Agent Skills: Eval Creator

Eval Creator

Turns promoted learnings into permanent eval cases. Runs regression checks to verify promoted rules hold. This is the outer loop's regress-test step.

The blog says: "If a failure taught you something important, it should become a permanent test case. Otherwise the knowledge is still fragile."

When to Use

• After harness-updater promotes a pattern — create an eval for it
• On cadence — run all evals to check for regression
• Before major releases — verify the harness is holding
• When a promoted rule seems to have stopped working — diagnose with targeted eval run

Eval Directory Structure

.evals/
  EVAL_INDEX.md          # Index of all eval cases with status
  cases/
    eval-YYYYMMDD-001.md # Individual eval case
    eval-YYYYMMDD-002.md
    ...

Creating an Eval Case

Input

From harness-updater or manually:

• Pattern-Key of the promoted learning
• The rule that was added to CLAUDE.md / AGENTS.md
• What to test (the assertion)
• Verification method

Eval Case Format

---
id: eval-YYYYMMDD-NNN
pattern-key: [from learning]
source: [LRN-YYYYMMDD-001, ERR-YYYYMMDD-003]
promoted-rule: "[the rule text in CLAUDE.md]"
promoted-to: CLAUDE.md
created: YYYY-MM-DD
last-run: YYYY-MM-DD
last-result: pass | fail | skip
---

## What This Tests

[One sentence: what failure this eval prevents from recurring]

## Precondition

[What must be true for this eval to be runnable]
- File X exists
- Project uses framework Y
- etc.

## Verification Method

[One of: grep-check, command-check, file-check, rule-check]

### grep-check
Search for a pattern that should (or should not) exist:

target: src/**/*.ts pattern: "hardcoded-secret-pattern" expect: not_found

### command-check
Run a command and check the exit code or output:

command: npm run typecheck expect_exit: 0

### file-check
Verify a file or section exists:

target: CLAUDE.md section: "## Verification" expect: exists

### rule-check
Verify a rule exists in an instruction file:

target: CLAUDE.md contains: "[the promoted rule text or key phrase]" expect: found

## Expected Result

**Pass:** [What "good" looks like]
**Fail:** [What regression looks like]

## Recovery Action

If this eval fails:
1. [Specific step to diagnose]
2. [Specific step to fix]
3. Re-run this eval to verify

Running Evals

Run All

Read .evals/EVAL_INDEX.md, iterate through all cases, execute each verification method.

Run by Pattern-Key

Filter to evals matching a specific pattern.

Run by Area

Filter to evals whose source files match an area (frontend, backend, etc.).

Execution

For each eval case:

1. Check precondition — if not met, mark as skip
2. Execute verification method:
   • grep-check: Use Grep tool to search target files for the pattern
   • command-check: Run the command via Bash, check exit code and/or output
   • file-check: Use Read/Glob to verify file/section existence
   • rule-check: Read the target file, search for the expected content
   • skill-check: Run quick_validate.py on a skill directory (see Skill Validation below)
   • script-check: Run a custom mcp-script by name (see Custom Verification Methods)
3. Compare result to expected
4. Update last-run and last-result in the eval case file
5. Update EVAL_INDEX.md with the result

Regression Report

## Eval Run: YYYY-MM-DD

**Total:** N evals
**Passed:** N
**Failed:** N
**Skipped:** N

### Failures

#### eval-YYYYMMDD-001 — [pattern-key]
- **What regressed:** [description]
- **Expected:** [X]
- **Got:** [Y]
- **Recovery action:** [from eval case]

### Summary
[All green / N regressions need attention]

Eval Index Format

.evals/EVAL_INDEX.md:

# Eval Index

| ID | Pattern-Key | Rule Summary | Last Run | Result | Created |
|----|-------------|-------------|----------|--------|---------|
| eval-YYYYMMDD-001 | auth-middleware-lock | Run migrations on test DB first | YYYY-MM-DD | pass | YYYY-MM-DD |
| eval-YYYYMMDD-002 | pnpm-not-npm | Use pnpm in this repo | YYYY-MM-DD | fail | YYYY-MM-DD |

