eval-regression

eval-regression is a skill for Claude Code from reidemeister94/development-skills. It costs 31 tokens per session (538 once invoked), scanned A, original, MIT.

A procedure for checking whether a coding-agent plugin or skill has changed its behaviour or introduced a regression. It uses repository tests and selected evaluation cases rather than assuming every case must run.

In plain words
What is it for?
Use it when reviewing plugin changes, comparing behaviour with a previous revision, selecting affected evaluation cases, or reporting failed checks and timeouts.
Why use it?
It makes the check reproducible and requires approval before running potentially costly agent evaluations.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter. Also seen: names the AskUserQuestion tool; mentions Codex.

Part of the development-skills plugin — 16 skills, 1 agent, 2 hooks shipped together

Good fit Use it when reviewing plugin changes, comparing behaviour with a previous revision, selecting affected evaluation cases, or reporting failed checks and timeouts.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/reidemeister94/development-skills/eval-regression
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.

Any agent
npx skills add reidemeister94/development-skills --skill eval-regression
Clone the repo
git clone --depth 1 https://github.com/reidemeister94/development-skills

Made for: Claude Code.

Or install development-skills, the plugin that ships this one along with the rest of its 16 skills, 1 agent, 2 hooks.

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 eval-regression

README.md
[![agentmods](https://agentmods.dev/badge/skills/reidemeister94/development-skills/eval-regression.svg)](https://agentmods.dev/skills/reidemeister94/development-skills/eval-regression)
Your own site
<a href="https://agentmods.dev/skills/reidemeister94/development-skills/eval-regression"><img src="https://agentmods.dev/badge/skills/reidemeister94/development-skills/eval-regression.svg" alt="Measured on agentmods" height="20"></a>
Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 538 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 $0.00031 $0.00538
Opus 5 $0.00015 $0.00269
Sonnet 5 $0.00006 $0.00108
Haiku 4.5 $0.00003 $0.00054

Measured 7d ago against content hash 7ba5eb7c74c5, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

eval-regression 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 7d 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/eval-regression/SKILL.md · 32 lines

How it starts

The opening of the file, as written. The whole thing — 32 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Eval regression

Use deterministic repository tests first. Stop when the target has no behavioral diff.

Resolve the plugin from the argument or cwd. Its catalog is evals/evals.json; the shared runner is ../ai-agent-bench/scripts/run_evals.py. Require the user to choose agent, model, and effort. Never select a costly model or high effort silently.

Normal check

  1. Select cases by changed paths with --changed-from <base>, or name them with --case. Do not select the full catalog implicitly.
  2. Run the command without --run. The runner prints the cases, modes, repeat count, session count, per-session timeout, and maximum duration without starting an agent.
  3. Present that plan and stop for explicit cost approval.
  4. After approval, repeat the same command with --run. The default is candidate-only, one run per case, 180 seconds per session, and at most four sessions.
  5. Report every failed assertion, timeout, non-zero exit, duration, and token count. Missing evidence is inconclusive.

Escalation

  • Compare base and candidate only when the user asks, or when a failed candidate check needs to distinguish a regression from an existing failure. Extract the base with git archive; run the same selected cases, agent, model, effort, repeat, and timeout on both; compare reports with --compare.
  • Repeat only a failed or observably unstable case. Three repeats are a stability benchmark, not a default.
  • --all, --repeat > 1, a larger --max-sessions, or a longer timeout needs a new run plan and explicit approval.
  • Routing cases stop at the first Skill selection. A tool assertion is appropriate there because routing is the contract; they must not execute the selected skill.

Remove temporary base copies after the comparison. Do not edit or commit the target.

Deterministic assertions are tool, tool_not, clean_worktree, changed_files_exact, file_contains, file_not_contains, transcript_contains, and tool_sequence. Use a semantic judge only when no filesystem, command, tool, ordering, or assistant-output observation can express the contract.

Read the full file on GitHub · 32 lines

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. 7d ago First seen · 32 lines · 31 tokens per session scan A 7ba5eb7c74c5

Subscribe to this mod's changes

eval-regression is a skill published in the GitHub repository reidemeister94/development-skills (11 stars, last pushed 1mo ago), licensed MIT. It adds 31 tokens to every session and 538 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.

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