Writing Rules

Rules are constraints Claude follows automatically when working with matching files. They live in .claude/rules/ or a plugin's rules/ directory.

Structure

---
paths:
  - "src/api/**/*.ts"
  - "**/*.test.ts"
---

Declarative constraints here.

Path Patterns

• **/*.ts — all TypeScript files
• src/**/* — everything under src/
• {src,lib}/**/*.ts — multiple directories
• Omit paths entirely for rules that apply everywhere

Rules without paths load every session. Rules with paths only load when Claude works with matching files.

Writing Constraints

Be declarative — state what should/shouldn't be done, not step-by-step procedures.

Be specific — "Use 2-space indentation" not "format properly."

Skip the obvious — don't restate best practices Claude already knows. Only specify what's unique to your project.

One topic per file — testing.md, security.md, not everything.md. Organize with subdirectories for grouping.

Provide alternatives — never write "Don't do X" without saying what to do instead.

When to Use Rules vs Other Tools

• Rules: File-type-specific conventions that are advisory (Claude should follow but there's no hard enforcement)
• CLAUDE.md: Universal project context loaded every session
• Hooks: Must be enforced deterministically — cannot be ignored
• Skills: Reference material loaded on-demand, not automatically

Anti-Patterns

• Procedural instructions (use commands or skills instead)
• Rules that apply to every file type (use CLAUDE.md or omit paths)
• Duplicating CLAUDE.md content
• Over-broad path patterns that match unrelated files
• Rules longer than ~30 lines (split into multiple files or use a skill)