skill-creator — independently scanned and version-tracked by SaferSkills.
SaferSkills independently audited skill-creator (Agent Skill) and scored it 100/100 (green). The audit ran 55 deterministic rules across Security, Supply Chain, Maintenance, Transparency, and Community; it found 0 high-severity and 0 lower-severity findings. The full rule-by-rule trace and per-finding evidence are below. Free, methodology-open.
Findings & checks · 0 flagged
Every scanned point with the score it earned and what moved between them.
First recorded scan — no prior version to compare against.
The primary manifest — the file an agent reads to learn what this artifact does.
Default operating mode: autonomous — create or update the skill, run evals, improve it, optimize the description, and return with a final report. Only pause for human review if the user explicitly requests it or you hit an ambiguity that can't be resolved from the evidence alone.
At a high level, the process of creating a skill goes like this:
eval-viewer/generate_review.py script to show the results if the user wants to reviewFigure out where the user is in this process and then jump in and help them progress through these stages. Route based on what they need. Of course, you should always be flexible and if the user is like "I don't need to run a bunch of evaluations, just vibe with me", you can do that instead.
Workspace convention: All eval artifacts go in tmp/<skill-name>-workspace/ under the project root (the directory containing .claude/). This directory is gitignored. Within the workspace, organize by iteration (iteration-1/, iteration-2/, etc.).
Nested invocation: When invoked as a subagent with an explicit outputs directory, use that outputs/ directory as the root for all inner workspaces — not tmp/<skill-name>-workspace/.
Track your progress with tasks/todos — without them, description optimization and the judge step are commonly skipped.
The skill creator is liable to be used by people across a wide range of familiarity with coding jargon. If you haven't heard (and how could you, it's only very recently that it started), there's a trend now where the power of Claude is inspiring plumbers to open up their terminals, parents and grandparents to google "how to install npm". On the other hand, the bulk of users are probably fairly computer-literate.
So please pay attention to context cues to understand how to phrase your communication! In the default case, just to give you some idea:
It's OK to briefly explain terms if you're in doubt, and feel free to clarify terms with a short definition if you're unsure if the user will get it.
Start by understanding the user's intent. The current conversation might already contain a workflow the user wants to capture (e.g., they say "turn this into a skill"). If so, extract answers from the conversation history first — the tools used, the sequence of steps, corrections the user made, input/output formats observed. Skip if in autonomous mode: The user may need to fill the gaps, and should confirm before proceeding to the next step.
Skip if in autonomous mode: If a gap is genuinely irresolvable from context and would materially change the skill's correctness, pause and ask. Otherwise infer, state it, and proceed.
Proactively ask questions about edge cases, input/output formats, example files, success criteria, and dependencies. Wait to write test prompts until you've got this part ironed out. SKIP this interview in autonomous mode, let make decisions yourself
Research existing skills — MUST read references/available-skill-resources.md for curated skill repositories, then fetch the README or index of relevant repos to check whether skills for this domain already exist. Don't deep-dive into repos with nothing relevant — a quick scan of the index is enough to know if there's something worth borrowing.
Check available MCPs - if useful for research (searching docs, finding similar skills, looking up best practices), research in parallel via subagents if available, otherwise inline. Come prepared with context to reduce burden on the user.
Based on the user interview, fill in these components:
#### Anatomy of a Skill
skill-name/
├── SKILL.md (required)
│ ├── YAML frontmatter (name, description required)
│ └── Markdown instructions
└── Bundled Resources (optional)
├── scripts/ - Executable code for deterministic/repetitive tasks
├── references/ - Docs loaded into context as needed
└── assets/ - Files used in output (templates, icons, fonts)#### Progressive Disclosure
Skills use a three-level loading system:
These word counts are approximate and you can feel free to go longer if needed.
Key patterns:
Domain organization: When a skill supports multiple domains/frameworks, organize by variant:
cloud-deploy/
├── SKILL.md (workflow + selection)
└── references/
├── aws.md
├── gcp.md
└── azure.mdClaude reads only the relevant reference file.
