writing-plans

Overview

Create implementation plans for an engineer with zero codebase context.

Each plan includes:

• Exact file paths for every operation
• Complete code (not "add validation here")
• Test-first approach with verification commands
• Bite-sized steps (2-5 min each)

Principles: DRY, YAGNI, TDD, frequent commits.

Announce at start: "I'm using the writing-plans skill to create the implementation plan."

Context: Run in dedicated worktree. If none exists, use using-git-worktrees skill first.

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

Before Writing

1. Read spec/requirements completely
2. Explore project structure (view .)
3. Identify tech stack (package.json, pyproject.toml, etc.)
4. Note existing patterns in similar files
5. Check docs/ for existing conventions

Bite-Sized Task Granularity

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

• "Write the failing test" — step
• "Run it to confirm failure" — step
• "Implement minimal code to pass" — step
• "Run tests to confirm pass" — step
• "Commit" — step

Plan Document Header

Every plan MUST start with this 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:123-145`
- Test: `tests/exact/path/to/test.py`

**Step 1: Write the failing test**

```python
def test_specific_behavior():
    result = function(input)
    assert result == expected
```

**Step 2: Run test to verify it fails**

Run: `pytest tests/path/test.py::test_name -v`
Expected: FAIL with "function not defined"

**Step 3: Write minimal implementation**

```python
def function(input):
    return expected
```

**Step 4: Run test to verify it passes**

Run: `pytest tests/path/test.py::test_name -v`
Expected: PASS

**Step 5: Commit**

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

Before Handoff

Verify plan completeness:

• Every file path exists or will be created
• Every command can be run exactly as written
• No TODO/placeholder text remains
• Tests cover all acceptance criteria from spec
• Include exact test code, not descriptions

Execution Handoff

After saving plan, present:

"Plan saved to docs/plans/<filename>.md. Choose execution mode:

1. Subagent-Driven — same session, fresh subagent per task, fast iteration
2. Parallel Session — new session, batched execution with checkpoints

Which approach?"

If Subagent-Driven chosen

• Stay in this session
• REQUIRED SUB-SKILL: subagent-driven-development
• Fresh subagent per task + two-stage review

If Parallel Session chosen

• Guide user to open new session in worktree
• REQUIRED SUB-SKILL: New session uses executing-plans