planning-and-task-breakdown

SKILL.md

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:

## 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"]

**Files likely touched:**
- `src/path/to/file.ts`
- `tests/path/to/test.ts`

**Estimated scope:** [Small: 1-2 files | Medium: 3-5 files | Large: 5+ files]

Step 5: Order and Checkpoint

Arrange tasks so that:

Dependencies are satisfied (build foundation first)

Each task leaves the system in a working state

Verification checkpoints occur after every 2-3 tasks

High-risk tasks are early (fail fast)

Add explicit checkpoints:

## 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

# 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.