check

check is a skill for Claude Code, Codex from JuliusBrussee/cavekit. It costs 102 tokens per session (771 once invoked), scanned A, original, MIT.

A read-only checker that compares a written SPEC.md file with the current code. It reports where requirements, interfaces, or task statuses no longer match.

In plain words
What is it for?
Use it to audit invariants, interfaces, and completed tasks, with findings grouped by severity and supported by file and line evidence.
Why use it?
It finds specification drift—the gradual difference between what the project says it should do and what the code actually does—without changing files.

Skill for Claude CodeCodex

Part of the ck plugin — 8 skills, 7 commands shipped together

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/juliusbrussee/cavekit/check
Any agent
npx skills add JuliusBrussee/cavekit --skill check
Clone the repo
git clone --depth 1 https://github.com/JuliusBrussee/cavekit

Made for: Claude Code, Codex.

Or install ck, the plugin that ships this one along with the rest of its 8 skills, 7 commands.

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 check

README.md
[![agentmods](https://agentmods.dev/badge/skills/juliusbrussee/cavekit/check.svg)](https://agentmods.dev/skills/juliusbrussee/cavekit/check)
Your own site
<a href="https://agentmods.dev/skills/juliusbrussee/cavekit/check"><img src="https://agentmods.dev/badge/skills/juliusbrussee/cavekit/check.svg" alt="Measured on agentmods" height="20"></a>
Per session 102 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 771 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 $0.00102 $0.00771
Opus 5 $0.00051 $0.00385
Sonnet 5 $0.00020 $0.00154
Haiku 4.5 $0.00010 $0.00077

Measured 4d ago against content hash 6daabb7099f2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

check 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 4d 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/check/SKILL.md · 94 lines

How it starts

The opening of the file, as written. The whole thing — 94 lines — stays where its author put it; the contents beside it link to each section on GitHub.

check — drift report

Pure diagnostic. Reports violations. Writes nothing. User decides remedy.

Spec drifting silently from code is the #1 SDD failure mode. check is the detector. Run it after each /build and before each ship — drift caught here is a diff; drift caught in prod is a §B.

LOAD

  1. Read SPEC.md. If missing → "no spec, nothing to check." Stop.
  2. Parse invocation args:
    • §V → check invariants only (default)
    • §I → check interfaces
    • §T → audit task status vs code
    • --all → all three

CHECK §V — invariants

For each V:

  1. Translate invariant into verifiable claim about code.
  2. Grep / read relevant files.
  3. Classify: HOLD / VIOLATE / UNVERIFIABLE.
  4. Record address + file:line evidence.

CHECK §I — interfaces

For each I item:

  1. Locate implementation.
  2. Classify:
    • MATCH — shape in code = shape in spec.
    • DRIFT — impl exists, shape differs.
    • MISSING — impl absent.
    • EXTRA — code exposes surface not in §I.

CHECK §T — tasks

For each T:

  1. If x: verify claimed work present.
  2. If ~: note as in-progress.
  3. If .: note as pending.
  4. Flag x rows with no evidence as STALE.

REPORT

Caveman. Grouped by severity.

## §V drift
V2 VIOLATE: auth/mw.go:47 uses `<` not `≤`. see §B.1.
V5 UNVERIFIABLE: no test covers ∀ req path.

## §I drift
I.api DRIFT: POST /x returns `{result}` not `{id}`. route.go:112.
I.cmd MISSING: `foo bar` absent from cli/*.go.

## §T drift
T3 STALE: status `x`, no middleware file exists.

## summary
2 violate. 1 missing. 1 stale. 1 unverifiable.
next: spec skill with `bug:` or fix code at cited lines.

REMEDY HINTS (not actions)

End report with one-line hint per class:

  • VIOLATE / DRIFT → invoke spec skill bug: <V.n> or fix code.
  • MISSING → invoke build skill on §T.n if task exists; else spec skill amend §T.
  • STALE → spec skill amend §T to uncheck.
  • EXTRA → spec skill amend §I to document, or delete code.

Never invoke fixes. Report only.

Read the full file on GitHub · 94 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. 4d ago First seen · 94 lines · 102 tokens per session scan A 6daabb7099f2

Subscribe to this mod's changes

check is a skill published in the GitHub repository JuliusBrussee/cavekit (1,141 stars, last pushed 19d ago), licensed MIT. It adds 102 tokens to every session and 771 once invoked, about $0.0005 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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