Writing Plans

Overview

Write comprehensive implementation plans assuming the engineer has zero context for the codebase and questionable taste. Document everything they need to know: which files to touch for each task, code, testing, docs they might need to check, how to test it. Give them the whole plan as bite-sized tasks. DRY. YAGNI. TDD. Frequent commits.

Assume they are a skilled developer, but know almost nothing about the toolset or problem domain. Assume they don't know good test design very well.

Core principle: Plans must be executable without asking questions.

The Iron Law

NO VAGUE STEPS - EVERY STEP IS A SPECIFIC ACTION

"Add validation" is not a step. "Write test for empty email, run it, implement check, run it, commit" - that's 5 steps.

Bite-Sized Task Granularity

Each step is one action (2-5 minutes):

• "Write the failing test" - step
• "Run it to make sure it fails" - step
• "Implement the minimal code to make the test pass" - step
• "Run the tests and make sure they pass" - step
• "Commit" - step

Not a step:

• "Add authentication" (too vague)
• "Implement the feature" (multiple actions)
• "Test it" (which tests? how?)

Plan Document Header

Every plan MUST start with this header:

# [Feature Name] Implementation Plan

> **For Claude:** REQUIRED: Follow this plan task-by-task using TDD.

**Goal:** [One sentence describing what this builds]

**Architecture:** [2-3 sentences about approach]

**Tech Stack:** [Key technologies/libraries]

**Prerequisites:** [What must exist before starting]

---

Task Structure

### Task N: [Component Name]

**Files:**
- Create: `exact/path/to/file.ts`
- Modify: `exact/path/to/existing.ts:123-145`
- Test: `tests/exact/path/to/test.ts`

**Step 1: Write the failing test**

```typescript
test('specific behavior being tested', () => {
  const result = functionName(input);
  expect(result).toBe(expected);
});

Step 2: Run test to verify it fails

Run: npm test tests/path/test.ts -- --grep "specific behavior" Expected: FAIL with "functionName is not defined"

Step 3: Write minimal implementation

function functionName(input: InputType): OutputType {
  return expected;
}

Step 4: Run test to verify it passes

Run: npm test tests/path/test.ts -- --grep "specific behavior" Expected: PASS

Step 5: Commit

git add tests/path/test.ts src/path/file.ts
git commit -m "feat: add specific feature"

## Requirements Checklist

Before writing a plan:

- [ ] Problem statement clear
- [ ] Users identified
- [ ] Functional requirements listed
- [ ] Non-functional requirements listed (performance, security, scale)
- [ ] Constraints documented
- [ ] Success criteria defined
- [ ] Existing code patterns understood

## Risk Assessment Table

For each identified risk:

| Risk | Probability (1-5) | Impact (1-5) | Score | Mitigation |
|------|-------------------|--------------|-------|------------|
| API timeout | 3 | 4 | 12 | Retry with backoff |
| Invalid input | 4 | 2 | 8 | Validation layer |
| Auth bypass | 2 | 5 | 10 | Security review |

Score = Probability × Impact. Address risks with score > 8 first.

## Risk-Based Testing Matrix

**Match testing depth to task risk:**

| Task Risk | Example | Tests Required |
|-----------|---------|----------------|
| Trivial | Typo fix, docs update | None |
| Low | Single file change, utility function | Unit tests only |
| Medium | Multi-file feature, new component | Unit + Integration tests |
| High | Cross-service, auth, state management | Unit + Integration + E2E tests |
| Critical | Payments, security, data migrations | All tests + Security audit |

**How to assess risk:**
- How many files touched? (1 = low, 3+ = medium, cross-service = high)
- Is it auth/payments/security? (always high or critical)
- Is it user-facing? (medium minimum)
- Can it cause data loss? (high or critical)

**Use this matrix when planning test steps. Don't over-test trivial changes. Don't under-test critical ones.**

## Functionality Flow Mapping

Before planning, document all flows:

**User Flow:**

1. User clicks [button]
2. System shows [form]
3. User enters [data]
4. System validates [input]
5. System saves [data]
6. System shows [confirmation]

**Admin Flow:**

1. Admin opens [dashboard]
2. Admin selects [item]
3. System shows [details]
4. Admin changes [setting]
5. System applies [change]

**System Flow:**

1. Request arrives at [endpoint]
2. Middleware validates [auth]
3. Controller calls [service]
4. Service queries [database]
5. Response returns [data]

## Red Flags - STOP and Revise

If you find yourself:

- Writing "add feature" without exact file paths
- Skipping the test step
- Combining multiple actions into one step
- Using "etc." or "similar" instead of explicit steps
- Planning without understanding existing code patterns
- Creating steps that take more than 5 minutes
- Not including expected output for test commands

**STOP. Revise the plan with more specific steps.**

## Rationalization Prevention

| Excuse | Reality |
|--------|---------|
| "They'll know what I mean" | No they won't. Be explicit. |
| "Too much detail is annoying" | Vague plans cause bugs. |
| "Testing is obvious" | Write the test command. |
| "File paths are discoverable" | Write the exact path. |
| "Commits are implied" | Write when to commit. |
| "They can figure out edge cases" | List every edge case. |

## Output Format

```markdown
# [Feature Name] Implementation Plan

> **For Claude:** REQUIRED: Follow this plan task-by-task using TDD.

**Goal:** [One sentence]

**Architecture:** [2-3 sentences]

**Tech Stack:** [Technologies]

**Prerequisites:** [Requirements]

---

## Phase 1: Foundation

### Task 1: [First Component]

**Files:**
- Create: `src/path/file.ts`
- Test: `tests/path/file.test.ts`

**Step 1:** Write failing test
[code block with test]

**Step 2:** Run test, verify fails
Run: `[command]`
Expected: FAIL

**Step 3:** Implement
[code block with implementation]

**Step 4:** Run test, verify passes
Run: `[command]`
Expected: PASS

**Step 5:** Commit
```bash
git add [files]
git commit -m "feat: [description]"

Task 2: [Second Component]

...

Risks

Success Criteria

• All tests pass
• Feature works as specified
• No regressions
• Code reviewed

## Execution Handoff

After saving the plan, offer execution choice:

**"Plan complete. Two execution options:**

**1. Subagent-Driven (this session)** - Fresh subagent per task, review between tasks, fast iteration

**2. Manual Execution** - Follow plan step by step, verify each step

**Which approach?"**

## Remember

- Exact file paths always
- Complete code in plan (not "add validation")
- Exact commands with expected output
- DRY, YAGNI, TDD, frequent commits
- Each step = one action (2-5 minutes)
- No assumptions about context