This file contains rules that apply to every automated contribution. Detailed workflows live in .claude/skills/ or the contributing guides they reference.

• Keep responses short, factual, and technical.
• Do not use emojis in source, comments, rustdoc, diagnostics, tests, snapshots, commits, issues, PR communication, or agent output. The PR-title marker above is the only exception.
• Do not claim a Biome function, module, behavior, or convention exists without an exact file and line, a source excerpt, or a reproducible command.
• If evidence is unavailable, state that rather than presenting the claim as fact.

• Read files in full before wide-ranging changes, before editing an unfamiliar file, and whenever the user requests an investigation or audit.
• Inspect the surrounding implementation and current contributing guide instead of copying remembered APIs or commands.
• Preserve unrelated worktree changes. Never revert or rewrite changes you did not make.

• Make the smallest change that satisfies the requested behavior.
• Add tests for code changes. Bug fixes require a case that fails without the fix.
• Run the narrowest relevant tests first, then broader checks when justified.
• Run the tests of the current crate to check possible regressions.
• Review generated snapshots as behavior, not disposable output.
• Run just f and just l before committing.

Load testing-codegen for test fixtures, snapshots, and generator selection.

Required generated artifacts:

If you change an .ungram file, run:

• just gen-grammar <lang>
• just gen-formatter --allow-dirty

If you change the name of a lint rule or assist action, run:

• just gen-rules
• just gen-configuration

Bindings and other full analyzer outputs may be left to the CI Autofix job unless they are needed for local verification.

After implementation, code generation, formatting, linting, and tests, review the complete change with biome-code-review.

• Use a fresh subagent when one is available.
• Provide only the review scope and intended business requirements. Do not include suspected defects, implementation hints, prior findings, or expected outcomes.
• Resolve actionable findings and rerun affected verification.
• Repeat the review when fixes materially change the implementation.

Before opening a PR, explicitly confirm whether the change is user-facing. User-facing behavior requires a changeset; internal refactors, tests, CI, and documentation-only changes do not.

For a user-facing change, load changeset to choose the release level and create or edit the entry. Branch targeting and changeset policy are canonical in CONTRIBUTING.md.

• Do not write PR descriptions or contributor communication. CONTRIBUTING.md requires the contributor to author that prose.
• Preserve .github/PULL_REQUEST_TEMPLATE.md; never replace or bypass it.
• If opening a PR from user-provided text, ensure it discloses the extent of AI assistance.
• Use a conventional-commit title and the target branch defined in CONTRIBUTING.md.

Load doc-comments whenever editing //, ///, or //! comments, including comments added incidentally.

• Write for a contributor reading the code at HEAD without access to the conversation, issue, PR, or diff.
• State contracts in ///, module rationale and terminology in //!, and non-obvious rationale in //.
• Do not narrate change history or address reviewers.
• Delete comments that only restate names, types, or control flow.
• Rustdoc inside declare_lint_rule! and declare_assist_rule! is end-user documentation; also load the lint-rule guide for its content requirements.

Internal biome_* crates under [dev-dependencies] use path = "../biome_*", not workspace = true. Regular [dependencies] continue to use workspace = true.

The skill catalog and trigger boundaries are maintained in .claude/skills/README.md. Load only the skills relevant to the current task.