rstack-skill-evaluator

A benchmarking and improvement guide for coding-agent skills. It compares an agent using a skill with one without it, then records test results and suggested improvements.

In plain words
What is it for?
Use it to create evaluation cases, run comparisons with Codex or Claude Code, grade the outcomes, and save benchmark reports for a named skill.
Why use it?
It helps determine whether a skill actually improves agent results instead of relying on impressions. It also keeps evaluation data and reports organized.

Skill for Claude CodeCodex

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/rstackjs/agent-skills/rstack-skill-evaluator
Any agent
npx skills add rstackjs/agent-skills --skill rstack-skill-evaluator
Clone the repo
git clone --depth 1 https://github.com/rstackjs/agent-skills

Made for: Claude Code, Codex.

Per session 48 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,090 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 $0.00048 $0.01090
Opus 5 $0.00024 $0.00545
Sonnet 5 $0.00010 $0.00218
Haiku 4.5 $0.00005 $0.00109

Measured 2d ago against content hash 2bf12eeeae0c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

rstack-skill-evaluator 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.

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.

.agents/skills/rstack-skill-evaluator/SKILL.md · 70 lines

How it starts

The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Rstack Skill Evaluator

A repo-specific compatibility layer on top of skill-creator. Reuse its Test / Improve / Benchmark concepts, JSON schemas, grading guidance, and eval viewer, but select the executor for the current environment.

Select the executor

  • When the user requests Codex or codex is the available CLI, read references/codex-cli.md and follow it. Its instructions override Claude-specific commands and subagent mechanics in skill-creator.
  • Otherwise, follow skill-creator directly.

Do not invoke skill-creator/scripts/run_eval.py, run_loop.py, or improve_description.py in Codex mode. Those scripts shell out to claude -p and test Claude-specific skill discovery. Provider-neutral utilities such as quick_validate.py, aggregate_benchmark.py, and eval-viewer/generate_review.py can be reused after validating the installed dependency version.

Targeting a skill

If the user hasn't named a target, ask. Skills live under skills/ (production) and .agents/skills/ (internal-only).

Before editing an existing skill, snapshot it so the next iteration can compare the candidate against the previous version. Keep the snapshot and all raw run data outside tracked artifact paths.

Minimum eval rules

Use these rules for a basic eval unless the user requests a larger benchmark:

  1. Define at least two realistic cases: one representative workflow and one boundary, failure, or constraint case. Prefer a third case when the skill has multiple distinct modes.
  2. Give each case 2-5 outcome-focused assertions that can be verified from files, command results, or other durable evidence. Do not reward an agent merely for saying it succeeded.
  3. Run every case as a matched pair on fresh, identical fixture copies: with_skill and without_skill. When improving an existing skill, also compare the candidate against the snapshotted previous version when that is the more useful baseline.
  4. Keep the task prompt and runtime controls identical across configurations. The only intended difference is access to the target skill. Do not expose assertions, expected grader decisions, or another run's outputs to the executor.
  5. Use a fresh session for every run. Pin and record the CLI version, model, sandbox, approval, network, and relevant config. Never reuse a mutated working copy.
  6. Grade both configurations with the same checks. Prefer deterministic scripts for objective assertions; use an independent grader only for semantic checks, and require concrete evidence for every pass.
  7. Treat CLI crashes, timeouts, missing fixtures, and auth failures as harness failures, not skill failures. Fix or clearly report the harness problem before drawing skill conclusions.
  8. One run per configuration is a smoke eval. Use at least three repetitions before making claims about reliability, variance, token cost, or wall-time improvements.

Read the full file on GitHub · 70 lines

Files

What ships with it

2 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 · 70 lines · 48 tokens per session scan A 2bf12eeeae0c

Subscribe to this mod's changes

rstack-skill-evaluator is a skill published in the GitHub repository rstackjs/agent-skills (90 stars, last pushed 6d ago), licensed MIT. It adds 48 tokens to every session and 1,090 once invoked, about $0.0002 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 2026-08-30.