Fitness Function Design
Design metrics that measure architecture health (coupling, modularity, scalability). Automate fitness function checks in CI/CD. Use when establishing quality gates or measuring architectural degradation.
Install
$ agentstack add skill-sethdford-claude-skills-fitness-function-design ✓ scanned · ✓ verified, works with Claude Code, Cursor, and more.
Security review
✓ PassedNo issues found. Passed automated security review. · v0.1.0 How review works →
- ✓ Prompt-injection patterns
- ✓ Secret / credential exfiltration
- ✓ Dangerous shell & filesystem operations
- ✓ Untrusted network calls
- ✓ Known-malicious package signatures
What it can access
- ✓ Network access No
- ✓ Filesystem access No
- ✓ Shell / process execution No
- ✓ Environment & secrets No
- ✓ Dynamic code execution No
From automated source analysis of v0.1.0. “Used” means the capability is present in the source — more access means more to trust, not that it’s unsafe.
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Passed review? Show it. Paste this badge into your README, it links to the public security report.
Links to your public security report.[](https://agentstack.voostack.com/security/report/skill-sethdford-claude-skills-fitness-function-design) Reliability & compatibility
Declared compatibility
Compatibility is declared by the source manifest. End-to-end runtime verification is coming, see below.
We're building live execution health for every listing: tool-call success rate, median latency, uptime, and last-checked timestamps, measured, not self-reported. It isn't live yet, so we don't show numbers we can't stand behind.
How agent discovery & health will work →About
Fitness Function Design
Design quantifiable metrics to measure architecture health and automatically enforce quality standards.
Context
You are designing fitness functions to measure architectural quality. Create metrics for coupling, modularity, scalability, performance. Automate checks in CI/CD for continuous feedback.
Domain Context
Based on evolutionary architecture and fitness function research (Thoughtworks):
- Coupling Metrics: Layer violations, cyclic dependencies, test isolation
- Modularity Metrics: Module fan-in/fan-out, cohesion, abstract instability
- Scalability Metrics: Throughput (RPS), latency (p95, p99), resource utilization
- Security Metrics: Secrets in code, dependency vulnerabilities, known security patterns
- Code Quality Metrics: Complexity (cyclomatic), duplication, test coverage
Instructions
- Identify Key Quality Attributes: What matters most? Scalability? Security? Testability? Maintainability? Pick 3-4.
- Define Metrics for Each Attribute: Scalability: p99 latency 80% test coverage, no untestable dependencies.
- Set Thresholds: Below threshold: pass. Above: fail (blocks merge). Make thresholds achievable but stretch. Too strict: teams bypass. Too loose: no effect.
- Automate Checks: Integrate into CI/CD. Run on every PR. Parse test coverage reports, dependency scanners, performance benchmarks. Fail PR if fitness functions breach.
- Monitor and Adjust: Track metrics over time. Are they trending right? Do developers understand why they matter? Adjust thresholds based on feedback and organizational priorities.
Anti-Patterns
- Too Many Fitness Functions: 50 metrics in CI/CD. Result: long builds, false positives, ignored. Guard: 5-10 core metrics max. Automate what matters; remove noise.
- Fitness Functions Without Context: "Cyclomatic complexity > 10 fails". Developer doesn't understand why. Result: frustrated, rules bypassed. Guard: Document rationale; train teams; explain tradeoffs.
- Static Thresholds: Set once, never changed. Organization evolves, thresholds stale. Result: metrics become irrelevant. Guard: Review quarterly; adjust based on trends and priorities.
- Metrics Without Action: Fitness functions fail but no one addresses. Result: technical debt accumulates. Guard: Failed checks require action; track and fix root causes.
Further Reading
- Evolutionary Architecture by Rebecca Parsons, Neal Ford, Patrick Kua — fitness function concepts
- Building Microservices by Sam Newman — quality metrics for distributed systems
- Accelerate by Nicole Forsgren — DORA metrics for deployment performance
Source & license
This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.
- Author: sethdford
- Source: sethdford/claude-skills
- License: MIT
Install and usage instructions live in the source repository linked above.
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Versions
- v0.1.0 Imported from the upstream source.