N-Version Programming Workflow Skill

Purpose

Execute N-version programming workflow for critical implementations where multiple independent solutions should be generated and compared to select the best approach.

When to Use This Skill

USE FOR:

• Critical security features (authentication, authorization)
• Complex algorithms with multiple valid approaches
• High-risk refactoring of core components
• Architecture decisions with significant long-term impact
• When correctness is paramount over speed

AVOID FOR:

• Simple CRUD operations
• Straightforward bug fixes
• Documentation updates
• Minor UI tweaks
• Time-sensitive quick fixes

Configuration

Core Parameters

N (Number of Versions):

• 3 - Default for standard tasks
• 4-6 - Critical features requiring high confidence
• 2 - Quick validation of approach

Selection Criteria (priority order):

1. Correctness - Meets requirements and passes tests
2. Security - No vulnerabilities or anti-patterns
3. Simplicity - Ruthless simplicity, minimal complexity
4. Philosophy Compliance - Follows project principles
5. Performance - Efficiency and resource usage

Agent Diversity Profiles:

• conservative - Proven patterns and safety
• innovative - Novel approaches and optimizations
• minimalist - Ruthless simplicity
• pragmatic - Balance trade-offs for practical solutions
• performance-focused - Optimize for speed and efficiency

Execution Process

Step 1: Prepare Common Context

• Use prompt-writer agent to create crystal-clear specification
• Document all requirements explicitly
• Define success criteria measurably
• Prepare identical task specification for all N versions
• Identify evaluation metrics upfront
• CRITICAL: Capture explicit user requirements that CANNOT be optimized away

Output: Single authoritative specification document

Step 2: Generate N Independent Implementations

• Spawn N Claude subprocesses simultaneously
• Each subprocess receives IDENTICAL task specification
• NO context sharing between subprocesses (true independence)
• Each uses different agent diversity profile
• Each produces complete implementation with tests
• Each works in isolated directory (version_1/, version_2/, etc.)

Example for N=3:

• Subprocess 1: Conservative approach (proven patterns, comprehensive error handling)
• Subprocess 2: Pragmatic approach (balance simplicity and robustness)
• Subprocess 3: Minimalist approach (ruthless simplification, minimal dependencies)

Step 3: Collect and Compare Implementations

• Wait for all N implementations to complete
• Use analyzer agent to examine each implementation
• Use tester agent to run tests for each version
• Document results in comparison matrix

Comparison Matrix:

| Version | Correctness | Security | Simplicity | Philosophy | Performance | Lines of Code |
|---------|-------------|----------|------------|------------|-------------|---------------|
| v1      | PASS        | PASS     | 7/10       | 8/10       | 150ms       | 180           |
| v2      | PASS        | PASS     | 9/10       | 9/10       | 180ms       | 95            |
| v3      | FAIL        | N/A      | 10/10      | 7/10       | N/A         | 65            |

Step 4: Review and Evaluate

• Use reviewer agent for comprehensive comparison
• Use security agent to evaluate security of each version
• Apply selection criteria in priority order
• Eliminate versions that fail correctness tests
• Compare remaining versions on other criteria
• Identify best parts of each implementation

Evaluation Process:

1. Filter: Remove versions failing correctness tests
2. Security Gate: Eliminate versions with security issues
3. Philosophy Check: Score each on simplicity and compliance
4. Performance Compare: Measure and compare benchmarks
5. Synthesis: Identify if hybrid approach could be superior

Step 5: Select or Synthesize Solution

Decision Tree:

1. Is there ONE version that passes all criteria?
   • YES → Select it and document why
   • NO → Continue to step 2
2. Are there 2+ versions tied on top criteria?
   • YES → Continue to step 3
   • NO → Select highest scoring version
3. Do versions have complementary strengths?
   • YES → Synthesize hybrid combining best parts
   • NO → Select based on weighted criteria priority

Example Synthesis:

Selected: Hybrid of v1 and v2
- Core logic from v2 (ruthless simplicity)
- Error handling from v1 (comprehensive coverage)
- Testing approach from v2 (focused, minimal)
- Documentation style from v1 (thorough)

Rationale: v2's minimalist core paired with v1's robust
error handling provides optimal balance of simplicity
and production-readiness.

Step 6: Implement Selected Solution

• Use builder agent to implement final version
• If single version selected: Use it directly
• If synthesis: Implement hybrid combining best parts
• Preserve all explicit user requirements from Step 1
• Run full test suite
• Document selection rationale in code comments

Documentation Template:

"""
N-Version Implementation Selection

Generated Versions: 3
Selection: Hybrid of v1 (conservative) and v2 (pragmatic)

Rationale:
- v1 had superior error handling and edge case coverage
- v2 had cleaner architecture and better testability
- v3 failed correctness tests (edge case handling)

This implementation combines v2's core logic with v1's
defensive programming approach for production robustness.

Selection Criteria Applied:
1. Correctness: v1=PASS, v2=PASS, v3=FAIL
2. Security: All passed
3. Simplicity: v2 ranked highest
4. Philosophy: v1 and v2 tied
5. Performance: Negligible difference

Step 7: Document Learnings

• Create analysis document: n_version_analysis.md
• Document all N implementations generated
• Explain selection rationale in detail
• Capture insights from rejected versions
• Update .claude/context/DISCOVERIES.md with patterns learned
• Include comparison matrix for future reference

Trade-Offs

Cost: N times the compute resources and time Benefit: Significantly reduced risk of critical errors Best For: Features where bugs are expensive (security, data integrity)

Examples

Example 1: Authentication System

Task: Implement JWT-based authentication Configuration: N=4 (critical security feature) Profiles: conservative, security-focused, pragmatic, minimalist

Result:

• v1 (conservative): Most comprehensive but over-engineered
• v2 (security-focused): Excellent security but complex
• v3 (pragmatic): Good balance, missing edge cases
• v4 (minimalist): Too simple, security gaps

Selection: Hybrid of v2 and v3

• Security implementation from v2
• API design and simplicity from v3

Rationale: Security cannot be compromised, but v3's cleaner API design improved usability without sacrificing security.

Example 2: Data Processing Pipeline

Task: Process large CSV files efficiently Configuration: N=3 (performance-critical) Profiles: pragmatic, performance-focused, minimalist

Result:

• v1 (pragmatic): Pandas-based, familiar but slow
• v2 (performance-focused): Custom streaming, 10x faster
• v3 (minimalist): Python CSV module, simple but slow

Selection: v2 (performance-focused)

Rationale: Performance requirements justified complexity. v2's streaming approach met throughput requirements while v1 and v3 could not scale.

Philosophy Alignment

This workflow enforces:

• Reduced Risk: Multiple implementations catch errors single approach might miss
• Exploration: Different approaches reveal design trade-offs
• Evidence-Based Selection: Systematic comparison vs. gut feeling
• Learning: Rejected versions still provide valuable insights
• Parallel Execution: N implementations run simultaneously for efficiency

Integration with Default Workflow

This workflow replaces Steps 4-5 (Research/Design and Implementation) of the DEFAULT_WORKFLOW when enabled. All other steps (requirements, testing, CI/CD) remain the same.