agentmods.dev

skill-creator

A development skill for creating, editing, and improving skills that guide coding agents. It uses test prompts and evaluations to check whether a skill works as intended.

In plain words
What is it for?
Use it to build a new agent skill, revise an existing one, run evaluations, compare performance, and improve how the skill is triggered.
Why use it?
It gives skill authors a repeatable way to find unclear instructions and improve results based on evidence instead of guesswork.

Skill for Claude CodeCodex

5 2mo ago A scan 63 tokens original MIT
View the source file MatthewYe/opencode-toolbox
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/matthewye/opencode-toolbox/skill-creator
Any agent
npx skills add MatthewYe/opencode-toolbox --skill skill-creator
Clone the repo
git clone --depth 1 https://github.com/MatthewYe/opencode-toolbox

Made for: Claude Code, Codex.

Per session 63 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,486 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00063 $0.05486
Opus 5 $0.00032 $0.02743
Sonnet 5 $0.00013 $0.01097
Haiku 4.5 $0.00006 $0.00549

Measured 2d ago against content hash e65817752ce3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

skill-creator scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

The scan reads SKILL.md. This mod also ships 18 executable files (eval-viewer/__tests__/generate_review.test.ts, eval-viewer/generate_review.ts, scripts/__tests__/aggregate_benchmark.test.ts, …), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/skill-creator/SKILL.md · 455 lines

How it starts

The opening of the file, as written. The whole thing — 455 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill Creator

A skill for creating new skills and iteratively improving them.

At a high level, the process of creating a skill goes like this:

  • Decide what you want the skill to do and roughly how it should do it
  • Write a draft of the skill
  • Create a few test prompts and run the agent with access to the skill on them
  • Help the user evaluate the results both qualitatively and quantitatively
    • While the runs happen in the background, draft some quantitative evals if there aren't any. Explain them to the user.
    • Use bun run skills/skill-creator/eval-viewer/generate_review.ts to show the user the results, and let them review both qualitative and quantitative metrics
  • Rewrite the skill based on feedback from the user's evaluation of the results
  • Repeat until you're satisfied
  • Expand the test set and try again at larger scale

Your job is to figure out where the user is in this process and help them progress through these stages.

OpenCode Skill Conventions

OpenCode skills follow the agentskills.io specification:

Frontmatter

  • name (required): lowercase alphanumeric + single hyphens, 1-64 chars. Must match the directory name. Regex: ^[a-z0-9]+(-[a-z0-9]+)*$
  • description (required): 1-1024 chars. Describe what it does AND when to trigger. Written in third person. Use the pattern "What it does. Use when [specific triggers]."
  • compatibility (optional): e.g., opencode
  • metadata (optional): string-to-string map for extra metadata

Discovery

OpenCode discovers skills from these locations:

  • .opencode/skills/<name>/SKILL.md
  • ~/.config/opencode/skills/<name>/SKILL.md
  • .claude/skills/<name>/SKILL.md, ~/.claude/skills/<name>/SKILL.md
  • .agents/skills/<name>/SKILL.md, ~/.agents/skills/<name>/SKILL.md
  • Plugin-injected paths via config.skills.paths

Loading mechanism

Skills appear in the skill tool's <available_skills> block. The agent reads descriptions and invokes the skill tool to load a skill. After the iteration loop is complete and the skill is ready, offer to package it.

Read the full file on GitHub · 455 lines

Files

What ships with it

57 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 455 lines · 63 tokens per session scan A e65817752ce3

Subscribe to this mod's changes

skill-creator is a skill published in the GitHub repository MatthewYe/opencode-toolbox (5 stars, last pushed 2mo ago), licensed MIT. It adds 63 tokens to every session and 5,486 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Building agentsTesting
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