revfactory Story Point Estimator
A skill that enhances the effort estimation capabilities of sprint-planner and story-writer.
Target Agents
- sprint-planner — Plans sprint capacity and story allocation
- story-writer — Evaluates complexity when writing user stories
Fibonacci Scale Reference
| SP | Complexity | Uncertainty | Effort | Example |
|---|---|---|---|---|
| 1 | Very Low | None | A few hours | Text change, config value update |
| 2 | Low | Very Low | Half a day | Simple UI component addition |
| 3 | Moderate | Low | 1 day | Single CRUD API, simple screen |
| 5 | Medium | Moderate | 2-3 days | Complex business logic, external API integration |
| 8 | High | High | 1 week | New feature module, authentication system |
| 13 | Very High | Very High | 1-2 weeks | Architecture change, large-scale refactoring |
| 21+ | Needs Decomposition | - | - | Story is too large — decomposition required |
Complexity Assessment Dimensions
Three-Dimensional Assessment Model
Final SP = max(Technical Complexity, Domain Complexity, Uncertainty)
1. Technical Complexity
- Scope of code changes (number of files, number of layers)
- Technical difficulty (algorithms, concurrency, security)
- Testing difficulty (edge cases, integration tests)
2. Domain Complexity
- Number of business rules
- Exception handling scenarios
- Whether stakeholder approval is required
3. Uncertainty
- Whether a technical spike is needed
- External dependencies (APIs, libraries, infrastructure)
- Clarity of requirements
Velocity Calculation
Velocity = Total SP completed in a sprint
Stable velocity calculation:
- Average of the last 3-5 sprints
- Average after removing outliers (extreme values)
- Or use the median
Example:
Sprint 1: 32 SP
Sprint 2: 28 SP
Sprint 3: 35 SP
Sprint 4: 15 SP (outlier due to vacations, etc.)
Sprint 5: 30 SP
Average (outliers removed): (32+28+35+30)/4 = 31.25 SP
Sprint Capacity Calculation
Sprint Capacity = Velocity x Availability Rate
Availability rate calculation:
Total person-days = Team size x Sprint days
Unavailable = Vacations + Training + Meetings + On-call
Available person-days = Total person-days - Unavailable
Availability rate = Available person-days / Total person-days
Example:
5 team members x 10 days = 50 person-days
3 vacation days + 5 meeting days = 8 days
Available: 42 days → Availability rate 84%
Capacity = 31 SP x 0.84 ≈ 26 SP
Buffer:
Stable team: Plan 80% of capacity (20% buffer)
New team/uncertain: Plan 70% of capacity (30% buffer)
User Story Decomposition Criteria
Decomposition is mandatory for stories of 13 SP or more:
Decomposition strategies:
1. By workflow stage
"User makes a payment" →
- Select payment method
- Enter payment information
- Process payment
- Confirm payment
2. By data variation
"Support multiple formats" →
- JSON support
- CSV support
- XML support
3. By user type
"User logs in" →
- Email login
- Social login
- SSO login
4. By CRUD operation
"Product management" →
- List products
- Create product
- Update product
- Delete product
5. By Happy/Sad path
- Normal flow
- Error handling
- Edge cases
Estimation Bias Prevention
1. Anchoring effect prevention
→ Simultaneous reveal (planning poker style)
→ Highest/lowest estimators explain their rationale
2. Optimism bias prevention
→ Consider "worst case" scenarios
→ Include time for testing/review/deployment
3. Parkinson's Law prevention
→ SP measures complexity, not time
→ "3 SP" not "2 days"
4. Reference point alignment
→ Maintain team-wide reference stories
→ Anchors like "Login API = 3 SP"
Deliverable Template
## Story Point Estimation Results
### Velocity: [N] SP/sprint
### Available Capacity: [N] SP (including [M]% buffer)
### Estimation Results
| Story | Technical | Domain | Uncertainty | SP | Notes |
|-------|-----------|--------|-------------|-----|-------|
### Sprint Allocation
| Sprint | Total SP | Story List |
|--------|----------|------------|
| Sprint 1 | 26/31 | [list] |
| Sprint 2 | 28/31 | [list] |