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skill-optimizer

skill-optimizer is a skill for Claude Code from fastxyz/skill-optimizer. It costs 52 tokens per session (2,349 once invoked), scanned A, original, MIT.

An evaluation workbench for testing AI-agent skills. It runs user-like tasks in an isolated Docker workspace, records the agent's actions, and grades the resulting files or other outcomes.

In plain words
What is it for?
Use it to create and run evaluation cases and suites, test skills across models, inspect traces, and use deterministic graders to check results.
Why use it?
It helps you measure whether a skill works reliably instead of judging it from a few conversations. The recorded trace also helps investigate failures.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: mentions .claude-plugin; mentions Claude Code; mentions Codex.

Needs its repository: it runs a file that does not travel with it, so clone the repository first. The line is node dist/cli.js --help.

Part of the skill-optimizer plugin — 2 skills shipped together

not rated 82repo 5mo ago A scan 52 tokens original MIT

Good fit Use it to create and run evaluation cases and suites, test skills across models, inspect traces, and use deterministic graders to check results.

Compare 6 skills from other repositories ↓
View source ↗ fastxyz/skill-optimizer
Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo
git clone --depth 1 https://github.com/fastxyz/skill-optimizer
agentmods
npx agentmods add skills/fastxyz/skill-optimizer/skill-optimizer

Made for: Claude Code.

Or install skill-optimizer, the plugin that ships this one along with the rest of its 2 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for skill-optimizer

README.md
[![agentmods](https://agentmods.dev/badge/skills/fastxyz/skill-optimizer/skill-optimizer/github.svg)](https://agentmods.dev/skills/fastxyz/skill-optimizer/skill-optimizer)
Your own site
<a href="https://agentmods.dev/skills/fastxyz/skill-optimizer/skill-optimizer"><img src="https://agentmods.dev/badge/skills/fastxyz/skill-optimizer/skill-optimizer/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for skill-optimizer

Your own site · 80×15
<a href="https://agentmods.dev/skills/fastxyz/skill-optimizer/skill-optimizer"><img src="https://agentmods.dev/badge/skills/fastxyz/skill-optimizer/skill-optimizer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,349 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00052 $0.02349
Opus 5.5 $0.00021 $0.00940
Sonnet 5.5 $0.00010 $0.00470
Haiku 4.5 $0.00005 $0.00235

Measured 2mo ago against content hash 8875c9505df1, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

skill-optimizer 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 2mo ago.

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-optimizer/SKILL.md · 211 lines

How it starts

The opening of the file, as written. The whole thing — 211 lines — stays where its author put it; the contents beside it link to each section on GitHub.

skill-optimizer

skill-optimizer is an eval workbench for agent skills. It runs a model in an isolated Docker /work directory, provides skills/references as normal workspace files, captures an agent trace, and grades deterministic local outcomes.

Use this skill as the source of truth for authoring eval suites in this repo. Detailed schema and patterns are in references/workbench.md.

Core Model

  • A case is one user-like task plus one or more deterministic graders.
  • A suite is a set of cases and OpenRouter models to run as a matrix.
  • references are copied into /work before the agent starts; this is where eval skills live.
  • The agent phase sees /work only. It cannot see /case, /results, graders, hidden answers, or hidden metadata.
  • Cases can define mcpServers; these are exposed through a workbench mcp command during the agent phase.
  • Graders run after the agent with /case, /work, and /results mounted.
  • trace.jsonl is the debugging source for what the agent saw, said, and did.

Commands

Goal Command
Install deps npm install
Build CLI npm run build
Run one case npx tsx src/cli.ts run-case <case.yml>
Run one case across models npx tsx src/cli.ts run-case <case.yml> --models openrouter/google/gemini-2.5-flash,openrouter/openai/gpt-5.4
Run a suite npx tsx src/cli.ts run-suite <suite.yml>
CLI help npx tsx src/cli.ts --help

Rules:

  • Use only openrouter/... model refs.
  • OPENROUTER_API_KEY is required for real model runs.
  • run-suite uses models: from suite.yml; it has no model override flag.
  • run-case can use its case model: or --model / --models.
  • Docker image default is skill-optimizer-workbench:local.

Install This Skill

This repository ships one canonical skill at skills/skill-optimizer/SKILL.md plus plugin metadata for Claude Code, OpenCode, Codex, Cursor, and Gemini.

Install the skill for common agents with:

npx skills add fastxyz/skill-optimizer --skill skill-optimizer -a claude-code -a opencode -a codex -a cursor

Read the full file on GitHub · 211 lines

Files

What ships with it

1 file 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. 2mo ago First seen · 211 lines · 52 tokens per session scan A 8875c9505df1

Subscribe to this mod's changes

skill-optimizer is a skill published in the GitHub repository fastxyz/skill-optimizer (82 stars, last pushed 5mo ago), licensed MIT. It adds 52 tokens to every session and 2,349 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-08-30.

Building agentsEvaluationTestingaiai-agentai-skillbenchmarkcli
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