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Agent skill

Spec Review

by cashew-labs in cashew-labs/libretto

Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill.

MITAuto-check passedDevelopment

Install Spec Review

skills CLI
$ npx skills add cashew-labs/libretto --skill spec-review -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install cashew-labs/libretto spec-review --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/cashew-labs/libretto.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/spec-review .claude/skills/spec-review && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
spec-review
GitHub stars
904
Token cost
~1.2k tokens
SKILL.md length
653 words
Files
1
Skills in repo
21
Repo updated
First seen
Licence
MIT

At a glance

Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill.

  • Works in 4 steps: Read the spec → Research the codebase → Evaluate → …
  • Asked to review
  • SKILL.md covers Step 1: Read the spec, Step 2: Research the codebase, Step 3: Evaluate and Step 4: Structure your response, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Spec Review is an agent skill from cashew-labs/libretto. Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill. Use when asked to review, critique, or check a spec.

Its SKILL.md is about 1.2k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development. The repository describes itself as: The AI toolkit for building reliable browser automations. The licence is MIT.

When your agent uses it

  • Asked to review

Example prompts

  • “/spec-review”

Workflow steps

4 steps, taken from the step headings in SKILL.md.

  1. Read the spec
  2. Research the codebase
  3. Evaluate
  4. Structure your response

What it can do on your machine

Read from SKILL.md and the folder at commit 41ab782. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are markdown).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Spec Review loads about 1.2k tokens when it runs. Until then it costs about 41 tokens; SKILL.md has 653 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~41
When it runs · the whole SKILL.md, loaded when a task matches
~1.2k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from cashew-labs/libretto at commit 41ab782, republished under its MIT licence (© cashew-labs). 653 words, ~1,209 tokens.

Download SKILL.mdSave it as .claude/skills/spec-review/SKILL.md (or your agent's skills folder).
name
spec-review
description
Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill. Use when asked to review, critique, or check a spec.

Review the spec the user points you to. Follow these steps in order.

Step 1: Read the spec

Read the spec file the user references.

Step 2: Research the codebase

Use sub-agents to read every file listed in the spec's "Important files" section. For each file, understand its current state well enough to evaluate whether the spec's proposed changes are correct and complete.

If the spec references external libraries or APIs, look up their documentation.

Step 3: Evaluate

Assess the spec against three categories. For each finding, cite the specific spec line or section and the relevant source file and line number.

Under-specified areas

Find places where the spec leaves ambiguous decisions that should have explicit design intent from the user. Examples:

  • A phase says "update the handler" but two handlers exist and the spec does not say which one
  • A schema change is described but the migration path for existing data on disk is not addressed
  • A new dependency is introduced between two modules but the spec does not state which module owns the interface
  • Error handling or edge cases are not mentioned for a path that can clearly fail
  • The spec describes behavior but does not specify what happens when the precondition is not met

Do not flag things that are obviously implied by context. Flag things where a reasonable implementer would have to guess.

Bugs

Find design-level logical errors — things that would send an implementer down the wrong path or produce incorrect behavior that tooling won't catch. Examples:

  • A phase deletes a module but a later phase depends on the concept it provided (not just the import — the typecheck catches that)
  • The spec contradicts its own goals or non-goals (e.g., says "calendar support later" but removes the only calendar mechanism without acknowledging it)
  • A fan-out loop creates sessions but nothing deduplicates if the same event matches the same trigger twice
  • The spec assumes a data shape or behavior that doesn't match reality in the codebase

Do not flag:

  • Missing imports/exports — the typechecker catches these
  • Exact function signatures or parameter mismatches — the implementer will resolve these during development
  • Test assertion details — the test runner catches these
  • Wiring specifics that are obvious from context (e.g., "this function isn't exported yet" — that's an implementation detail, not a spec concern)
Show full SKILL.md (274 more words)Show less
Adherence to spec requirements

Check whether the spec follows the structure and principles listed in this skill:

  • Does it have all required sections (problem overview, solution overview, goals, non-goals, important files, implementation)?
  • Is each phase commit-sized (under 100 lines of change)?
  • Does each phase have success criteria that verify the thing most likely to go wrong?
  • Does the spec avoid speccing extensibility, abstraction layers, or polish that nobody asked for?
  • Are there phases that are pure setup or refactoring with no user-facing progress?
  • Is the sanity checklist present and correct?
  • Does the spec represent the simplest version that works end-to-end?