Integration

Upstream

• harness-updater flags eval candidates after promoting a pattern
• learning-aggregator identifies patterns with clear pass/fail conditions

Downstream

• Regression failures feed back into self-improvement as new error entries
• Persistent failures may indicate the promoted rule needs refinement → feed back to harness-updater

Scheduled Use

For projects with a CI pipeline, eval-creator can run as a scheduled check:

• Weekly: run all evals
• Per-PR: run evals related to changed files
• Post-promotion: run the newly created eval immediately

Custom Verification Methods (mcp-scripts) — Extension Point

These are examples of what's possible with gh-aw mcp-scripts, not features shipped with this plugin. Projects define their own scripts.

Beyond the four built-in methods (grep-check, command-check, file-check, rule-check), projects can define custom verification tools as mcp-scripts for complex assertions that the built-ins can't express.

Example — an eval that verifies a promoted auth rule is enforced:

# In gh-aw workflow config
mcp-scripts:
  check-auth-middleware:
    lang: javascript
    description: "Verify all /admin routes have auth middleware"
    run: |
      const routes = require('./src/routes/admin');
      const unprotected = routes.filter(r => !r.auth);
      if (unprotected.length) {
        console.error('Unprotected admin routes:', unprotected.map(r => r.path));
        process.exit(1);
      }

Reference the script in an eval case as verification_method: script-check with the mcp-script name. This is an extension point — the built-in methods cover most cases, but mcp-scripts handle project-specific behavioral assertions.

Persistence — Extension Point

repo-memory is a gh-aw feature for durable cross-environment storage. This plugin works without it — .evals/ in the working directory is the default.

By default, eval cases live in .evals/ in the working directory. For teams using repo-memory, eval cases can be stored on a memory branch — making them available across environments and surviving ephemeral workspace teardown.

Skill Validation (skill-check)

The Anthropic /skill-creator skill includes two validation systems that eval-creator can use:

Structural validation via quick_validate.py

The skill-check verification method runs the skill-creator's quick_validate.py script on a skill directory. It checks:

• SKILL.md exists with valid YAML frontmatter
• Only allowed frontmatter keys (name, description, license, allowed-tools, metadata, compatibility)
• Name is kebab-case, max 64 chars, no leading/trailing/consecutive hyphens
• Description has no angle brackets, max 1024 chars
• Compatibility field max 500 chars if present

Eval case example:

---
id: eval-YYYYMMDD-NNN
pattern-key: skill-quality.verify-gate
verification_method: skill-check
target: skills/verify-gate
expect: valid
---

## What This Tests
Verify that the verify-gate skill passes structural validation after harness updates.

Execution: python .claude/skills/skill-creator/scripts/quick_validate.py <target>. Exit 0 = pass, exit 1 = fail.

Behavioral validation via run_eval.py

For deeper validation, the skill-creator's run_eval.py tests whether a skill's description causes Claude to invoke it for given queries. This is useful when harness-updater modifies a skill's description or the outer loop creates a new skill — the eval verifies the skill still triggers correctly.

This requires Claude CLI access and is expensive. Use it for high-value skills only, not as a routine CI check.

When to create skill-check evals

Two scenarios connect the outer loop to skill validation:

1. Harness-updater modifies a skill: When a promoted rule is inserted into a SKILL.md (rather than CLAUDE.md), create a skill-check eval to verify the skill remains structurally valid after the edit.

2. Self-improvement identifies a skill gap: When learning-aggregator classifies a pattern as skill_gap and recommends "create a new skill", the new skill should pass quick_validate.py before being committed. Create a skill-check eval for it that persists as a regression test.

This closes the loop: failure → learning → new/updated skill → eval verifies skill quality → regression prevents quality drift.

What This Skill Does NOT Do

• Does not fix regressions (reports them for the agent or human to fix)
• Does not promote learnings (that's harness-updater)
• Does not analyze patterns (that's learning-aggregator)
• Does not replace project test suites — evals test the harness, not the code