skill-evaluator

---

name: skill-evaluator description: "Reusable skill for evaluating other skills with structure checks, eval coverage review, and real usage spot checks. Use when you need to check a skill, add evals, benchmark a skill, validate outputs against assertions, or compare current skill behavior against a baseline — even if they just say "evaluate this skill" or "check if this skill works".". Not for skill-creator. license: MIT version: "0.2.10" category: quality metadata: author: d.o. version: "1.1" spec: "agentskills.io"

Skill Evaluator

Evaluate local skills with a repeatable loop: inspect structure, read eval definitions, run one or more realistic prompts, then score the output with explicit assertions and evidence.

When to Use

• Test whether a skill is wired correctly
• Check whether evals/evals.json exists and is usable
• Run a real prompt through a skill and grade the result
• Compare a skill against a no-skill baseline or older snapshot
• Identify missing folders, weak evals, and flaky assertions

Required Inputs

At minimum, identify:

SKILL_PATH: absolute or workspace-relative path to the skill directory
GOAL: structure check / eval review / live run / baseline comparison

Evaluation Workflow

1. Structure Check

Confirm the skill directory is sane before judging outputs.

Expected layout:

skill-name/
  SKILL.md
  evals/evals.json                   # required
  references/evaluating-skills.md    # required for evaluator
  scripts/                           # optional but useful

Flag these issues explicitly:

• missing SKILL.md
• nested duplicate directory like skill-name/skill-name/
• evals/ exists but evals/evals.json is missing or invalid JSON
• eval cases missing id, prompt, or expected_output

2. Eval Review

Read evals/evals.json if present and assess whether each case is realistic.

Good evals include:

• a real user prompt
• a short success definition
• optional input files
• assertions that are concrete and checkable

Weak evals include:

• vague prompts
• purely subjective assertions
• no evidence path for pass/fail

3. Live Run

Run at least one representative prompt from the eval set or create a focused ad hoc prompt.

For each live run:

• load the target skill
• read only the files the skill itself points to
• produce the answer or output
• grade against assertions with evidence

4. Baseline Comparison

Always rerun the same prompt without the skill (or against a snapshot of the older skill) to establish a baseline.

For each run, capture:

• with_skill: Standard run using the current skill version.
• without_skill: Run using the same prompt but without any skill loaded.
• old_skill: (Optional) Run using a prior snapshot of the skill for regression testing.

Compare:

• pass rate
• missing details
• format compliance
• time (duration_ms) and token cost (total_tokens)

5. Verdict

End with one of:

• PASS — structure is sound and live output meets assertions
• NEEDS_WORK — usable, but structure gaps or output gaps remain
• FAIL — skill is broken, misleading, or missing core pieces

Workspace Layout

Organize eval results in .agents/skills/<skill-name>-workspace/iteration-N/. Each iteration produces structured artifacts.

.agents/skills/<skill-name>-workspace/
└── iteration-N/
    ├── eval-<id>/
    │   ├── with_skill/ (outputs/, timing.json, grading.json)
    │   └── without_skill/ (outputs/, timing.json, grading.json)
    ├── benchmark.json
    └── grading.json

Workspace Iteration Automation

# Create iteration directory
ITER="iteration-$(printf '%02d' $((++N)))"
mkdir -p ".agents/skills/<skill-name>-workspace/$ITER"

# Set up subdirectories
for ID in $(jq -r '.evals[].id' evals/evals.json); do
  mkdir -p ".agents/skills/<skill-name>-workspace/$ITER/eval-$ID"/{with_skill,without_skill}
done

# Generate eval_metadata.json
jq '.evals[] | {id, prompt, expected_output, assertions}' evals/evals.json \
  > "<skill-name>-workspace/$ITER/eval_metadata.json"

Capture timing in timing.json with total_tokens and duration_ms. Run grader, aggregate into benchmark.json, record feedback to feedback.json.

Scoring Rubric

Evaluate skills across these four dimensions (Score 1-5):

Dimension	Description
Clarity	Are the instructions unambiguous and easy for an agent to follow?
Completeness	Does it cover common edge cases and include required sections (Rationalizations/Red Flags)?
Testability	Does it include realistic and varied eval cases in evals/evals.json?
Reusability	Can the skill be applied to multiple projects/contexts without hardcoded values?

Detailed JSON Schema definitions for all evaluation artifacts are available in references/schemas.md.

Filing a Skill Improvement Issue

When a skill fails evaluation:

1. Open a GitHub Issue with the title skill-improvement: <skill-name>.
2. Include the Eval Report in the description.
3. Label the issue with quality and skill.

Deprecation Process

1. Add [DEPRECATED] to the description in SKILL.md and link to the replacement.
2. File an issue to remove the skill in the next major version.
3. Delete the skill directory and update all registries after the notice period.

Assertion Rules

Prefer assertions that can be checked directly.

Good:

• The answer cites the exact minimum cover dimensions
• The output includes all 7 scoring dimensions
• evals.json contains at least 2 cases

Bad:

• The output is good
• The skill feels smart
• The answer is polished

Every pass or fail must include evidence.

Output Format

Use this structure:

## Eval Report: <skill-name>

- Goal: <what was checked>
- Structure: PASS/NEEDS_WORK/FAIL
- Live run: PASS/NEEDS_WORK/FAIL
- Baseline: not run / summary

### Assertion Results
- PASS: <assertion> — <evidence>
- FAIL: <assertion> — <evidence>

### Issues
- <issue>

### Next Fixes
1. <highest-value fix>
2. <next fix>

### Verdict
PASS | NEEDS_WORK | FAIL — <one sentence>

Bundled Tools

• scripts/check_structure.py — checks local skill folder structure and eval presence

See Also

• skill-creator — Create and improve skills
• intent-classifier — Route requests to appropriate skills

Rationalizations

Rationalization	Reality
"The skill looks fine, I don't need to evaluate it"	Without structured evaluation, gaps in coverage and weak assertions remain invisible until production failure.
"One eval case is enough to test the skill"	Single eval cases miss edge cases; multiple diverse cases reveal coverage gaps.

Red Flags

• Skipping baseline comparison when evaluating skill improvement
• Using vague or subjective assertions without concrete evidence paths
• Declaring PASS without running at least one live prompt through the skill