Breaks work into ordered tasks. Use when you have a spec or clear requirements and need to break work into implementable tasks. Use when a task feels too large to start, when you need to estimate scope, or when parallel work is possible.
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SKILL.md
planning-and-task-breakdown.SKILL.md
---name: planning-and-task-breakdown
description: Breaks work into ordered tasks. Use when you have a spec or clear requirements and need to break work into implementable tasks. Use when a task feels too large to start, when you need to estimate scope, or when parallel work is possible.
---# Planning and Task Breakdown
## Overview
Decompose work into small, verifiable tasks with explicit acceptance criteria. Good task breakdown is the difference between an agent that completes work reliably and one that produces a tangled mess. Every task should be small enough to implement, test, and verify in a single focused session.
## When to Use
- You have a spec and need to break it into implementable units
- A task feels too large or vague to start
- Work needs to be parallelized across multiple agents or sessions
- You need to communicate scope to a human
- The implementation order isn't obvious
**When NOT to use:** Single-file changes with obvious scope, or when the spec already contains well-defined tasks.
## The Planning Process
### Step 1: Enter Plan Mode
Before writing any code, operate in read-only mode:
- Read the spec and relevant codebase sections
- Identify existing patterns and conventions
- Map dependencies between components
- Note risks and unknowns
**Do NOT write code during planning.** The output is a plan document saved to `tasks/plan.md` and a task list saved to `tasks/todo.md`, not implementation.
### Step 2: Identify the Dependency Graph
Map what depends on what:
```
Database schema
│
├── API models/types
│ │
│ ├── API endpoints
│ │ │
│ │ └── Frontend API client
│ │ │
│ │ └── UI components
│ │
│ └── Validation logic
│
└── Seed data / migrations
```
Implementation order follows the dependency graph bottom-up: build foundations first.
### Step 3: Slice Vertically
Instead of building all the database, then all the API, then all the UI — build one complete feature path at a time:
**Bad (horizontal slicing):**
```
Task 1: Build entire database schema
Task 2: Build all API endpoints
Task 3: Build all UI components
Task 4: Connect everything
```
**Good (vertical slicing):**
```
Task 1: User can create an account (schema + API + UI for registration)
Task 2: User can log in (auth schema + API + UI for login)
Task 3: User can create a task (task schema + API + UI for creation)
Task 4: User can view task list (query + API + UI for list view)
```
Each vertical slice delivers working, testable functionality.
### Step 4: Write Tasks
Each task follows this structure:
```markdown
## Task [N]: [Short descriptive title]
**Description:** One paragraph explaining what this task accomplishes.
**Acceptance criteria:**
- [ ] [Specific, testable condition]
- [ ] [Specific, testable condition]
**Verification:**
- [ ] Tests pass: `npm test -- --grep "feature-name"`
- [ ] Build succeeds: `npm run build`
- [ ] Manual check: [description of what to verify]
**Dependencies:** [Task numbers this depends on, or "None"]
1. Dependencies are satisfied (build foundation first)
2. Each task leaves the system in a working state
3. Verification checkpoints occur after every 2-3 tasks
4. High-risk tasks are early (fail fast)
Add explicit checkpoints:
```markdown
## Checkpoint: After Tasks 1-3
- [ ] All tests pass
- [ ] Application builds without errors
- [ ] Core user flow works end-to-end
- [ ] Review with human before proceeding
```
## Task Sizing Guidelines
| Size | Files | Scope | Example |
|------|-------|-------|---------|
| **XS** | 1 | Single function or config change | Add a validation rule |
| **S** | 1-2 | One component or endpoint | Add a new API endpoint |
| **M** | 3-5 | One feature slice | User registration flow |
| **L** | 5-8 | Multi-component feature | Search with filtering and pagination |
| **XL** | 8+ | **Too large — break it down further** | — |
If a task is L or larger, it should be broken into smaller tasks. An agent performs best on S and M tasks.
**When to break a task down further:**
- It would take more than one focused session (roughly 2+ hours of agent work)
- You cannot describe the acceptance criteria in 3 or fewer bullet points
- It touches two or more independent subsystems (e.g., auth and billing)
- You find yourself writing "and" in the task title (a sign it is two tasks)
## Output Files
- **Plan document:** Save the implementation plan to `tasks/plan.md`.
- **Task list:** Save the checklist-style task list to `tasks/todo.md`.
Create the `tasks/` directory if it does not exist. These paths are the convention expected by the `/build` command and other downstream tooling.
## Plan Document Template
```markdown
# Implementation Plan: [Feature/Project Name]
## Overview
[One paragraph summary of what we're building]
## Architecture Decisions
- [Key decision 1 and rationale]
- [Key decision 2 and rationale]
## Task List
### Phase 1: Foundation
- [ ] Task 1: ...
- [ ] Task 2: ...
### Checkpoint: Foundation
- [ ] Tests pass, builds clean
### Phase 2: Core Features
- [ ] Task 3: ...
- [ ] Task 4: ...
### Checkpoint: Core Features
- [ ] End-to-end flow works
### Phase 3: Polish
- [ ] Task 5: ...
- [ ] Task 6: ...
### Checkpoint: Complete
- [ ] All acceptance criteria met
- [ ] Ready for review
## Risks and Mitigations
| Risk | Impact | Mitigation |
|------|--------|------------|
| [Risk] | [High/Med/Low] | [Strategy] |
## Open Questions
- [Question needing human input]
```
## Parallelization Opportunities
When multiple agents or sessions are available:
- **Safe to parallelize:** Independent feature slices, tests for already-implemented features, documentation
- **Must be sequential:** Database migrations, shared state changes, dependency chains
- **Needs coordination:** Features that share an API contract (define the contract first, then parallelize)
## Common Rationalizations
| Rationalization | Reality |
|---|---|
| "I'll figure it out as I go" | That's how you end up with a tangled mess and rework. 10 minutes of planning saves hours. |
| "The tasks are obvious" | Write them down anyway. Explicit tasks surface hidden dependencies and forgotten edge cases. |
| "Planning is overhead" | Planning is the task. Implementation without a plan is just typing. |
| "I can hold it all in my head" | Context windows are finite. Written plans survive session boundaries and compaction. |
## Red Flags
- Starting implementation without a written task list
- Tasks that say "implement the feature" without acceptance criteria
- No verification steps in the plan
- All tasks are XL-sized
- No checkpoints between tasks
- Dependency order isn't considered
## Verification
Before starting implementation, confirm:
- [ ] Every task has acceptance criteria
- [ ] Every task has a verification step
- [ ] Task dependencies are identified and ordered correctly
- [ ] No task touches more than ~5 files
- [ ] Checkpoints exist between major phases
- [ ] The human has reviewed and approved the plan
## See Also
Acceptance criteria are per-task and answer "did we build the right thing?". They sit on top of the project-wide Definition of Done, the standing bar every task clears before it counts as done. See `references/definition-of-done.md`.