Do not check whether guiding questions were asked — the reviewer does not have context about the conversation that produced the spec. Assume all decisions in the spec were intentional.

Step 4: Structure your response

Use this format:

markdown
# Spec Review: [spec title]

## Under-specified

- [Finding with spec section reference and source file reference]

## Bugs

- [Finding with spec section reference and source file reference]

## Adherence

- [Finding referencing specific requirement from this skill]

## Verdict

[2-3 sentences. State whether the spec is ready to implement, needs minor clarifications, or needs significant rework.]

If a category has no findings, write "None" under it.

Principles

  • Review the plan, not the implementation. A spec is a design document, not a line-by-line coding guide. Don't flag things that tooling (typechecker, linter, test runner) will catch during implementation. Focus on decisions that, if wrong, would waste significant time or produce incorrect behavior.
  • Be specific. Every finding must reference a spec section and a source file or requirement in this skill.
  • Be conservative. Only flag things that would cause an implementer to go down the wrong path, produce a design-level bug, or violate an explicit rule in this skill.
  • Do not suggest scope additions. The goal is to find holes in the existing scope, not to expand it.
  • Do not comment on writing style or formatting unless it violates the structure requirements in this skill.

© cashew-labs, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/spec-review of cashew-labs/libretto.

Open the folder on GitHubat commit 41ab782

Compare with similar skills

Spec Review next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Spec Review compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Spec Review this skillcashew-labs/libretto904—~1.2kAutomated safety check: PassMIT
Vercel Composition Patternssupabase/supabase111k58 repos~726Automated safety check: PassMIT
Finishing a Development Branchobra/superpowers297k5 repos~1.9kAutomated safety check: PassMIT
Typescript Advanced Typesrolling-scopes/rsschool-app10k25 repos~4.2kAutomated safety check: PassMPL-2.0
PR Babysitteropeninterpreter/openinterpreter69k3 repos~4.2kAutomated safety check: PassApache-2.0
Code Review ChecklistshareAI-lab/learn-claude-code78k4 repos~1.1kAutomated safety check: PassMIT

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Categories

Questions about Spec Review

What does Spec Review do?

Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill. Spec Review is an agent skill from cashew-labs/libretto. Review a spec for under-specified areas, bugs, and adherence to the spec requirements in this skill.

When should I use Spec Review?

Spec Review fits situations like: asked to review.

How do I install Spec Review in Claude Code?

Run `npx skills add cashew-labs/libretto --skill spec-review -a claude-code`. Or copy the skill folder (.agents/skills/spec-review in cashew-labs/libretto) into .claude/skills/spec-review in your project. Claude Code loads it when a task matches its description.

How do I install Spec Review in Codex?

Run `npx skills add cashew-labs/libretto --skill spec-review -a codex`. Or copy the skill folder (.agents/skills/spec-review in cashew-labs/libretto) into .agents/skills/spec-review in your project. Codex loads it when a task matches its description.

Can I use Spec Review in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add cashew-labs/libretto --skill spec-review -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/spec-review, .gemini/skills/spec-review, .github/skills/spec-review and .opencode/skills/spec-review in your project.

What does Spec Review need to run?

SKILL.md names no scripts, command-line tools or credentials: Spec Review is instructions for the agent only.

Does Spec Review access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Spec Review safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Spec Review use?

Spec Review is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Spec Review use?

About 1.2k tokens (SKILL.md is roughly 4.8k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Spec Review?

Skills that share tags, products or a category with Spec Review: Vercel Composition Patterns (supabase/supabase, 111k stars), Finishing a Development Branch (obra/superpowers, 297k stars), Typescript Advanced Types (rolling-scopes/rsschool-app, 10k stars) and PR Babysitter (openinterpreter/openinterpreter, 69k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Spec Review?

cashew-labs (a GitHub organization) maintains it in cashew-labs/libretto, which has 904 GitHub stars. The repository holds 21 skills in this directory. The repository was last updated on August 21, 2026.

Source: cashew-labs/libretto on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.