#### Principle of Lack of Surprise
This goes without saying, but skills must not contain malware, exploit code, or any content that could compromise system security. A skill's contents should not surprise the user in their intent if described. Don't go along with requests to create misleading skills or skills designed to facilitate unauthorized access, data exfiltration, or other malicious activities. Things like a "roleplay as an XYZ" are OK though.
#### Writing Patterns
Prefer using the imperative form in instructions.
Defining output formats - You can do it like this:
## Report structure
ALWAYS use this exact template:
# [Title]
## Executive summary
## Key findings
## RecommendationsExamples pattern - It's useful to include examples. You can format them like this (but if "Input" and "Output" are in the examples you might want to deviate a little):
## Commit message format
**Example 1:**
Input: Added user authentication with JWT tokens
Output: feat(auth): implement JWT-based authenticationTry to explain to the model why things are important in lieu of heavy-handed musty MUSTs. Use theory of mind and try to make the skill general and not super-narrow to specific examples. Start by writing a draft and then look at it with fresh eyes and improve it.
After writing the skill draft, come up with 2-3 realistic test prompts — the kind of thing a real user would actually say. Share them with the user if they want to review: "Here are a few test cases I'd like to try. Do these look right, or do you want to add more?" In autonomous mode, proceed directly.
Save test cases to <workspace>/evals.json. Don't write expectations yet — just the prompts. You'll draft expectations in Step 2 while the runs are in progress.
{
"skill_name": "example-skill",
"evals": [
{
"id": 1,
"prompt": "User's task prompt",
"expected_output": "Description of expected result",
"files": []
}
]
}See references/schemas.md for the full schema (including the expectations field).
Good test cases are realistic (messy, specific — what a real user would type), substantive (complex enough that the skill makes a difference), diverse (different use cases, not three variations of the same prompt), and discriminating (test skill-specific behaviors, not generic task completion — ask "would bare Claude pass this?" and if yes, make it harder).
Also prepare 20 trigger eval queries for description optimization and save to <workspace>/trigger-eval.json. See the Description Optimization section below for the format. Doing this now means description optimization can launch immediately.
This section is one continuous sequence — don't stop partway through. Do NOT use /skill-test or any other testing skill.
Within the workspace, organize results by iteration (iteration-1/, iteration-2/, etc.) and within that, each test case gets a descriptive directory name (e.g., handle-multi-page-pdf/). Don't create all of this upfront — just create directories as you go.
Description optimization only depends on the frontmatter description and trigger eval queries — it's independent of the skill body. Run it in parallel with the eval loop:
cd <skill-creator-dir> && python -m scripts.run_loop \
--eval-set <workspace>/trigger-eval.json \
--skill-path <path-to-skill> \
--model <model-id-powering-this-session> \
--max-iterations 5 --report none --verbose \
--output <workspace>/run-loop-results.json \
> <workspace>/run-loop.log 2>&1 &
echo "run_loop PID: $!"Save the PID — you'll need it later to check completion. Continue immediately to Step 1.
Every eval must use a real subagent that actually executes the task. Reading a skill and imagining it would work is not evaluation — it's guesswork. Spawn all test cases in parallel, each as a separate subagent:
Execute this task with the following skill loaded.
Read the skill at [skill SKILL.md path] first — it contains your instructions.
Task: [eval prompt]
Input files: [eval files if any, or "none"]
Save outputs to: [workspace path]/iteration-[N]/[eval-name]/with_skill/outputs/
Outputs to save: [what the user cares about — e.g., "the .docx file", "the final CSV"]
Also required: write `outputs/transcript.md` — one line per tool call, in order, as you go: `- <Tool> | <key args> | <ok|error>`. Graders use this to verify process assertions. No transcript = failed process assertions.
Do NOT revert or clean up the project after completing the task. The orchestrator handles cleanup after grading.Project cleanup timing: Executors must not revert changes — doing so destroys evidence before graders can inspect it (new files, diffs, task artifacts). The orchestrator is responsible for restoring the project state after all graders have finished. This sequence matters: grade first, clean second.
