Writing Skills

Writing Skills

Objective

Produce professional-grade skills: high-signal, safe, portable, and reliably triggerable. This skill:

• Writes or updates a skill directory (SKILL.md + optional scripts/, references/, assets/)
• Generates agents/openai.yaml UI metadata
• Runs validation (skillcheck)
• Runs a critic review using $reviewing-skills and iterates until the bar is met

When to use / When not to use

Use when:

• The user asks to create a new skill (SKILL.md + optional scripts/, references/, assets/).
• The user asks to refactor, tighten, or “upgrade” an existing skill for trigger precision and token efficiency.

Do not use when:

• The user only wants a rubric-based review/grade of an existing skill (use $reviewing-skills).
• The request is not about a skill directory containing SKILL.md.

Quality Bar (default)

Target the rubric's canonical meets_bar. reviewing-skills/references/skills-rubric.md owns it and is authoritative — read it; do not maintain a simplified copy here (a stale local subset is exactly how authors end up targeting the wrong, easier bar — so this file deliberately does not restate the thresholds).

The gate is non-compensatory (one weak dimension fails it regardless of the others). When you author toward it, keep in view the conditions easiest to forget while writing — the rubric defines each one and its exact threshold:

• it is claimed only by a full-depth review;
• a behavioral probe must have run (outcome-correctness, not just an unblocked workflow, for any skill encoding domain claims); and
• a gate-fragile score (one plausible check flip would drop it below the gate) requires an ensemble review before the bar can be claimed.

Safety / Constraints (non-negotiable)

• Never read, request, or paste secrets (.env, API keys, tokens, private keys, credentials).
• Only write inside the user-specified skill directory. If the target path is unclear, ask.
• Do not run commands that modify the repo unless the user explicitly asked for those changes.
• Do not browse the web or call external systems unless the user explicitly requests it.
• Do not execute untrusted code in the target repo (scripts/binaries/tests) unless the user explicitly asks and you can justify the risk.
• Third-party tools that download and execute code (e.g., agnix) run only with explicit user opt-in and a pinned version.
• If the skill being written can perform destructive actions, add explicit confirmation gates and “never do” rules, and declare the narrowest allowed-tools the workflow actually uses (unused write/exec tools are a P1 safety blocker).

Portability Requirement (Codex + Claude Code/Desktop + OpenCode)

Write skill instructions in capability language (search/read/edit/run commands) and avoid hard-coding one vendor’s tool names. If mentioning a product-specific tool, provide a short adapter note (“if unavailable, use shell + rg/sed”). For portability guidance, use [references/portability.md](references/portability.md).

Workflow (decision-complete)

Update mode (keep diffs small)

If the user asked to update an existing skill (not create a new one):

• Change only the requested parts; do not rewrite unrelated sections for style.
• Preserve existing behavior unless it is a spec violation or causes mis-triggering.
• Prioritize: trigger precision (description “when to use”), safety/guardrails, validation loop, then token efficiency.

1) Intake (ask only what matters)

Collect:

• Skill name — hyphen-case; prefer gerund form (writing-x, reviewing-y) per naming guidance.
• What it does (1 sentence)
• When to use (concrete triggers: file types, paths, scenarios) — and when not to (name the sibling skill instead).
• Inputs/outputs (artifacts produced)
• Safety constraints (read-only? destructive ops? secrets? web browsing?)
• Resources needed: scripts/ vs references/ vs assets/

2) Skill Split Proposal (prevent mega-skills)

Before writing anything, produce a short proposal:

• Should this be one skill or multiple?
• Recommend companion skills when appropriate, e.g.:
• reviewer/critic skill (grading, audits)
• installer skill (wiring tools or repo integration)
• domain-reference skill (big schemas or policies)

Rule of thumb:

• If the request spans multiple disjoint workflows, split.
• If the skill needs deterministic, repeatable logic, add a scripts/ helper.

3) Design to the rubric (author toward the score)

Classify before writing, then spend the SKILL.md budget where the weights and critical checks are. The rubric grades by archetype-weighted dimensions — pick the archetype and write to its profile (reviewing-skills/references/skills-rubric.md, “Archetype profiles”):

• Workflow (default) — process skills; workflow quality + spec compliance dominate.
• Reference/Knowledge — curated facts/patterns; token efficiency dominates (≈25%).
• Tool-wrapper — wraps scripts/CLIs; safety + evaluability dominate (≈40% combined).
• Orchestrator — composes skills/agents; loop quality + hand-offs dominate.

If a skill is genuinely between two archetypes, author to the higher-weighted profile of the two and note the ambiguity — the critic scores under both profiles and reports if the grade flips (rubric, "Archetype profiles").

