writing-plans

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

Writing Plans

Purpose: Decompose a spec or requirement into bite-sized, status-readable tasks with explicit proofs. Consumer: Implementer (subagent or human) who will execute the plan task-by-task. Failure consequence: Vague plan leads to wasted execution; missing proofs mean no completion signal; missing status fields make the plan un-reviewable. Falsifier: Fewer than 3 tasks, single-step work, or trivial change where decomposition adds overhead.

Redteam forwarder: Before dispatching implementers, run /redteam:plan (architect lane) on the plan file. Catches missing proofs, vague success criteria, and dependency conflicts that surface only when an implementer hits them.

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: If working in an isolated worktree, it should have been created via using-git-worktrees at execution time.

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 has one clear responsibility.
• Prefer smaller, focused files over large files 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, do not unilaterally restructure; if a file you modify 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.

Task Right-Sizing

A task is the smallest unit that carries its own test cycle and is worth a fresh reviewer's gate. When drawing task boundaries: fold setup, configuration, scaffolding, and documentation steps into the task whose deliverable needs them; split only where a reviewer could meaningfully reject one task while approving its neighbor. Each task ends with an independently testable deliverable.

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.

Status Contract

Every plan in docs/plans/ must be status-readable without interpreting prose. Use a small metadata block after the worker note. Values are deliberately plain text so markdownlint, grep, and simple scripts can validate them.

Allowed Status: values:

• planned
• active
• blocked
• implemented
• superseded

Required metadata keys:

• Status:
• Owner:
• Last verified:
• Source:
• Canonical issue/ADR/spec:

Use none when no canonical issue, ADR, or spec exists. Use not verified only before any verification has run; update it with YYYY-MM-DD once evidence exists.

Plan Document Header

Every plan MUST start with this header:

# [Feature Name] Implementation Plan

> **For agentic workers:** REQUIRED SUB-SKILL: Use `subagent-driven-development` for subagent execution or `executing-plans` for inline execution. Steps use checkbox (`- [ ]`) syntax for tracking.

Status: planned
Owner: agent | human | mixed
Last verified: not verified
Source: spec path, prompt, `.sf` record, or manual
Canonical issue/ADR/spec: path-or-none

## Goal

[One sentence describing what this builds.]

## PDD Contract

- Purpose:
- Consumer:
- Contract:
- Failure boundary:
- Evidence:
- Falsifier:
- Non-goals:
- Invariants:
- Assumptions:

## Architecture

[2-3 sentences about approach.]

## Tech Stack

[Key technologies/libraries.]

## Done When

- [ ] Observable acceptance criterion with command, trace, commit, or file path.
- [ ] Another acceptance criterion.

## Global Constraints

[The spec's project-wide requirements — version floors, dependency limits,
naming and copy rules, platform requirements — one line each, with exact
values copied verbatim from the spec. Every task's requirements implicitly
include this section.]

---

Task Structure

### Task N: [Component Name]

Status: planned
Proof: not verified
Blocker: none

**Files:**

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

**Interfaces:**

- Consumes: [what this task uses from earlier tasks — exact signatures]
- Produces: [what later tasks rely on — exact function names, parameter
  and return types. A task's implementer sees only their own task; this
  block is how they learn the names and types neighboring tasks use.]

- [ ] **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"
```

When execution updates a task, change Status: and Proof: near that task. Valid task status values are planned, active, blocked, and implemented. Proof: must name the command, trace, commit, PR, or file path that proves the task status. If blocked, Blocker: must name the concrete missing input or failing command.

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 read 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
• Purpose contract, DRY, YAGNI, TDD, frequent commits
• Plan-level Status: plus task-level Status: / Proof: fields.
• Markdown that passes repo markdownlint without local rule disables.

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 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.

4. Status readability: Can rg "^Status:|^Proof:|^- \\[[ xX]\\]" show the plan state? Does every task have Status:, Proof:, and Blocker:?

5. Markdown lint: Run the repo's markdownlint command, or a targeted markdownlint-cli2 <plan-file> when no repo command exists. Fix warnings in the plan instead of disabling rules.

If you find issues, fix them inline. No need to re-review; 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:

Say:

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

1. Subagent-Driven - Use one implementer and review gate per task

2. Inline Execution - Execute tasks in this session 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