Baseline runs (new skills only) — When creating a new skill, the first iteration MUST include baseline runs alongside with-skill runs. Run the same prompts without the skill loaded and save outputs to without_skill/outputs/. This measures whether the skill actually adds value over bare Claude. For subsequent iterations, baseline from iteration 1 still applies — no need to rerun.
Baseline runs for existing skills — When improving an existing skill, baseline runs are optional. Only run them when the user explicitly requests comparison. Existing skills have already proven their value.
Write an eval_metadata.json for each test case (expectations can be empty for now). Give each eval a descriptive name based on what it's testing — not just "eval-0". Use this name for the directory too. If this iteration uses new or modified eval prompts, create these files for each new eval directory — don't assume they carry over from previous iterations.
{
"eval_id": 0,
"eval_name": "descriptive-name-here",
"prompt": "The user's task prompt",
"expectations": []
}Don't just wait for the runs to finish — you can use this time productively. Draft quantitative expectations for each test case. Good expectations are objectively verifiable and have descriptive names — they should read clearly in the benchmark viewer so someone glancing at the results immediately understands what each one checks. Subjective skills (writing style, design quality) are better evaluated qualitatively — don't force expectations onto things that need human judgment.
Write expectations that test what the skill specifically teaches, not just structural presence. Before writing each one, ask: "Would bare Claude likely get this right without the skill?" If yes, the expectation isn't discriminating — make it harder. Target project-specific conventions, ordering/sequencing the skill introduces, and exact implementation details (column names, error codes, ID formats) rather than topic mentions.
Update the eval_metadata.json files and evals.json with the expectations once drafted.
When each subagent task completes, you receive a notification containing total_tokens and duration_ms. Save this data immediately to timing.json in the run directory:
{
"total_tokens": 84852,
"duration_ms": 23332,
"total_duration_seconds": 23.3
}This is the only opportunity to capture this data — it comes through the task notification and isn't persisted elsewhere. Process each notification as it arrives rather than trying to batch them.
Once all runs are done:
agents/grader.md and evaluates expectations against the outputs. When spawning, pass these inputs explicitly: Read agents/grader.md at <skill-creator-path>/agents/grader.md — it contains your role.
transcript_path: <run>/outputs/transcript.md
outputs_dir: <run>/outputs/
expectations: [...]Save results to grading.json in each run directory. The grading.json expectations array must use the fields text, passed, and evidence — the viewer depends on these exact field names. For expectations that can be checked programmatically, write and run a script rather than eyeballing it.
python -m scripts.aggregate_benchmark <workspace>/iteration-N --skill-name <name>This produces benchmark.json and benchmark.md with pass_rate, time, and tokens for each configuration. If generating benchmark.json manually, see references/schemas.md for the exact schema.
agents/analyzer.md for what to look for — non-discriminating expectations, high-variance evals, time/token tradeoffs, and repeated failure modes that should become skill instructions or bundled scripts.model: "opus" — judgment calls benefit from the most capable model: Read agents/judge.md at <skill-creator-path>/agents/judge.md — it contains your role and output format.
Then evaluate:
- Previous benchmark: `<workspace>/iteration-<N-1>/benchmark.md` (skip for iteration 1)
- Current benchmark: `<workspace>/iteration-<N>/benchmark.md`
- Remaining failures: [paste analyst notes]
- Skill diff: [paste the diff of what changed, or "Initial version" for iteration 1]Save the full output to <workspace>/iteration-<N>/judge-output.json.
Trust the judge's decision. If it says stop, stop. Don't override.
Stop thresholds (all must be met):
nohup python <skill-creator-path>/eval-viewer/generate_review.py \
<workspace>/iteration-N \
--skill-name "my-skill" \
--benchmark <workspace>/iteration-N/benchmark.json \
> /dev/null 2>&1 &
VIEWER_PID=$!For iteration 2+, also pass --previous-workspace <workspace>/iteration-<N-1>.
