "noDoubleEquals": "off" } } }
  }
],
"assist": {
  "enabled": true,
  "actions": { "source": { "organizeImports": "on" } }
}
}

The command replaces the linter settings in your existing biome.json. It sets the rule preset to none and enables only the rules it migrated. Review the result before relying on it.

Inspired rules

Each Biome rule is either identical to its ESLint source or only inspired by it, as listed on the Rule sources page. By default, the command migrates identical rules only. Pass the --include-inspired flag to migrate inspired rules as well:

npm

npx biome migrate eslint --write --include-inspired

pnpm

pnpm biome migrate eslint --write --include-inspired

bun

bunx biome migrate eslint --write --include-inspired

deno

deno run -A npm:@biomejs/biome migrate eslint --write --include-inspired

yarn

yarn biome migrate eslint --write --include-inspired

Even with inspired rules, the result does not behave exactly like ESLint, because some rule options are not implemented and some rules deliberately differ. See Rules and compatibility for the differences.

Cyclic references

Some plugins and shared configurations export objects with cyclic references, which Biome cannot load. If the migration fails with such an error, comment out the plugins and shared configurations, run the migration, then restore them one at a time to find the one responsible:

eslint.config.js

import { defineConfig } from 'eslint';
import jsxA11y from 'eslint-plugin-jsx-a11y';
import react from '@eslint-react/eslint-plugin';
import stylistic from '@stylistic/eslint-plugin';
import tsEslint from 'typescript-eslint';

export default defineConfig([
  react.configs.recommended,
  jsxA11y.flatConfigs.recommended,
  // react.configs.recommended,
  // jsxA11y.flatConfigs.recommended,
  {
    plugins: {
      '@stylistic': stylistic,
      '@typescript-eslint': tsEslint.plugin,
      // '@stylistic': stylistic,
      // '@typescript-eslint': tsEslint.plugin,
    },
  }
]);

Once the migration is done, configure the rules from those plugins by hand in biome.json.

Migrate from Prettier

biome migrate prettier ports the options from your Prettier configuration and the patterns from .prettierignore.

Biome’s formatter defaults differ from Prettier’s, so the command writes every option explicitly to keep your current output. See Output and compatibility for the differences that remain.

Given the following Prettier configuration:

.prettierrc.json

{
  "useTabs": false,
  "singleQuote": true,
  "overrides": [
    {
      "files": ["*.json"],
      "options": { "tabWidth": 2 }
    }
  ]
}

Run the following command to migrate it:

npm

npx biome migrate prettier --write

pnpm

pnpm biome migrate prettier --write

bun

bunx biome migrate prettier --write

deno

deno run -A npm:@biomejs/biome migrate prettier --write

yarn

yarn biome migrate prettier --write

The command produces the following biome.json:

biome.json

{
"$schema": "https://biomejs.dev/schemas/2.5.15/schema.json",
"vcs": { "enabled": false, "clientKind": "git", "useIgnoreFile": false },
"files": { "ignoreUnknown": false },
"formatter": {
  "enabled": true,
  "formatWithErrors": false,
  "indentStyle": "space",
  "indentWidth": 2,
  "lineEnding": "lf",
  "lineWidth": 80,
  "attributePosition": "auto",
  "bracketSameLine": false,
  "bracketSpacing": true,
  "expand": "auto",
  "useEditorconfig": true
},
"linter": { "enabled": true, "rules": { "preset": "recommended" } },
"javascript": {
  "formatter": {
    "jsxQuoteStyle": "double",
    "quoteProperties": "asNeeded",
    "trailingCommas": "all",
    "semicolons": "asNeeded",
    "arrowParentheses": "always",
    "bracketSameLine": false,
    "quoteStyle": "single",
    "attributePosition": "auto",
    "bracketSpacing": true
  }
},
"html": {
  "formatter": {
    "indentScriptAndStyle": false,
    "selfCloseVoidElements": "always"
  }
},
"overrides": [{ "includes": ["*.json"], "formatter": { "indentWidth": 2 } }],
"assist": {
  "enabled": true,
  "actions": { "source": { "organizeImports": "on" } }
}
}

After migrating

ESLint and Prettier skip the files in your .gitignore by default. Biome does so only when its VCS integration is enabled, so enable it to keep the same set of files ignored.

Once you are satisfied with the result, remove ESLint, Prettier, and their plugins from your dependencies, and replace their editor extensions with Biome’s.