Estimate Stories Skill

Purpose

Estimate story points for user stories using a structured, evidence-based formula: Story Points = (Complexity × Effort) + Risk

This provides consistent estimations that help with sprint planning, velocity tracking, and story comparison.

Core Principle: Estimation is not guessing—it's structured analysis of complexity, effort, and risk based on acceptance criteria and technical context.

Prerequisites

• Story file exists in .claude/stories/ directory
• Story has clear acceptance criteria
• Understanding of project tech stack
• Access to historical velocity data (optional)

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Workflow

1. Load Story Context

Read story file to understand:

• User story narrative (As a... I want... So that...)
• Acceptance criteria (what needs to be implemented)
• Dependencies and technical notes
• Current priority level

Load project context:

• Team velocity baseline (from .claude/config.yaml)
• Tech stack and known patterns
• Historical estimation data (if available)

Example story:

**User Story:** As a new user, I want to create an account with email/password

**Acceptance Criteria:**
- AC-1: User can enter email and password on signup form
- AC-2: Email validated with Zod
- AC-3: Password hashed with bcrypt
- AC-4: Duplicate emails rejected with 409
- AC-5: Success returns JWT token
- AC-6: User record saved to PostgreSQL

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2. Analyze Complexity (1-5 Scale)

Complexity measures technical difficulty and cognitive load (NOT time/effort).

Quick Guide:

• 1 (Trivial): Single file, copy-paste from existing, no edge cases
• 2 (Simple): 2-3 files, existing patterns, minimal edge cases
• 3 (Moderate): 4-6 files, may need new library, multiple edge cases
• 4 (Complex): 7-12 files, multiple patterns, many error paths
• 5 (Very Complex): 12+ files, new architecture, extensive edge cases

Consider:

• Number of integration points (APIs, databases, services)
• Error handling paths required
• State management complexity
• Data transformation complexity

For example story:

Complexity: 3 (Moderate)
- 6 files affected (form, validation, controller, service, model, tests)
- Multiple integration points (DB, JWT, bcrypt)
- Several error paths (validation, duplicates, DB errors)
- Moderate state management

See: references/complexity-scale.md for detailed scale with examples

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3. Analyze Effort (1-5 Scale)

Effort measures the volume of work regardless of difficulty.

Quick Guide:

• 1 (Minimal): <1 hour, <50 LOC, 2-3 tests
• 2 (Small): 1-2 hours, 50-150 LOC, 4-6 tests
• 3 (Medium): 3-4 hours, 150-300 LOC, 7-10 tests
• 4 (Large): 5-6 hours, 300-500 LOC, 11-15 tests
• 5 (Very Large): >6 hours, >500 LOC, 15+ tests

Consider:

• Number of acceptance criteria (more AC = more work)
• Lines of code to write
• Number of tests required
• Documentation needs

For example story:

Effort: 3 (Medium)
- 6 acceptance criteria
- ~250 LOC (controller, service, validation, model)
- ~10 tests (unit + integration)
- 3-4 hours estimated work

See: references/effort-scale.md for detailed scale with examples

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4. Analyze Risk (0-3 Adjustment)

Risk is an adjustment factor for unknowns and potential issues.

Quick Guide:

• 0: No significant risks
• +1: Minor risks (unfamiliar library, some unknowns)
• +2: Moderate risks (new pattern, integration uncertainty)
• +3: High risks (new architecture, external dependencies, R&D needed)

Consider:

• Team familiarity with required tech
• External dependencies (third-party APIs)
• Requirements clarity (vague requirements = higher risk)
• Performance/security concerns

For example story:

Risk: +1
- Team familiar with all tech (Zod, bcrypt, JWT, PostgreSQL)
- Requirements clear and testable
- Minor risk: ensuring proper bcrypt cost and JWT security

See: references/risk-factors.md for detailed risk analysis

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5. Calculate Story Points

Formula: Story Points = (Complexity × Effort) + Risk

For example story:

Complexity: 3
Effort: 3
Risk: +1

Story Points = (3 × 3) + 1 = 10 points

Story Point Scale Interpretation:

• 1-2 points: Trivial, can complete in < 1 hour
• 3-5 points: Small, can complete in 1-3 hours
• 6-10 points: Medium, can complete in half day
• 11-15 points: Large, can complete in 1 day
• 16-20 points: Very large, consider splitting
• 21+ points: Too large, MUST split into smaller stories

If story > 13 points: Consider splitting into smaller stories.

