writing-plans

name	writing-plans
description	Use when you have a spec or requirements for a multi-step task, before touching code

Writing Plans

Overview

Write comprehensive implementation plans assuming the engineer has zero context for our 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 our toolset or problem domain. Assume they don't know good test design very well.

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

Context: This should be run in a dedicated worktree (created by brainstorming skill).

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.
• You reason best about code you can hold in context at once, and your edits are more reliable when files are focused. Prefer smaller, focused files over large ones that do too much.
• 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.

Understand Before Planning

Before writing the plan, understand the problem domain:

Research Checklist (5-10 minutes)

• Read project documentation - Check plan/TODO.md, plan/CHANGELOG.md, or project AGENTS.md for context
• Review existing implementations - Search for similar features to avoid reinventing the wheel
• Search for utilities/helpers - Look for existing validation, error handling, formatting functions before planning new ones
• Understand constraints - Identify technical boundaries, performance requirements, compatibility needs
• Trace data paths - Understand how data flows through the system
• Clarify ambiguities - Ask your human partner about unclear requirements NOW, not during implementation

Why this matters: Planning without context = writing tasks that duplicate code, violate constraints, or solve the wrong problem.

Example:

❌ BAD: Jump straight to planning
Task 1: Create email validation function
  - Write validateEmail(email: string): boolean
  - Add regex pattern for email format

# Codebase already has EmailValidator class in src/utils/validators/!

✅ GOOD: After 5-min research, found existing validator
Task 1: Extend EmailValidator for new requirement
  - Modify: src/utils/validators/EmailValidator.ts
  - Add domain whitelist checking to existing validator
  - Reuse existing email format validation

Red flags requiring immediate clarification:

• Multiple ways to achieve goal with different trade-offs
• Unclear requirements or success criteria
• Missing information about existing systems
• Contradictory constraints

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

Every plan MUST start with this header:

# [Feature Name] Implementation Plan

> **REQUIRED SUB-SKILL:** Use executing-plans or subagent-driven-development to implement this plan task-by-task.
> **CRITICAL:** Work MUST be done on a feature branch, NEVER on main/master.
> Use using-git-worktrees to create isolated workspace with new branch.

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

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

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

**Git Workflow:**
- Feature branch: `feature/<feature-name>` (created by worktree)
- Push after EACH commit: `git push origin <branch-name>`
- Merge to main/master ONLY after ALL tests pass

---

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

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

git add tests/path/test.py src/path/file.py
git commit -m "feat: add specific feature"
# REQUIRED: Push to remote after EACH commit
git push origin <feature-branch>

## 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

## Remember
- Exact file paths always
- Complete code in every step — if a step changes code, show the code
- Exact commands with expected output
- Reference relevant skills with @ syntax
- DRY, YAGNI, TDD, frequent commits

## 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.

## Execution Handoff

After saving the plan, offer execution choice:

**"Plan complete and saved to `docs/plans/<filename>.md`. Two execution options:**

**1. Subagent-Driven (recommended)** - I dispatch a fresh subagent per task, review between tasks, fast iteration

**2. Inline Execution** - Execute tasks in this session using executing-plans, batch execution with checkpoints

**Which approach?"**

**If Subagent-Driven chosen:**
- **REQUIRED SUB-SKILL:** Use subagent-driven-development
- Fresh subagent per task + two-stage review

**If Inline Execution chosen:**
- **REQUIRED SUB-SKILL:** Use executing-plans
- Batch execution with checkpoints for review