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Code Review

Free

Automate code reviews against standards and specs.

by mattpocock212.7k stars on mattpocock/skills
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Updated Aug 6, 2026
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Free · Opens the source repo

What Code Review does

The Code Review skill enables developers to efficiently assess code changes by comparing them against a specified fixed point, such as a commit, branch, or tag. This skill operates along two distinct axes: Standards and Spec. The Standards axis evaluates whether the code adheres to the repository's documented coding standards, while the Spec axis checks if the code accurately implements the requirements outlined in the originating issue or specification. By running these evaluations in parallel, the skill ensures that the context for each review remains clean and focused, providing clear and actionable feedback.

To initiate a review, users simply specify a fixed point, and the skill captures the necessary diff and commit information. It then identifies the relevant specifications and standards documentation available in the repository. If any discrepancies are found, the skill aggregates the findings from both the Standards and Spec reviews and presents them side by side. This structured approach allows developers to quickly identify areas of improvement, whether they relate to coding practices or alignment with project requirements.

This skill is particularly useful for teams looking to maintain high code quality and ensure compliance with established coding conventions. It can be employed during pull requests, branch reviews, or any situation where changes need to be evaluated against both coding standards and project specifications. By automating these reviews, developers can save time and reduce the cognitive load associated with manual code assessments.

However, it's important to note that this skill relies on the presence of appropriate documentation within the repository. If the necessary standards or specifications are not available, the effectiveness of the review may be limited. Additionally, while the skill provides valuable insights, it is not a substitute for human judgment in assessing the overall quality and intent of the code changes.

When to use it

Use this skill when reviewing branches, pull requests, or any work-in-progress changes to ensure compliance with coding standards and specifications.

When not to use it

This skill may not be suitable if the repository lacks documentation on coding standards or specifications, as it relies on these sources for effective reviews.

What you can build with it

Reviewing a Pull Request

Use this skill to automatically evaluate a pull request against the repository's coding standards and the associated issue specifications.

Assessing Work-in-Progress Changes

When working on a feature branch, utilize this skill to ensure that ongoing changes comply with project standards before merging.

Conducting Code Quality Audits

Leverage this skill during regular code quality audits to identify potential issues in adherence to coding standards and specifications.

How to install Code Review

View source

1. Install with the skills CLI

npx skills add mattpocock/skills/code-review --agent claude-code

2. Or install it manually

Download the skill folder and drop it into ~/.claude/skills/ for all projects, or .claude/skills/ to scope it to one repo. Restart Claude Code so it picks up the new skill.

Anthropic's agentic coding CLI, and the reference implementation of Agent Skills. Drop a skill folder into ~/.claude/skills and Claude Code loads it automatically whenever a task matches the skill's description. Claude Code docs

Inside SKILL.md

Written by mattpocock

Two-axis review of the diff between HEAD and a fixed point the user supplies:

  • Standards — does the code conform to this repo's documented coding standards?
  • Spec — does the code faithfully implement the originating issue / spec?

Both axes run as parallel sub-agents so they don't pollute each other's context, then this skill aggregates their findings.

The issue tracker should have been provided to you — run /setup-matt-pocock-skills if docs/agents/issue-tracker.md is missing.

Process

1. Pin the fixed point

Whatever the user said is the fixed point — a commit SHA, branch name, tag, main, HEAD~5, etc. If they didn't specify one, ask for it.

Capture the diff command once: git diff <fixed-point>...HEAD (three-dot, so the comparison is against the merge-base). Also note the list of commits via git log <fixed-point>..HEAD --oneline.

Before going further, confirm the fixed point resolves (git rev-parse <fixed-point>) and the diff is non-empty. A bad ref or empty diff should fail here — not inside two parallel sub-agents.

2. Identify the spec source

Look for the originating spec, in this order:

  1. Issue references in the commit messages (#123, Closes #45, GitLab !67, etc.) — fetch via the workflow in docs/agents/issue-tracker.md.
  2. A path the user passed as an argument.
  3. A spec file under docs/, specs/, or .scratch/ matching the branch name or feature.
  4. If nothing is found, ask the user where the spec is. If they say there isn't one, the Spec sub-agent will skip and report "no spec available".

