Benchmark Expert

Benchmark Expert — Performance Baseline & Regression Detection

🔒 Prerequisites (Mandatory)

This skill operates WITHIN the SDD framework. Before starting any benchmark: 0. Mode Check: Verify .hub-mode and apply token-distiller guidelines.

1. Context Check: Rehydrate state by reading STATE.md, MEMORY.md, and LEARNINGS.md.
2. Spec Check: Does the spec.md file exist with clear requirements and Acceptance Criteria (ACs)? (BDD mandatory for Medium+).
3. Plan Check: Does the plan.md file define the architecture and schemas, and include Mermaid diagrams?
4. Contract Check: Was the contract.md file established with validation sensors?
5. Task Check: Is the task list in tasks.md detailed and atomized?
6. Phase 4 Integration: Benchmarks should preferably be executed in Phase 4 (Review & Persistence) of the SDD to validate the implementation impact.
7. Clean Environment: Ensure the test environment is isolated and without heavy background processes.

Goal

The goal of this skill is to provide a standardized framework for performance measurement, allowing developers to establish reliable baselines, detect regressions early, and compare technical alternatives based on quantitative data.

Output Structure

The execution of this skill produces the following artifacts:

When to Use

• Before and after a PR to measure the performance impact.
• Setting up initial baselines for new projects.
• When users report that the system "is slow."
• Before an official release to ensure targets have been met.
• Comparing different libraries or stacks (e.g., Vite vs. Webpack).

Operating Modes

Mode 1: Page Performance (Browser)

Measures real browser metrics via automation tools.

Workflow:

1. Navigate to target URLs.
2. Measure Core Web Vitals:
   • LCP (Largest Contentful Paint): Target < 2.5s.
   • CLS (Cumulative Layout Shift): Target < 0.1.
   • INP (Interaction to Next Paint): Target < 200ms.
   • FCP (First Contentful Paint): Target < 1.8s.
   • TTFB (Time to First Byte): Target < 800ms.
3. Measure resource sizes:
   • Total page weight (Target < 1MB).
   • JS Bundle (Target < 200KB gzipped).
   • CSS, Images, and third-party scripts.

Mode 2: API Performance

Benchmarks API endpoints for latency and robustness.

Workflow:

1. Run 100+ requests on the target endpoint.
2. Measure percentiles: p50, p95, p99.
3. Monitor status codes and response sizes.
4. Test under concurrent load (e.g., 10-50 simultaneous connections).

Mode 3: Build & Dev Loop Performance

Measures the agility of the development ecosystem.

Metrics:

1. Cold Build: Build time from scratch.
2. Hot Reload (HMR): Time between saving a file and reflecting in the UI.
3. Test Duration: Total time for the test suite.
4. Tooling Latency: Time for Lint and Type Check.

Mode 4: Before/After Comparison (Regression)

The heart of the skill for PR validation.

# Save current state as baseline
/benchmark-expert baseline

# ... apply code changes ...

# Compare current state against saved baseline
/benchmark-expert compare

Quality Rules

• Deterministic Measurements: Always run the benchmark 3 times and use the average.
• Context Awareness: Document the specifications of the machine where the benchmark was run.
• Fail Fast: If a critical metric (LCP) delta increases by > 15%, the verdict must be a mandatory FAIL.
• Git Persistence: Critical baselines must be committed to the .benchmarks/ directory.

Prohibited

• NEVER ignore performance regressions in PRs without documented technical justification.
• NEVER run benchmarks on machines with high CPU/Memory load (instability).
• NEVER use benchmark tools that do not measure p99 for APIs.

References

• Performance Targets
• Regression Analysis

version: "2.3.0"
feature_id: "HUB-ALIGNMENT"
phase: "VERIFY"
status: "COMPLETED"
last_update: "2026-05-06T13:16:19.358445Z"
evidence_checksum: "8e52f6a"