planner

name	planner
description	Write comprehensive implementation plans from approved designs — task decomposition with exact file paths, code, commands. Includes independence analysis for parallel dispatch and no-placeholder enforcement.

Planner — Task Decomposition Skill

Write detailed, executable implementation plans that sub-agents (coders) can follow without any additional context. Plans assume the engineer has zero familiarity with the codebase.

Always announce at start: "I'm using the planner skill to create the implementation plan."

Prerequisites

• An approved design document from the researcher skill
• Read and understood AGENTS.md if it exists

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, suggest breaking into separate plans. Each plan should produce working, testable software on its own. If the user proceeds with a single plan covering multiple subsystems, structure it so each subsystem has clearly separated task groups.

File Structure Mapping

Before defining tasks, map out which files will be created or modified:

• Design units with clear boundaries and well-defined interfaces
• Each file should have one clear responsibility
• Prefer smaller, focused files over large ones that do too much
• Files that change together should live together — split by responsibility, not technical layer
• Follow established patterns in existing codebases (don't unilaterally restructure)
• This structure informs task decomposition and parallel independence analysis

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

> **For agentic workers:** Use skills/coder to implement each task. Read the full task description — don't summarize or skip steps.

**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

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"

## No Placeholders (Enforced)

Every step must contain the actual content an implementer 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 implementer 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

## Independence Analysis (Critical for Parallel Dispatch)

After defining all tasks, analyze which ones can run in parallel:

**Independent tasks (can dispatch together):**
- Modify completely different files with no shared mutable state
- Different subsystems, different modules
- One modifies `src/auth/` and another modifies `src/api/`
- Doc updates alongside code changes

**Dependent tasks (must be sequential):**
- Task B depends on code that Task A creates
- Both tasks modify the same file
- Integration work that requires a specific component to exist first

Output an analysis at the end of the plan:

```markdown
## Parallel Dispatch Analysis

### Batch 1 (independent — dispatch together):
- Task 1 (src/auth/login.ts) + Task 3 (src/api/routes.ts) + Task 5 (docs/README.md)
  Rationale: No shared files, no cross-dependencies

### Batch 2 (depends on Batch 1):
- Task 4 (tests/integration/auth-api.test.ts)
  Rationale: Requires both auth module and API routes to exist before testing

### Single tasks:
- Task 2 (src/models/user.ts) — standalone, can run whenever

Self-Review

After writing the complete plan, check it yourself:

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

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

3. Type consistency: Do the types, method signatures, and property names used in later tasks match what was 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. If a spec requirement has no task, add the task.

Execution Handoff

After saving the plan:

"Plan complete and saved to docs/plans/<filename>.md. Ready for parallel dispatch via skills/coder."

The plan is now ready for the orchestrating agent to execute — it will dispatch coders in batches per the independence analysis. No further handoff needed from this skill.

Key Principles

• Exact file paths always
• Complete code in every step — if a step changes code, show the code
• Exact commands with expected output
• DRY, YAGNI, TDD, frequent commits
• Independence analysis enables parallel dispatch (saves wall-clock time)