Two checks are critical — a FAIL caps that dimension at 3.0 no matter how tidy the prose, so satisfy them first:

• Triggerable — a strong positive trigger exists (Dimension 2). You will self-test it in Step 5.
• Verifiable success — a stated way to tell the skill worked: eval scenario, acceptance check, or expected output (Dimension 6).

Also classify the invocation model — dispatched (default), user-invoked (disable-model-invocation: true), or both — it re-scopes how triggering is judged.

4) Scaffold the skill directory

Create the skill directory under the user-specified path:

• /SKILL.md — use [references/skill-skeleton.md](references/skill-skeleton.md) as the template
• /agents/openai.yaml — include interface.display_name, short_description (25–64 chars), and default_prompt (must mention $)
• Resource subdirs (scripts/, references/, assets/) — only create the ones you will use
• If the skill acts (writes/runs/network), declare the narrowest allowed-tools it needs — no unused write/exec tools.

Prefer minimal resources. Validation is expected to fail until you fill in the TODOs in Step 5.

5) Write SKILL.md (core)

Use [references/skill-skeleton.md](references/skill-skeleton.md) as the canonical outline.

Hard requirements:

• Frontmatter description covers what + when to use, and stays proportional to its information content — it loads into every session as a permanent token cost.
• Include guardrails and explicit “do not do” rules when relevant.
• Include validation loops (what to check after writing/running).
• Ship eval material: at least one concrete input + a checkable expected output, exercised by a workflow validation step. Decorative scenarios (no expected output, never referenced) fail the rubric and count as bloat — make it real or omit it.
• Calibrate degrees of freedom: a step is fragile when a small wording change breaks the output or correctness can't be eyeballed (parsing, formatting, exact CLI flags, version pins) — give it an exact command/template. A step is heuristic when a competent agent can pick among acceptable options — give it judgment plus acceptance criteria.
• Keep SKILL.md lean: body under ~500 lines (far fewer preferred — it is measured); move bulk examples/specs to references/.

Engineer the description for routing (highest-leverage element — a critical check, stress-tested by a trigger battery):

• Lead with strong positive triggers: artifact types, file patterns, concrete scenarios.
• Add negative triggers — when NOT to use, naming the sibling skill to use instead.
• Avoid generic discovery terms ("helper", "utils") without specifics.
• Scan for collisions: compare against visible sibling skills' descriptions; if a dispatcher could misroute between them, sharpen the boundary in both descriptions.
• Self-test: draft ~5 in-scope and ~5 adjacent out-of-scope prompts and confirm each routes to (or away from) this skill. Fix the description for every misroute.

See [references/worked-examples.md](references/worked-examples.md) for a strong-vs-weak description and a golden mini-skill.

Do not write (rubric auto-penalties):

• Vague directives: "as appropriate", "best practices", "use standard approach".
• Time-sensitive claims ("latest", "current pricing") unless the skill browses the web and says so.
• Windows-style paths; assumed package installs; many options with no default.
• Self-praise as evidence ("battle-tested", "production-grade").

6) Add resources (only if they buy reliability)

Use [references/resource-patterns.md](references/resource-patterns.md):

• Put deterministic logic in scripts/ with a stable CLI.
• Put large but needed knowledge in references/ (loaded on demand).
• Put templates/boilerplate in assets/.

7) Validate (hard gate)

skillcheck (project rules — first-party linter):

• Inside this repo with packages/skillcheck/dist/ present: node packages/skillcheck/bin/skillcheck.js
• Inside this repo without dist/: cd packages/skillcheck && npm install && npm run build, then run the above.
• Outside this repo: npx @jkeskikangas/skillcheck@0.2.4 (pinned). There is no unscoped skillcheck package — do not run npx skillcheck (it resolves to an unrelated package). If unavailable, run the deterministic checks manually and note the fallback.

agnix (specification rules — third-party linter that downloads and executes code):

• Run only with explicit user opt-in and pinned to a specific released version you have vetted — never unpinned (a bare npx agnix pulls latest and can execute changed code). Disclose the external execution in the deliverable. If the user declines, skip it and note the gap.

Fix all reported errors before proceeding. Each linter collects every violation in a single run.

8) Quality Gate

Review after validation. Target: the rubric's meets_bar (Quality Bar above). You authored against the rubric and its vignettes, so optimizing only to them is Goodhart-prone — two defenses are non-negotiable: a user-outcome pre-check (Phase 0) and a held-out probe the score cannot absorb (Phase 2).

