Writing Implementation Plans

Overview

Write comprehensive implementation plans that any developer can execute. Break work into bite-sized tasks (2-5 minutes each). Include exact file paths, complete code, exact commands, and expected output.

Core principle: A plan with placeholders is a plan that hasn't been written.

Save plans to: docs/plans/YYYY-MM-DD-<feature-name>.md

When to Use

Use after the design is approved (via EnterPlanMode). Do NOT use for simple single-file changes, purely conversational exploration, or configuration-only changes.

File Structure

Before defining tasks, map out which files will be created or modified. Design units with clear boundaries and well-defined interfaces. Prefer smaller, focused files.

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

Plan Document Header

# [Feature Name] Implementation Plan

**Goal:** [One sentence describing what this builds]
**Architecture:** [2-3 sentences about approach]
**Tech Stack:** [Key technologies/libraries]

---

Task Structure

### Task N: [Component Name]

**Files:**
- Create: exact/path/to/file.py
- Modify: exact/path/to/existing.py

- [ ] Step 1: Write the failing test
  [complete test code here]

- [ ] Step 2: Run test to verify it fails
  Run: pytest tests/path/test.py -v
  Expected: FAIL

- [ ] Step 3: Write minimal implementation
  [complete implementation code here]

- [ ] Step 4: Run test to verify it passes
  Run: pytest tests/path/test.py -v
  Expected: PASS

- [ ] Step 5: Commit
  git add ... && git commit -m "..."

No Placeholders — The Hard Rule

These are plan failures — never write them:

• "TBD", "TODO", "implement later", "fill in details"
• "Add appropriate error handling" / "add validation" (without actual code)
• "Write tests for the above" (without actual test code)
• "Similar to Task N" (repeat the code — tasks may be read out of order)
• Steps describing what to do without showing how

Self-Review

After writing the plan:

1. Coverage check: Can you point to a task for each requirement?
2. Placeholder scan: Search for "TBD", "TODO", vague instructions
3. Type consistency: Do signatures match across tasks?

Execution

After saving the plan, present it to the user. Track execution with TaskCreate/TaskUpdate. Execute tasks using TDD (test-first). After each task, verify before marking complete.