If staying autonomous, write down iteration takeaways: what failed, why, and whether the skill is beating the baseline.
After aggregating benchmark data for the first iteration of a new skill, check whether the assertions are actually discriminating:
When the gate fails:
eval_feedback for flagged weak assertionsDo NOT mix assertion revisions with skill improvements across iterations — changing what you measure while changing what you're testing makes it impossible to track whether the skill actually improved.
This gate does not apply to existing skill improvements (no baseline data to compare against).
When the user tells you they're done, read feedback.json. Empty feedback means the user thought it was fine. Focus your improvements on the test cases where the user had specific complaints. Kill the viewer when done (kill $VIEWER_PID 2>/dev/null).
This is the heart of the loop. You've run the test cases, you have benchmark data, and now you need to make the skill better.
create_docx.py or a build_chart.py, that's a strong signal the skill should bundle that script. Write it once, put it in scripts/, and tell the skill to use it. This saves every future invocation from reinventing the wheel.This task is pretty important and your thinking time is not the blocker; take your time and really mull things over. I'd suggest writing a draft revision and then looking at it anew and making improvements. Really do your best to get into the head of the user and understand what they want and need.
After improving the skill:
<workspace>/iteration-<N+1>/skill_changes.json documenting what changed: ["Added error handling section", "Removed redundant examples", "Bundled helper script"]Each entry should be a human-readable string. For iteration 1, write ["Initial version"].
iteration-<N+1>/ (with-skill only — baseline from iteration 1 still applies)--previous-workspace pointing at the previous iterationSafety limit: pause at 3 iterations. The judge should stop this at 1-2 naturally. Reaching 3 without meeting thresholds means something structural is wrong — stop and diagnose whether the problem is the skill or the test cases. If the root cause is bad test cases, rewrite evals rather than continuing.
Keep going until:
For situations where you want a more rigorous comparison between two versions of a skill (e.g., the user asks "is the new version actually better?"), there's a blind comparison system. Read agents/comparator.md and agents/analyzer.md for the details. The basic idea is: give two outputs to an independent agent without telling it which is which, and let it judge quality. Then analyze why the winner won.
This is optional, requires subagents, and most users won't need it. The human review loop is usually sufficient.
The description field in SKILL.md frontmatter is the primary mechanism that determines whether Claude invokes a skill. If you launched description optimization in Step 0 during the eval loop, check on it now. Otherwise, run it after the skill body is finalized.
Create 20 eval queries — a mix of should-trigger and should-not-trigger. Save as JSON:
[
{"query": "the user prompt", "should_trigger": true},
{"query": "another prompt", "should_trigger": false}
]The queries must be realistic and something a Claude Code or Claude.ai user would actually type. Not abstract requests, but requests that are concrete and specific and have a good amount of detail. For instance, file paths, personal context about the user's job or situation, column names and values, company names, URLs. A little bit of backstory. Some might be in lowercase or contain abbreviations or typos or casual speech. Use a mix of different lengths, and focus on edge cases rather than making them clear-cut (the user will get a chance to sign off on them).
Bad: "Format this data", "Extract text from PDF", "Create a chart"
Good: "ok so my boss just sent me this xlsx file (its in my downloads, called something like 'Q4 sales final FINAL v2.xlsx') and she wants me to add a column that shows the profit margin as a percentage. The revenue is in column C and costs are in column D i think"
For the should-trigger queries (8-10), think about coverage. You want different phrasings of the same intent — some formal, some casual. Include cases where the user doesn't explicitly name the skill or file type but clearly needs it. Throw in some uncommon use cases and cases where this skill competes with another but should win.
For the should-not-trigger queries (8-10), the most valuable ones are the near-misses — queries that share keywords or concepts with the skill but actually need something different. Think adjacent domains, ambiguous phrasing where a naive keyword match would trigger but shouldn't, and cases where the query touches on something the skill does but in a context where another tool is more appropriate.