Phase 0: User-outcome pre-check (a skill can pass the rubric and still be bad)

Before any scoring, answer in one short trace, independent of the rubric: handed this skill and a real in-scope task, would a user get a correct, faster outcome than without it? If you cannot produce a concrete passing trace — or the honest answer is "it satisfies the checklist but wouldn't actually help" — the skill is not done at any score. Fix the skill, not the trace. Record this judgment in the deliverable.

Phase 1: Self-critic (cheap catch-pass — cannot claim the bar)

You are author-contaminated, so this pass only catches obvious holes: a fail here is actionable, a pass proves nothing. Re-read SKILL.md and check for:

• Vague or missing "when to use" triggers; trigger collisions with siblings.
• Missing guardrails for destructive/network actions; over-broad allowed-tools.
• Missing eval material / no stated way to verify success.
• Bloated prose that should be bullets or moved to references/.
• Workflow steps that leave key decisions ambiguous.

Fix what is fixable inline; flag what needs re-analysis or user input. Then go to Phase 2 — only a fresh context can claim the bar.

Phase 2: Fresh-context critic (claims the bar)

Run $reviewing-skills in a fresh context (its scores are blind only without your authoring context):

• If your environment supports subagents, spawn a fresh-context subagent and give it the skill path.
• Held-out signal (critic-owned; you never see the probe): the held-out probe is synthesized and run by $reviewing-skills in its fresh context, not by you — you request the gate, you do not author, read, select, or get shown the probes (the protocol lives in reviewing-skills/references/holdout-probes.md; it is the critic's, not an authoring target). The critic returns only a pass/fail and a redacted symptom for any failure; fix the skill against that symptom — you cannot tune to the probe because you never see one. A held-out FAIL arrives as a P1 finding and is therefore below-bar regardless of the weighted score. Never treat the rubric or its canonical vignettes as authoring targets.
• Independence guard — claiming the bar needs a fresh context. If you must run $reviewing-skills inline (no subagent) or self-review (critic unavailable), the verdict is author-contaminated: you may not assert meets_bar / "professional-grade". Mark the result bar-unclaimed, list which independence guarantees degraded, and recommend a separate-session review.
• If the skill is git-tracked and you changed it, require the critic to cite the relevant diff hunk or commit short-hash for any change-driven P1/P2 findings.

Drive the loop with the critic's machine-readable verdict — do not re-review from scratch each pass:

1. First iteration: full review → consume the JSON findings array; apply fixes by id, P1 then P2 (P3 last). Do not comply blindly: if you judge a finding a false positive, re-open its cited evidence first; if it does not reproduce, record a dispute note and ask the critic to re-examine that check (verdict-stability) rather than mutating the skill to satisfy a phantom finding.
2. Between iterations: re-run $reviewing-skills in triage depth (blockers/P1 only — cheap) or incremental depth (diff-scoped scores against the prior reviewed_commit).
3. Re-run validation after each fix round.
4. Finish with a full review to confirm meets_bar — triage/incremental can never claim the gate.

Repeat up to 3 loops; stop early when the bar is met or two consecutive iterations show no score improvement (plateau). Match rigor to stakes: a low-stakes skill may need only one full review; reserve the full ladder (and ensemble) for gated or shared skills.

9) Finalize

If the final full review did not return meets_bar: true — a plateau or loop-cap stop, an unresolved P1, a failed Phase 0, a held-out-probe failure, or a bar-unclaimed contaminated verdict — the skill is below bar. You MUST NOT present it as done or “professional-grade”: lead the deliverable with BELOW BAR — and the smallest remaining change. Do not let the agents/openai.yaml “until it reaches an A grade” framing imply a success it did not reach.

On a met bar, deliver:

• The final skill folder path(s)
• Any suggested follow-on skills (from the split proposal)
• A short note on why the skill will trigger correctly (tie to description “when to use”), including the Step 5 self-test routing result and the Phase 0 user-outcome trace.

Edge Cases

• User provides no skill name or path: ask before proceeding; do not guess.
• Target directory already has a SKILL.md: enter update mode; do not overwrite without confirmation.
• Linters not available (no Node.js / npx): warn the user; skip validation but note it was skipped in the deliverable.
• $reviewing-skills not available: self-review against the 7 dimensions, mark the result bar-unclaimed, and state in the deliverable that no fresh-context critic ran (a contaminated self-review cannot claim meets_bar/professional-grade).

Eval

This skill's own check (exercised by Step 5 and Step 8):

• Input: the rough prompt “make my SQL queries faster”, with no skill name or path given.
• Expected output: Step 1 asks for a skill name/path before scaffol

…

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: jkeskikangas
• Source: jkeskikangas/skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.