How to create coding rules that Massu AI enforces through context injection and validation

Writing Custom Rules

Rules are the coding standards that Massu AI enforces in your project. When your AI assistant edits a file, applicable rules are automatically surfaced through the post-edit-context hook. Rules also power the massu_context and massu_validation_check tools.

Basic Rule Structure

Rules are defined in your massu.config.yaml:

yaml

rules:
  - pattern: "src/server/**/*.ts"
    severity: CRITICAL
    rules:
      - "All mutations must use protectedProcedure"
      - "Never expose raw error details to clients"
      - "Validate all inputs with Zod schemas"

Fields

Field	Required	Description
`pattern`	Yes	Glob pattern matching file paths
`severity`	No	CRITICAL, HIGH, MEDIUM, LOW
`rules`	Yes	Array of rule descriptions
`patternFile`	No	Path to detailed rule file in `.claude/`

Severity Levels

Level	When to Use	Hook Behavior
CRITICAL	Security issues, breaking changes	Always surfaced by post-edit-context
HIGH	Important patterns, architectural rules	Surfaced by post-edit-context
MEDIUM	Best practices	Only shown in massu_context
LOW	Nice-to-have suggestions	Only shown in massu_context

Writing Effective Rules

Be Specific

yaml

# Bad - too vague
rules:
  - "Write good code"

# Good - specific and actionable
rules:
  - "All mutations must use protectedProcedure, not publicProcedure"
  - "Database queries must use parameterized values, never string concatenation"

Include the Why

yaml

rules:
  - "Use protectedProcedure for mutations (prevents unauthenticated data modification)"
  - "Never import Node.js modules in middleware (Edge Runtime limitation)"

Group by File Pattern

yaml

rules:
  - pattern: "src/server/routers/**/*.ts"
    severity: CRITICAL
    rules:
      - "All mutations must use protectedProcedure"
      - "Validate all inputs with Zod schemas"

  - pattern: "src/components/**/*.tsx"
    severity: HIGH
    rules:
      - "Use React.memo for list item components"
      - "No direct API calls - use tRPC hooks"

  - pattern: "src/hooks/**/*.ts"
    severity: MEDIUM
    rules:
      - "Custom hooks must be prefixed with 'use'"
      - "Return cleanup functions from useEffect"

  - pattern: "src/middleware.ts"
    severity: CRITICAL
    rules:
      - "No Node.js dependencies (Edge Runtime only)"
      - "No database calls (use Edge-compatible auth)"

Pattern File References

For complex rules with examples and details, reference a pattern file:

yaml

rules:
  - pattern: "src/server/**/*.ts"
    severity: CRITICAL
    patternFile: "patterns/server-rules.md"
    rules:
      - "See .claude/patterns/server-rules.md for complete server coding rules"

The pattern file can include code examples, anti-patterns, and detailed explanations.

How Rules Are Used

post-edit-context hook: Surfaces CRITICAL and HIGH rules when a matching file is edited
massu_context tool: Shows all rules for any file when explicitly requested
massu_validation_check tool: Validates file content against rules (where possible)
Audit trail: Records which rules were in effect when changes were made

Tips

Start with a small set of CRITICAL rules and expand over time
Rules that prevent security issues should always be CRITICAL
Test your glob patterns with massu_context to verify they match the right files
Use patternFile for rules that need examples and detailed explanation
Keep rule descriptions under 100 characters for readability in hook output