/agent-benchmark

name: agent-benchmark
description: Framework for measuring and tracking agent response quality over time. Detects regressions before they reach production. Use when evaluating agent changes, auditing quality, or establishing performance baselines.

Agent Benchmark Framework

Without benchmarks, we cannot know whether agent changes improve or degrade quality. This skill defines how to measure, track, and protect agent performance.

When to Activate

• Before and after modifying any agent definition file
• When adding a new skill that an agent depends on
• Periodic quality audits (weekly/monthly)
• When a user reports degraded agent output
• Before promoting an agent from experimental to production

Core Concepts

Why Benchmarks Matter

Agent quality degrades silently. A prompt tweak that improves one response can break ten others. Without a baseline to compare against, every change is a guess. Benchmarks make quality visible and regressions detectable.

Benchmark Types

| Type | Scope | Cost | Frequency | |------|-------|------|-----------| | Prompt Benchmark | Single agent, single task | Low | Every agent change | | Task Benchmark | End-to-end scenario | Medium | Feature changes | | Regression Suite | All critical agents | High | Weekly / before release |

Directory Structure

~/.claude/benchmarks/
  fixtures/
    code-reviewer/
      missing-error-handling.ts      # Input: code with no try/catch
      sql-injection.py               # Input: unparameterized query
      clean-code.ts                  # Input: code with no issues
    security-reviewer/
      hardcoded-secret.ts            # Input: API key in source
      parameterized-query.py         # Input: safe query (no findings expected)
    verifier/
      passing-build/                 # Input: project that builds
      failing-types/                 # Input: project with type errors
  ground-truth/
    code-reviewer/
      missing-error-handling.json    # Expected findings
      sql-injection.json             # Expected findings
      clean-code.json                # Expected: empty findings
    security-reviewer/
      hardcoded-secret.json
      parameterized-query.json
  rubrics/
    code-reviewer.md                 # Scoring rubric
    security-reviewer.md
    verifier.md
  baselines/
    code-reviewer-2026-03-01.json    # Timestamped baseline scores
    code-reviewer-2026-03-26.json
    security-reviewer-2026-03-26.json
  results/
    run-2026-03-26T14-00.json        # Latest run output

Scoring Rubric Template

Each agent has its own rubric file. The template:

## [Agent Name] Scoring Rubric

### Completeness (0-30 points)
Did the agent find everything it should have found?

- Found all expected issues: 30
- Missed 1 non-critical issue: 22
- Missed 1 critical issue: 10
- Missed 2+ issues: 5
- Found nothing when issues exist: 0

### Accuracy (0-30 points)
Were the findings correct? No false positives?

- All findings verified correct: 30
- 1 false positive: 22
- 2 false positives: 12
- 3+ false positives: 5
- Majority of findings are wrong: 0

### Actionability (0-20 points)
Did the agent give concrete, implementable fixes?

- Clear fix with file/line reference: 20
- Clear fix without location: 14
- Vague suggestion (refactor this): 7
- No fix suggested: 0

### Format Compliance (0-20 points)
Did the output follow the agent's output contract?

- Matches contract exactly (VERDICT + sections): 20
- Minor deviation (missing one section): 12
- Major deviation (no VERDICT): 5
- Unstructured free text: 0

Ground Truth Format

Ground truth files define what a correct agent response must contain:

{
  "fixture": "missing-error-handling.ts",
  "agent": "code-reviewer",
  "required_findings": [
    {
      "id": "missing-try-catch",
      "severity": "HIGH",
      "description_contains": ["error handling", "try", "catch"],
      "location_hint": "fetchUserData"
    }
  ],
  "forbidden_findings": [],
  "required_verdict": "FAIL",
  "min_score": 70
}

Scoring Logic

How a Run Is Scored

1. Load fixture (input code / task)
2. Run agent with fixture as input
3. Parse agent output
4. Check required_findings: each found = +completeness points
5. Check forbidden_findings: each false positive = -accuracy points
6. Check verdict matches required_verdict
7. Check format follows output contract
8. Sum scores → final 0-100
9. Compare against min_score threshold

Score Interpretation

| Score | Status | Action | |-------|--------|--------| | 90-100 | EXCELLENT | No action needed | | 75-89 | GOOD | Minor tuning optional | | 60-74 | WARN | Investigate degradation | | 40-59 | POOR | Agent needs rework | | 0-39 | CRITICAL | Block deployment |

Running Benchmarks

Run All Benchmarks

# Full suite
node ~/.claude/benchmarks/run.mjs

# Output: results/run-{timestamp}.json

Run Single Agent

# Benchmark one agent
node ~/.claude/benchmarks/run.mjs --agent code-reviewer

# With verbose output (shows actual vs expected per fixture)
node ~/.claude/benchmarks/run.mjs --agent code-reviewer --verbose

Compare Against Baseline

# Compare latest run against saved baseline
node ~/.claude/benchmarks/run.mjs --compare

# Compare specific run against specific baseline
node ~/.claude/benchmarks/run.mjs \
  --compare results/run-2026-03-26.json \
  --baseline baselines/code-reviewer-2026-03-01.json

Update Baseline

Only run this after verifying an improvement is real:

# Promote latest results to new baseline
node ~/.claude/benchmarks/run.mjs --baseline update

# Creates: baselines/{agent}-{date}.json

Regression Detection Rules

A regression is triggered when:

1. **Score drops more than 10 points** on any single fixture 2. **Average score drops more than 5 points** across all fixtures for an agent 3. **A previously PASS fixture becomes FAIL** 4. **Format compliance drops below 80** (agent stopped following output