Agent Skills: Writing Rules

Writing Rules

Overview

Writing rules IS creating scoped, auto-injected conventions.

Rules auto-inject into context when files match their paths: glob. Keep them concise—every line costs tokens.

Core principle: Rules = conventions for specific files. Laws = immutable constraints for ALL responses. Don't confuse them.

Violating the letter of the rules is violating the spirit of the rules.

Task Initialization (MANDATORY)

Before ANY action, create task list using TaskCreate:

TaskCreate for EACH task below:
- Subject: "[writing-rules] Task N: <action>"
- ActiveForm: "<doing action>"

Tasks:

1. Analyze requirements
2. RED - Test without rule
3. GREEN - Write rule file
4. Validate structure
5. REFACTOR - Quality review
6. Test activation

Announce: "Created 6 tasks. Starting execution..."

Execution rules:

1. TaskUpdate status="in_progress" BEFORE starting each task
2. TaskUpdate status="completed" ONLY after verification passes
3. If task fails → stay in_progress, diagnose, retry
4. NEVER skip to next task until current is completed
5. At end, TaskList to confirm all completed

TDD Mapping for Rules

| TDD Phase | Rule Creation | What You Do | |-----------|---------------|-------------| | RED | Test without rule | Work on matching files, note inconsistencies | | Verify RED | Document gaps | Note where conventions were forgotten | | GREEN | Write rule | Create .claude/rules/ file addressing gaps | | Verify GREEN | Test injection | Verify rule activates on matching files | | REFACTOR | Optimize scope | Tighten paths: globs, reduce line count |

Task 1: Analyze Requirements

Goal: Understand what convention to encode and where it applies.

Questions to answer:

• What convention needs enforcement?
• Which files should this apply to?
• Is this a LAW (immutable) or RULE (convention)?
• Does this rule already exist?

Decision:

Is it IMMUTABLE (must display every response)?
├─ Yes → Use <law> in CLAUDE.md, NOT a rule
└─ No → Is it scoped to specific files?
    ├─ Yes → Use paths: glob
    └─ No → Global rule (no paths:)

Verification: Can state the convention in one sentence and specify the glob pattern.

Task 2: RED - Test Without Rule

Goal: Work on matching files WITHOUT the rule. Note where convention is forgotten.

Process:

1. Identify 2-3 files that would match the rule
2. Ask agent to modify those files
3. Observe if conventions are followed naturally
4. Document specific violations

Verification: Documented at least 1 instance where convention was not followed.

Task 3: GREEN - Write Rule File

Goal: Create rule file addressing the gaps you documented.

Rule Location

.claude/rules/
├── code-style.md         # Global rule (no paths:)
├── api/
│   └── conventions.md    # paths: src/api/**
└── testing/
    └── guidelines.md     # paths: **/*.test.ts

Rule Format

---
paths: src/api/**/*.ts    # Omit for global rules
---

# Rule Title

- Constraint 1 (imperative: "MUST", "NEVER")
- Constraint 2

Writing Rules

CRITICAL constraints:

• < 50 lines - Auto-injected = expensive tokens
• Imperative form - "MUST use", not "try to use"
• No procedures - How-to belongs in skills
• Specific globs - Narrow scope = fewer injections

API Conventions

• MUST validate all input with zod
• MUST return { data, error } shape
• NEVER expose internal errors to client

Specific, imperative, scoped.
</Good>

<Bad>
```yaml
---
# No paths = global!
---

# Guidelines

- Try to validate input
- Consider using consistent response shapes
- It's good practice to handle errors

Vague, unscoped, passive. </Bad>

Verification:

• [ ] Has frontmatter with paths: (or intentionally global)
• [ ] < 50 lines
• [ ] Imperative language ("MUST", "NEVER")
• [ ] Not duplicating existing rules

Task 4: Validate Structure

Goal: Verify rule file structure is correct.

Checklist:

• [ ] File is in .claude/rules/ directory
• [ ] Frontmatter has valid paths: glob (or none for global)
• [ ] Body < 50 lines
• [ ] Uses imperative language
• [ ] No how-to instructions (belongs in skills)
• [ ] Not duplicating a <law> in CLAUDE.md

Verification: All checklist items pass.

Task 5: REFACTOR - Quality Review

Goal: Have rule reviewed by rule-reviewer subagent.

Task tool:
- subagent_type: "rcc:rule-reviewer"
- prompt: "Review rule at [path]"

Outcomes:

• Pass → Proceed to Task 6
• Needs Fix → Fix issues, re-run reviewer, repeat until Pass
• Fail → Major problems, return to Task 3

Verification: rule-reviewer returns "Pass" rating.

Task 6: Test Activation

Goal: Verify rule actually activates on matching files.

Process:

1. Create/open a file matching the paths: pattern
2. Ask agent to modify it
3. Verify agent mentions or follows the rule
4. If global rule, verify it appears in all contexts

Verification:

• Rule activates when working on matching files
• Agent follows the conventions in the rule

Glob Pattern Reference

| Pattern | Matches | |---------|---------| | **/*.ts | All TypeScript files | | src/api/** | All under src/api/ | | *.md | Markdown in root only | | {src,lib}/**/*.ts | Multiple directories | | **/*.{ts,tsx} | Multiple extensions | | !**/node_modules/** | Exclude pattern |

Red Flags - STOP

These thoughts mean you're rationalizing. STOP and reconsider:

• "This should be a law, but I'll make it a rule"
• "I don't need paths:, it applies everywhere"
• "50 lines is too restrictive"
• "Skip baseline, I know what's needed"
• "Add how-to instructions here"
• "One big rule is better than multiple small ones"

All of these mean: You're about to create a weak rule. Follow the process.

Common Rationalizations

| Excuse | Reality | |--------|---------| | "Laws are overkill" | If it's immutable, it's a law. Period. | | "Global rules are fine" | Global = always injected. Scope it properly. | | "50 lines is arbitrary" | 50 lines × N matches = massive token cost. | | "I can add procedures here" | Rules = what. Skills = how. Keep them separate. | | "One comprehensive rule" | Multiple focused rules > one bloated rule. |

Flowchart: Rule Creation

digraph rule_creation {
    rankdir=TB;

    start [label="Need rule", shape=doublecircle];
    analyze [label="Task 1: Analyze\nrequirements", shape=box];
    is_law [label="Is it\nimmutable?", shape=diamond];
    use_law [label="Use <law>\nin CLAUDE.md", shape=box, style=filled, fillcolor="#ffcccc"];
    baseline [label="Task 2: RED\nTest without rule", shape=box, style=filled, fillcolor="#ffcccc"];
    write [label="Task 3: GREEN\nWrite rule", shape=box, style=filled, fillcolor="#ccffcc"];
    validate [label="Task 4: Validate\nstructure", shape=box];
    review [label="Task 5: REFACTOR\nQuality review", shape=box, style=filled, fillcolor="#ccccff"];
    review_pass [label="Review\npassed?", shape=diamond];
    test [label="Task 6: Test\nactivation", shape=box];
    done [label="Rule complete", shape=doublecircle];

    start -> analyze;
    analyze -> is_law;
    is_law -> use_law [label="yes"];
    is_law -> baseline [label="no"];
    baseline -> write;
    write -> validate;
    validate -> review;
    review -> review_pass;
    review_pass -> test [label="pass"];
    review_pass -> write [label="fail"];
    test -> done;
}

References

• references/paths-patterns.md - Advanced glob patterns
• references/examples.md - Rule examples by domain