Lesson 17Memory

Modular Rules

Path-specific instructions

What are Modular Rules

Modular rules are separate .md files in the .claude/rules/ directory that apply only to specific files.

.claude/rules/
├── typescript.md       # Rules for *.ts, *.tsx
├── react.md           # Rules for components
├── api.md             # Rules for API routes
├── tests.md           # Rules for tests
├── security.md        # Security guidelines
└── database.md        # Database conventions

💡 Rules are automatically loaded when Claude works with files matching the patterns.

Rule Format

Each rule is a Markdown file with YAML frontmatter containing paths:

---
paths:
  - "**/*.ts"
  - "**/*.tsx"
  - "!**/*.test.ts"
---

# TypeScript Rules

Your instructions here...

Include patterns

**/*.ts — all TS files
src/components/** — all in components
*.config.js — configs at root

Exclude patterns

!**/*.test.ts — except tests
!**/node_modules/** — except modules
!dist/** — except dist

Example Rules

typescript.md

**/*.ts**/*.tsx

---
paths:
  - "**/*.ts"
  - "**/*.tsx"
---

# TypeScript Rules

- Use strict TypeScript settings
- Prefer interfaces over types for objects
- Always add return types to functions
- Use 'unknown' instead of 'any'

react.md

src/components/**/*.tsx

---
paths:
  - "src/components/**/*.tsx"
---

# React Component Rules

- Use functional components only
- Props interface should be named {ComponentName}Props
- Use memo() for expensive renders
- Prefer composition over prop drilling

api.md

src/app/api/**/*.ts

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

# API Route Rules

- Always validate request body with Zod
- Return proper HTTP status codes
- Handle errors with try/catch
- Log all errors to monitoring

tests.md

**/*.test.ts**/*.spec.ts

---
paths:
  - "**/*.test.ts"
  - "**/*.spec.ts"
---

# Testing Rules

- Use describe/it blocks
- Mock external dependencies
- Test edge cases
- Aim for 80% coverage

When Rules Apply

Claude reads a file → Rules for this file type are loaded

Claude edits a file → Rules are applied when generating code

Claude creates a new file → Rules determined by extension/path

Best Practices

1.Create separate rules for different file types
2.Use exclusions (!) for tests and generated files
3.Document "why", not just "what"
4.Commit rules to git with the project

This lesson is part of a structured LLM course.

My Learning Path