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, 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]
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Description:
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One paragraph explaining what this task accomplishes.
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Acceptance criteria:
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[
] [
Specific, testable condition
]
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[
] [
Specific, testable condition
]
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Verification:
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[ ] Tests pass:
npm test -- --grep "feature-name"
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[ ] Build succeeds:
npm run build
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[ ] Manual check: [description of what to verify]
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Dependencies:
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[Task numbers this depends on, or "None"]
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Files likely touched:
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src/path/to/file.ts
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tests/path/to/test.ts
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Estimated scope:
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[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. 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 | |
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| | [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