The key thing to avoid: don't make should-not-trigger queries obviously irrelevant. "Write a fibonacci function" as a negative test for a PDF skill is too easy — it doesn't test anything. The negative cases should be genuinely tricky.
Present the eval set to the user for review using the HTML template:
assets/eval_review.html__EVAL_DATA_PLACEHOLDER__ → the JSON array of eval items (no quotes around it — it's a JS variable assignment)__SKILL_NAME_PLACEHOLDER__ → the skill's name__SKILL_DESCRIPTION_PLACEHOLDER__ → the skill's current description/tmp/eval_review_<skill-name>.html) and open it: open /tmp/eval_review_<skill-name>.html~/Downloads/eval_set.json — check the Downloads folder for the most recent versionIn autonomous mode, skip this step and proceed directly to the optimization loop.
cd <skill-creator-dir> && python -m scripts.run_loop \
--eval-set <path-to-trigger-eval.json> \
--skill-path <path-to-skill> \
--model <model-id-powering-this-session> \
--max-iterations 5 --report none --verbose \
--output <workspace>/run-loop-results.json \
> <workspace>/run-loop.log 2>&1 &
echo "run_loop PID: $!"Use the model ID from your system prompt (the one powering the current session) so the triggering test matches what the user actually experiences.
This handles the full optimization loop automatically. It splits the eval set into 60% train and 40% held-out test, evaluates the current description (running each query 3 times to get a reliable trigger rate), then calls Claude to propose improvements based on what failed. It re-evaluates each new description on both train and test, iterating up to 5 times.
Understanding the triggering mechanism helps design better eval queries. Skills appear in Claude's available_skills list with their name + description, and Claude decides whether to consult a skill based on that description. The important thing to know is that Claude only consults skills for tasks it can't easily handle on its own — simple, one-step queries like "read this PDF" may not trigger a skill even if the description matches perfectly, because Claude can handle them directly with basic tools. Complex, multi-step, or specialized queries reliably trigger skills when the description matches.
This means your eval queries should be substantive enough that Claude would actually benefit from consulting a skill. Simple queries like "read file X" are poor test cases — they won't trigger skills regardless of description quality.
Take best_description from <workspace>/run-loop-results.json and update the skill's SKILL.md frontmatter. Show the user before/after and report the scores.
If best_description is unchanged from the original (the loop found no improvement), you have two options: (1) accept the original and stop, or (2) manually write a new candidate based on the failing test queries. If you choose (2), rerun the loop with --description-override "<candidate>" before applying — never apply an untested manual description directly to SKILL.md.
Always generate and open a visual HTML report:
python <skill-creator-path>/eval-viewer/generate_report.py \
<workspace> \
--skill-name "<name>" \
--run-loop-results <workspace>/run-loop-results.json \
-o <workspace>/report.htmlThe --run-loop-results flag is optional — include it only if description optimization was run. After generating: open <workspace>/report.html
Include a brief text summary: what you changed and why, key outcomes, description optimization result, any remaining risks.
If the user asked whether a skill is ready to ship, give a direct recommendation: Ship, Ship with caveats, or Not ready — with specific reasons.
Packaging: For a distributable .skill file, run python -m scripts.package_skill <path/to/skill-folder>.
The agents/ directory contains instructions for specialized subagents. Read them when you need to spawn the relevant subagent.
agents/grader.md — How to evaluate expectations against outputsagents/judge.md — Independent agent that decides whether to continue or stop iteratingagents/comparator.md — How to do blind A/B comparison between two outputsagents/analyzer.md — How to analyze why one version beat anotherThe references/ directory has additional documentation:
references/schemas.md — JSON structures for evals.json, grading.json, benchmark.json, etc.references/available-skill-resources.md — Curated skill repositories for researchThe core loop, one more time:
Track these steps with tasks/todos to make sure nothing gets skipped. Good luck!
~30 seconds. Free. No account. Every finding cites a rule and a line of evidence.