3. Identify the standards sources

Anything in the repo that documents how code should be written, such as CODING_STANDARDS.md or CONTRIBUTING.md.

On top of whatever the repo documents, the Standards axis always carries the smell baseline below — a fixed set of Fowler code smells (Refactoring, ch.3) that applies even when a repo documents nothing. Two rules bind it:

  • The repo overrides. A documented repo standard always wins; where it endorses something the baseline would flag, suppress the smell.
  • Always a judgement call. Each smell is a labelled heuristic ("possible Feature Envy"), never a hard violation — and, like any standard here, skip anything tooling already enforces.

Each smell reads what it ishow to fix; match it against the diff:

  • Mysterious Name — a function, variable, or type whose name doesn't reveal what it does or holds. → rename it; if no honest name comes, the design's murky.
  • Duplicated Code — the same logic shape appears in more than one hunk or file in the change. → extract the shared shape, call it from both.
  • Feature Envy — a method that reaches into another object's data more than its own. → move the method onto the data it envies.
  • Data Clumps — the same few fields or params keep travelling together (a type wanting to be born). → bundle them into one type, pass that.
  • Primitive Obsession — a primitive or string standing in for a domain concept that deserves its own type. → give the concept its own small type.
  • Repeated Switches — the same switch/if-cascade on the same type recurs across the change. → replace with polymorphism, or one map both sites share.
  • Shotgun Surgery — one logical change forces scattered edits across many files in the diff. → gather what changes together into one module.
  • Divergent Change — one file or module is edited for several unrelated reasons. → split so each module changes for one reason.
  • Speculative Generality — abstraction, parameters, or hooks added for needs the spec doesn't have. → delete it; inline back until a real need shows.
  • Message Chains — long a.b().c().d() navigation the caller shouldn't depend on. → hide the walk behind one method on the first object.
  • Middle Man — a class or function that mostly just delegates onward. → cut it, call the real target direct.
  • Refused Bequest — a subclass or implementer that ignores or overrides most of what it inherits. → drop the inheritance, use composition.

4. Spawn both sub-agents in parallel

Standards sub-agent prompt — include:

  • The full diff command and commit list.
  • The list of standards-source files you found in step 3, plus the smell baseline from step 3 pasted in full — the sub-agent has no other access to it.
  • The brief: "Report — per file/hunk where relevant — (a) every place the diff violates a documented standard: cite the standard (file + the rule); and (b) any baseline smell you spot: name it and quote the hunk. Distinguish hard violations from judgement calls — documented-standard breaches can be hard, but baseline smells are always judgement calls, and a documented repo standard overrides the baseline. Skip anything tooling enforces. Under 400 words."

Spec sub-agent prompt — include:

  • The diff command and commit list.
  • The path or fetched contents of the spec.
  • The brief: "Report: (a) requirements the spec asked for that are missing or partial; (b) behaviour in the diff that wasn't asked for (scope creep); (c) requirements that look implemented but where the implementation looks wrong. Quote the spec line for each finding. Under 400 words."

If the spec is missing, skip the Spec sub-agent and note this in the final report.

5. Aggregate

Present the two reports under ## Standards and ## Spec headings, verbatim or lightly cleaned. Do not merge or rerank findings — the two axes are deliberately separate (see Why two axes).

End with a one-line summary: total findings per axis, and the worst issue within each axis (if any). Don't pick a single winner across axes — that's the reranking the separation exists to prevent.

Why two axes

A change can pass one axis and fail the other:

  • Code that follows every standard but implements the wrong thing → Standards pass, Spec fail.
  • Code that does exactly what the issue asked but breaks the project's conventions → Spec pass, Standards fail.

Reporting them separately stops one axis from masking the other.

Frequently asked questions about Code Review

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