Transform overwhelming development tasks into manageable units by respecting cognitive limits, creating clear boundaries, and enabling parallel work. Tasks properly decomposed achieve 3x higher completion rates and 60% fewer defects.
When to Use This Skill
Use this skill when:
- A task feels too big to estimate
- Unsure where to start
- Blocked by dependencies
- Task keeps growing (scope creep)
- Need to break down an epic or feature
Do NOT use this skill when:
- Task is already small and clear
- Doing implementation work
- Architecture decisions needed (use system-design)
Core Principle
The goal isn't more tasks—it's the right tasks. Tasks small enough to understand completely, large enough to deliver value, independent enough to avoid blocking.
Quick Reference: Cognitive Limits
| Limit | Threshold | Implication |
|---|---|---|
| Working memory | 7±2 items | Max concepts per task |
| Context switch recovery | 23 minutes | Minimize task switching |
| Files examined | 15-20 max | Bound task scope |
| Days before completion drops | 2-3 days | Keep tasks under this |
Task Duration Success Rates
| Duration | Completion Rate |
|---|---|
| < 2 hours | 95% |
| 2-4 hours | 90% |
| 4-8 hours (1 day) | 80% |
| 2-3 days | 60% |
| 1 week | 35% |
| > 2 weeks | <10% |
Diagnostic States
TD1: Too Big to Understand
Symptoms: Estimates range wildly, can't hold all requirements in mind, more than 7 concepts to track
Interventions:
- Apply INVEST criteria: Independent, Negotiable, Valuable, Estimable, Small, Testable
- Use vertical slicing (each slice is independently deployable)
- Apply walking skeleton (minimal end-to-end first)
TD2: No Clear Entry Point
Symptoms: Multiple valid starting points, paralysis, everything seems connected
Interventions:
- Front-load risk: start with highest-uncertainty items
- Tracer bullet: minimal proof of concept
- Find the walking skeleton: thinnest slice through all layers
TD3: Dependency Problems
Symptoms: "Blocked on X", diamond dependencies, coordination overhead
Interventions:
- Interface contracts: define API, mock while implementing
- Feature flags: deploy independently, enable when ready
- Branch by abstraction: create layer, swap implementations
TD4: No Clear Done Criteria
Symptoms: "Almost done" forever, no way to verify completion
Interventions:
- Define acceptance criteria (Given/When/Then)
- Time-box to force prioritization
- Define explicit out-of-scope items
TD5: Scope Creep
Symptoms: Task keeps growing, "while we're here" additions
Interventions:
- Freeze scope, spawn new tasks for additions
- Define minimum viable version
- Ship smallest version that solves the problem
TD6: Need Spike First
Symptoms: Estimate variance > 4x, new technology, multiple approaches
Interventions:
- Time-boxed spike (8 hours max)
- Deliverables: options, POC, trade-offs, revised estimate
- Spike then implement pattern
Decomposition Patterns
Vertical Slicing (Preferred for Features)
Feature: User Profile Management
Slice 1: View basic profile (4h)
- UI: Profile display
- API: GET /profile
- DB: Read profile
Slice 2: Edit profile name (6h)
- UI: Edit dialog
- API: PATCH /profile/name
- DB: Update profile
Each slice is independently deployable
Walking Skeleton (For New Systems)
Minimal end-to-end first:
1. Hello World page
2. One GET endpoint
3. Single table
4. Basic deploy
Then flesh out incrementally
Tracer Bullet (Validate Architecture)
Step 1: Minimal Service A (1h) - Hardcoded response
Step 2: Minimal Service B (1h) - Simple transformation
Step 3: Integrate (2h) - Prove they communicate
Total: 4 hours to decision point
Estimation Techniques
Complexity Sizing (Fibonacci)
| Points | Meaning |
|---|---|
| 1 | Trivial, < 1 hour |
| 2 | Simple, 1-2 hours |
| 3 | Standard, 2-4 hours |
| 5 | Moderate, 4-8 hours |
| 8 | Complex, 1-2 days |
| 13 | Very complex, 2-3 days |
| 21 | Too large, must decompose |
Three-Point Estimation
O = Optimistic (everything perfect)
L = Likely (normal case)
P = Pessimistic (major issues)
PERT estimate: (O + 4L + P) / 6
Anti-Patterns
Big Bang Delivery
Building complete system before any delivery. Fix: Vertical slices, incremental value.
Technical Tasks Without Value
"Set up database," "Create service layer." Fix: Include in feature tasks: "User can view products (includes DB)."
Research Forever
Unbounded investigation. Fix: Time-boxed spikes with deliverables.
Perfect Decomposition
Over-analyzing before starting. Fix: Decompose next 2 weeks. Details for later work emerge.
Decomposition Checklist
Before starting any task:
- Can hold all requirements in working memory?
- Duration under 2-3 days?
- Clear acceptance criteria exist?
- Dependencies identified and broken where possible?
- Can be completed independently?
- Delivers verifiable value?
- Estimate confidence is high?
If any "no" → further decomposition needed.
Related Skills
- github-agile - Track decomposed work as issues
- system-design - Understand architectural boundaries
- requirements-analysis - Clarify unclear requirements
- code-review - Review after implementation