writing-plans

name	writing-plans
description	Use when you have a spec or requirements for a multi-step task, before touching code. Produces a bite-sized, TDD-shaped implementation plan with exact files, code, and commands. Output is the plan; hardening and execution are separate steps owned by the caller.
license	MIT

Writing Plans

Overview

Write comprehensive implementation plans for a developer who is technically skilled but has zero context for this codebase, problem domain, and toolset — and assume limited test design judgment. 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. Apply DRY, YAGNI, and TDD; plan for frequent commits.

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

• (User preferences for plan location override this default)

Scope Check

If the spec covers multiple independent subsystems, it should have been broken into sub-project specs during brainstorming. If it wasn't, suggest breaking this into separate plans — one per subsystem. Each plan should produce working, testable software on its own.

File Structure

Before defining tasks, map out which files will be created or modified and what each one is responsible for. This is where decomposition decisions get locked in.

• Design units with clear boundaries and well-defined interfaces. Each file should have one clear responsibility.
• Files that change together should live together. Split by responsibility, not by technical layer.
• In existing codebases, follow established patterns. If the codebase uses large files, don't unilaterally restructure - but if a file you're modifying has grown unwieldy, including a split in the plan is reasonable.

This structure informs the task decomposition. Each task should produce self-contained changes that make sense independently.

Bite-Sized Task Granularity

Each step is one action (2-5 minutes). For code tasks, follow the TDD cycle:

• "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

For tasks with no meaningful unit test (config, dependency, docs, or manual-verification changes), drop the test steps and give a concrete verification step instead — the exact command to run or the exact thing to check, with expected output. Do not fabricate a placeholder test.

Plan Document Header

Every plan starts with this header:

# [Feature Name] Implementation Plan

> **For implementers:** steps use checkbox (`- [ ]`) syntax for tracking — execute them task-by-task. Hardening this plan (with a grill skill: `grill-with-docs` against an existing codebase, or `grill-me` for greenfield) and executing it are separate steps.

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

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

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

---

Task Structure

The examples below use Python/pytest only for illustration — write every code block and command in the plan's actual language and test runner.

### 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"
```

No Placeholders

Every step must contain the actual content an engineer needs. These are plan failures — never write them:

• "TBD", "TODO", "implement later", "fill in details"
• "Add appropriate error handling" / "add validation" / "handle edge cases"
• "Write tests for the above" (without actual test code)
• "Similar to Task N" (repeat the code — the engineer may be reading tasks out of order)
• Steps that describe what to do without showing how (code blocks required for code steps)
• References to types, functions, or methods not defined in any task

Self-Review

After writing the complete plan, look at the spec with fresh eyes and check the plan against it. This is a checklist you run yourself — not a subagent dispatch.

1. Spec coverage: Skim each section/requirement in the spec. Can you point to a task that implements it? List any gaps.

2. Placeholder scan: Search your plan for red flags — any of the patterns from the "No Placeholders" section above. Fix them.

3. Type consistency: Do the types, method signatures, and property names you used in later tasks match what you defined in earlier tasks? A function called clearLayers() in Task 3 but clearFullLayers() in Task 7 is a bug.

If you find issues, fix them inline. No need to re-review — just fix and move on. If you find a spec requirement with no task, add the task.

After the plan

This skill's output is the saved plan file. Two things typically follow, but they are separate steps owned by the caller or workflow — don't auto-invoke them from here:

• Harden it — a fresh plan is ideal grilling material (grill-with-docs against an existing codebase's domain model, or grill-me for greenfield / standalone plans).
• Execute it — work the tasks in order, following each step exactly and running every verification. Never start implementation on main/master without explicit user consent.