See: references/calculation-guide.md for examples and edge cases

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6. Provide Estimation Rationale

Document WHY this estimate:

## Estimation Rationale

**Story Points:** 10

**Complexity (3/5):** Moderate
- 6 files to modify/create
- Multiple integration points (validation, hashing, DB, JWT)
- Multiple error paths to handle

**Effort (3/5):** Medium
- 6 acceptance criteria
- ~250 lines of code
- ~10 tests required
- Estimated 3-4 hours

**Risk (+1/3):** Minor
- Team familiar with tech stack
- Requirements clear and testable
- Minor security considerations for bcrypt/JWT

**Confidence:** High (80%)
- Clear requirements
- Standard patterns
- No unknowns

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7. Update Story File

Add estimation block to story file:

## Estimation

**Story Points:** 10
**Estimated By:** Alex (Planner)
**Date:** 2025-01-15
**Confidence:** High (80%)

**Breakdown:**
- Complexity: 3/5 (Moderate - 6 files, multiple integrations)
- Effort: 3/5 (Medium - 6 AC, ~250 LOC, ~10 tests, 3-4 hours)
- Risk: +1/3 (Minor - familiar tech, clear requirements)

**Formula:** (3 × 3) + 1 = 10 points

**Assumptions:**
- Team familiar with Zod, bcrypt, JWT, PostgreSQL
- Clear acceptance criteria remain stable
- No major architectural changes needed

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8. Generate Estimation Report (Optional)

For formal estimation reviews or audits, generate comprehensive report:

# Story Estimation Report

## Executive Summary
- **Story:** User Signup with Email/Password
- **Story Points:** 10
- **Confidence:** High (80%)
- **Recommendation:** Ready for sprint planning

## Detailed Analysis
[Complexity, Effort, Risk breakdown]

## Comparable Stories
- story-auth-002-login: 8 points (similar complexity, slightly less effort)
- story-auth-003-password-reset: 13 points (more complex flow)

## Assumptions & Risks
[List key assumptions]

## Sprint Planning Notes
- Can be completed in 1 sprint (assuming 2-week sprint)
- No blocking dependencies
- Suitable for mid-level developer

See: references/report-templates.md for full report format

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Batch Estimation

For multiple stories:

1. Load all stories
2. Estimate each using same process
3. Compare estimates for consistency
4. Adjust if similar stories have very different estimates
5. Generate summary report

Tips for consistency:

• Use same reference points
• Compare with recently estimated similar stories
• Document rationale for each estimate
• Flag outliers for review

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Calibration and Adjustment

After sprint completes:

1. Compare estimated vs actual story points
2. Identify patterns in over/under-estimation
3. Adjust future estimates based on learnings
4. Update complexity/effort/risk scales if needed

Example:

Story estimated: 10 points
Actual velocity: 13 points (30% under-estimated)

Reason: Underestimated integration complexity

Learning: Increase complexity score for multi-API integrations

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Common Scenarios

Story Seems Too Large (>13 points)

Approach:

1. Identify if complexity, effort, or both are high
2. Look for natural split points in acceptance criteria
3. Split into multiple smaller stories
4. Re-estimate each smaller story

Example:

Original: User Profile (21 points)
Split into:
- User Profile - Basic Info (8 points)
- User Profile - Avatar Upload (8 points)
- User Profile - Preferences (5 points)

Uncertainty in Estimation

If confidence < 60%:

1. Identify sources of uncertainty
2. Add risk adjustment
3. Consider spike story for research
4. Document assumptions clearly

Team Disagreement on Estimate

Approach:

1. Each person explains their reasoning
2. Identify where views differ (complexity/effort/risk)
3. Discuss until consensus or average estimates
4. Document the final rationale

See: references/estimation-scenarios.md for complex cases

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Best Practices

1. Be consistent - Use same criteria for all stories
2. Compare similar stories - Check recent similar estimates
3. Document rationale - Explain WHY, not just WHAT
4. Calibrate regularly - Adjust based on actual velocity
5. Split large stories - > 13 points should be split
6. Include the team - Discuss estimates with implementers
7. Track confidence - Low confidence = higher risk adjustment

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Reference Files

• references/complexity-scale.md - Detailed 1-5 complexity scale with examples
• references/effort-scale.md - Detailed 1-5 effort scale with examples
• references/risk-factors.md - Risk analysis framework (0-3)
• references/calculation-guide.md - Formula examples and edge cases
• references/report-templates.md - Comprehensive report formats
• references/estimation-scenarios.md - Complex scenarios and solutions

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When to Escalate

• Story is very large (>20 points) and can't be split
• High uncertainty even after analysis (confidence < 40%)
• Team has no experience with required technology
• Requires significant architectural changes
• Story depends on many external factors

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Part of BMAD Enhanced Planning Suite