Biome Knowledge Patch

Biome Knowledge Patch

Use this skill when configuring, migrating, running, or integrating Biome and the requested work touches the behaviors summarized here. Read the topic guide that matches the task before changing configuration or recommending a command.

Topic index

Breaking changes and migrations

Rule presets

Use linter.rules.preset instead of the deprecated linter.rules.recommended. The "all" preset selects all stable rules but still excludes nursery rules; "recommended" preserves the former recommended selection. Update an existing configuration with:

biome migrate --write

Object-form rule configuration

Include level whenever a rule uses object form. Omitting it is a configuration error:

{ "linter": { "rules": { "suspicious": { "noConsole": { "level": "warn" } } } } }

An optionless rule object needs only level; do not add an "options": null property.

Scanner ignores

Replace deprecated files.experimentalScannerIgnores with !! force-ignore patterns in files.includes. A force-ignore stops traversal and indexing; a single ! only excludes processing and can still allow project analysis to index an imported file.

{
  "files": {
    "includes": ["**", "!**/*.test.js", "**/special.test.js", "!!**/dist"]
  }
}

Override selection

Only the first matching overrides entry applies. Put specific patterns before broader patterns:

{
  "overrides": [
    { "includes": ["src/generated/**"], "formatter": { "enabled": false } },
    { "includes": ["src/**"], "formatter": { "lineWidth": 100 } }
  ]
}

Renamed formatter and lint settings

• Use javascript.formatter.trailingCommas and --trailing-commas; the singular trailingComma and --trailing-comma names are deprecated.
• Replace correctness/noInvalidNewBuiltin with correctness/noInvalidBuiltinInstantiation.
• Replace style/useSingleCaseStatement with correctness/noSwitchDeclarations.
• Replace suspicious/noConsoleLog with suspicious/noConsole.
• Stable-rule promotion renamed noFloatingClasses to noUnusedInstantiation, noMultiStr to noMultilineString, useFind to useArrayFind, and useSpread to useSpreadOverApply.

Removed and relocated rules

Do not configure the removed nursery rule useAnchorHref; useValidAnchor covers its use case. Domain-specific rules are not enabled merely by enabling their rule group. They require a matching dependency, an explicit domain, or explicit rule configuration.

Configuration quick reference

Monorepo roots and inheritance

Each configuration is a root by default. For a nested configuration, set "root": false or use "extends": "//"; the latter inherits the monorepo root and implies root: false.

{
  "extends": "//",
  "formatter": { "enabled": false }
}

Array-form extends entries run from least to most relevant. Extended files cannot extend other files, and paths inside shared configuration resolve relative to the configuration that extends it.

Tool-specific file scopes

Apply linter.includes, formatter.includes, and assist.includes after files.includes. They can narrow the initial file set but cannot add files back. Configure assist scope and recommended source actions separately from linting and formatting.

CLI quick reference

Focus checks

Repeat --only and --skip to select rules, groups, domains, assist actions, or plugins where the command supports them. --skip takes precedence.

biome check --only=suspicious/noDebugger src
biome ci --skip=project src

Selecting a disabled rule enables it at error when recommended and warn otherwise. Selecting a group enables only its recommended preset. Nursery is also a valid selector.

Staged and watched files

--staged selects files in the Git index, but Biome reads the current working tree contents of each selected file rather than an isolated index snapshot.

biome check --staged .

Read-only lint, format, and check commands accept --watch. Do not combine watch mode with --fix or --write.

biome check --watch .

Diagnostics and reports

Use --max-diagnostics=none for no cap. A non-default reporter also lifts the cap. --reporter is repeatable, and a neighboring --reporter-file sends that reporter to a file.

biome ci --reporter=default --reporter=rdjson --reporter-file=./reports/report.json

Available outputs described in the reference include JSON, summary, GitHub, GitLab, JUnit, Checkstyle, RDJSON, SARIF, and concise diagnostics.

Linting quick reference

Domains and project analysis

Use linter.domains with "recommended", "all", or "none". Recommended excludes nursery rules; all includes them. Project and type domains scan the whole project and can materially increase lint time.

{
  "linter": {
    "domains": { "project": "all", "types": "all" }
  }
}

The project domain supplies module-graph rules. The types domain enables type inference; its covered rules are nursery rules and therefore require "types": "all", not "recommended".

Fix applicability

Object-form rule configuration accepts fix: "none", "safe", or "unsafe" to disable actions or override applicability. Applying safe or unsafe fixes through biome check also formats the result.

Formatting and language quick reference

Expansion and final newlines

formatter.expand and JavaScript- or JSON-specific overrides accept "auto", "always", or "never". In auto mode, an existing first-property line break keeps an object multiline while fitting arrays collapse. package.json behaves as always unless explicitly configured.

formatter.trailingNewline defaults to true; set it globally or per language to false to remove the final newline.

HTML and embedded content

The HTML formatter must be enabled explicitly. Embedded JavaScript and CSS use their own formatter settings. html.formatter.indentScriptAndStyle defaults to false and controls indentation inside <script> and <style> blocks.

Enable javascript.experimentalEmbeddedSnippetsEnabled to format and lint recognized CSS, GraphQL, and Relay-tagged snippets in JavaScript template literals.

Import organization and other assists

Import organization is an assist rather than a lint diagnostic. It can move imports across ordinary blank lines, merge same-module imports, sort attributes and exports, and honor detached-comment boundaries. Consult the formatting reference for other structural-sorting assists.

GritQL quick reference

Run experimental structural searches with biome search. Quote a query that contains GritQL backticks with shell single quotes when backticks would be interpreted as command substitution.

biome search '`console.$method($args)` where { $method <: or { `log`, `info` } }' ./

Top-level plugins entries load .grit lint patterns. Plugins can register diagnostics, target supported languages, restrict execution with includes, and attach safe or unsafe rewrites. Read the plugin guide before authoring or changing a pattern.

Editor note

Go-to-definition is disabled by default as of 2.5.1 because enabling it builds the module graph and could cause memory leaks when Biome starts in a home directory. Re-enable it in the Biome extension settings only when needed.