check-impl-against-spec

check-impl-against-spec is a skill for Claude Code, Codex from warpdotdev/common-skills. It costs 44 tokens per session (498 once invoked), scanned A, original, MIT.

A review aid for comparing a pull request with the approved requirements and implementation notes in spec_context.md. A pull request is a proposed set of code changes for review.

In plain words
What is it for?
Reading the specification, checking the pull-request diff and repository files, and recording important mismatches in review.json.
Why use it?
It helps identify material differences between what was agreed and what the code actually does, without treating harmless implementation details as problems.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: installed under .agents/ (shared by several agents).

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/warpdotdev/common-skills/check-impl-against-spec
Any agent
npx skills add warpdotdev/common-skills --skill check-impl-against-spec
Clone the repo
git clone --depth 1 https://github.com/warpdotdev/common-skills

Made for: Claude Code, Codex.

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-impl-against-spec

README.md
[![agentmods](https://agentmods.dev/badge/skills/warpdotdev/common-skills/check-impl-against-spec.svg)](https://agentmods.dev/skills/warpdotdev/common-skills/check-impl-against-spec)
Your own site
<a href="https://agentmods.dev/skills/warpdotdev/common-skills/check-impl-against-spec"><img src="https://agentmods.dev/badge/skills/warpdotdev/common-skills/check-impl-against-spec.svg" alt="Measured on agentmods" height="20"></a>
Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 498 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 5.1 $0.00044 $0.00498
Opus 5 $0.00022 $0.00249
Sonnet 5 $0.00009 $0.00100
Haiku 4.5 $0.00004 $0.00050

Measured 6d ago against content hash c0e5d80739ae, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

check-impl-against-spec 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 6d 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

.agents/skills/check-impl-against-spec/SKILL.md · 50 lines

How it starts

The opening of the file, as written. The whole thing — 50 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Check implementation against spec

Use this skill only when spec_context.md exists during PR review.

Goal

Determine whether the implementation in the checked-out PR materially matches the approved spec context. This is a supplement to the normal code review, not a separate output.

Inputs

  • spec_context.md contains the spec context to compare against. It may include both product spec content (intended behavior, acceptance criteria) and tech spec content (implementation details, file changes).
  • pr_diff.txt contains the annotated diff for the PR.
  • pr_description.md may contain additional scope or rationale.
  • The working tree contains the PR branch contents.

Process

  1. Read spec_context.md and extract the concrete commitments it makes:
    • required behaviors (from the product spec)
    • required files or subsystems to change (from the tech spec)
    • stated constraints
    • required follow-up steps, validation, or migrations
  2. Compare those commitments against the actual implementation in pr_diff.txt and the checked-out files.
  3. Treat small implementation-level adjustments as acceptable when they preserve the spec's intent. Do not flag harmless differences in naming, structure, or low-level technique.
  4. Flag a mismatch only when it is material, such as:
    • required behavior in the product spec is missing
    • the implementation contradicts a spec decision
    • the change introduces significant unplanned scope
    • a required validation, migration, or compatibility step from the tech spec is absent

Outputs

  • Do not create a separate report file.
  • Fold spec-alignment findings into review.json.
  • Put broad spec-drift concerns in the review summary.
  • Add inline comments only when the mismatch can be tied to changed lines in the diff.
  • Treat material spec drift as at least an important concern.
  • If the implementation matches the spec closely enough, do not add comments just to mention alignment.

Boundaries

  • Do not require literal one-to-one implementation of the spec when the PR achieves the same outcome safely.
  • Do not speculate about spec details that are not actually present in spec_context.md.
  • Do not post to GitHub directly.

Read the full file on GitHub · 50 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. 6d ago First seen · 50 lines · 44 tokens per session scan A c0e5d80739ae

Subscribe to this mod's changes

check-impl-against-spec is a skill published in the GitHub repository warpdotdev/common-skills (530 stars, last pushed 2d ago), licensed MIT. It adds 44 tokens to every session and 498 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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