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Official agent skill

Review Pyrefly Diff

by facebook in facebook/pyrefly

Reviews a comma separated pyrefly diff according to the pyrefly review best practices.

OfficialMITAuto-check passedDevelopment

Install Review Pyrefly Diff

skills CLI
$ npx skills add facebook/pyrefly --skill review-pyrefly-diff -a claude-code

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

GitHub CLI
$ gh skill install facebook/pyrefly review-pyrefly-diff --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/facebook/pyrefly.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/review-pyrefly-diff .claude/skills/review-pyrefly-diff && 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
review-pyrefly-diff
GitHub stars
7.1k
Token cost
~863 tokens
SKILL.md length
435 words
Files
1
Skills in repo
6
Repo updated
First seen
Licence
MIT

At a glance

Reviews a comma separated pyrefly diff according to the pyrefly review best practices.

  • Development work in your project
  • SKILL.md covers Review Focus Areas, Pyrefly-Specific Guidelines and Output Format
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Review Pyrefly Diff is an agent skill from facebook/pyrefly, published by the product's own GitHub organization. Reviews a comma separated pyrefly diff according to the pyrefly review best practices.

Its SKILL.md is about 860 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. It works with Rust and Python. The repository describes itself as: A fast type checker and language server for Python. The licence is MIT.

When your agent uses it

  • Development work in your project

Example prompts

  • “Use the review-pyrefly-diff skill to review a comma separated pyrefly diff according to the pyrefly review best practices”
  • “/review-pyrefly-diff”

Requirements

  • Python 3

What it can do on your machine

Read from SKILL.md and the folder at commit 0e44796. 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.

    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

Review Pyrefly Diff loads about 863 tokens when it runs. Until then it costs about 27 tokens; SKILL.md has 435 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~27
When it runs · the whole SKILL.md, loaded when a task matches
~863

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 facebook/pyrefly at commit 0e44796, republished under its MIT licence (© facebook). 435 words, ~863 tokens.

Download SKILL.mdSave it as .claude/skills/review-pyrefly-diff/SKILL.md (or your agent's skills folder).
name
review-pyrefly-diff
description
Reviews a comma separated pyrefly diff according to the pyrefly review best practices.

This skill is intended to be used by interal Meta employees to review code changes in phabricator. This should not be used to review Github pull requests.

You will take in a comma separated list of Phabricator Diff numbers and review them according to the pyrefly review best practices. For each diff that is passed in, use a new subagent to perform the review in parallel.

Code Review Guidelines for Pyrefly

You are reviewing a Phabricator Diff for Pyrefly, a fast language server and type checker for Python written in Rust.

Review Focus Areas

Correctness
  • Logic errors and edge cases
  • Null/None/Option handling
  • Off-by-one errors
  • Resource leaks or missing cleanup
  • Incorrect error handling
Security
  • Input validation issues
  • Injection risks (command injection, path traversal)
  • Unsafe deserialization
  • Authentication/authorization gaps
Performance
  • N+1 patterns or unnecessary iterations
  • Excessive allocations or cloning
  • Blocking operations in async contexts
  • Missing caching opportunities for expensive operations
Testing
  • Missing test coverage for new functionality
  • Edge cases not covered by tests
  • Flaky test patterns
  • Internal CI does not provide Windows coverage. Check filesystem and text-fixture tests for assumptions that differ on Windows, especially line endings, path separators, case sensitivity, symlinks, executable permissions, and temporary-file behavior. Prefer matching semantic content without consuming host-specific separators or line endings.
Style and Consistency
  • Naming conventions (Rust: snake_case for functions, CamelCase for types)
  • Consistency with existing codebase patterns
  • Unnecessary complexity or over-engineering
  • Check for missed opportunities for code reuse
Architecture
  • Separation of concerns
  • Tight coupling between components
  • Breaking changes to public APIs

Pyrefly-Specific Guidelines

Show full SKILL.md (187 more words)Show less
Rust Conventions
  • Prefer impl Trait over dyn Trait where possible
  • Use ? for error propagation instead of manual matching
  • Avoid .unwrap() in production code; prefer .expect() with context or proper error handling
  • Check for existing helpers in the pyrefly_types crate before manually creating or destructuring a Type
Type Checker Concerns
  • Changes to type inference should consider edge cases
  • Modifications to error messages should be clear and actionable
  • Performance is critical for the language server
Code Style
  • Keep It Simple Stupid (KISS) - minimize concept count
  • Don't Repeat Yourself (DRY) - but don't over-abstract
  • Comments should explain "why", not "what"
  • Minimize places where Expr nodes are passed around

Output Format

Provide your review in the following structure:

Summary

A brief (2-3 sentence) overview of what this diff does and your overall assessment.

Issues Found

List any problems, organized by severity:

  • Critical: Must fix before landing (correctness, security)
  • Major: Should fix (performance, maintainability)
  • Minor: Nice to fix (style, documentation)

For each issue, include:

  • File and line reference
  • Description of the problem
  • Suggested fix (if applicable)
Positive Observations

Note any particularly well-done aspects of the code.

Questions

Any clarifying questions for the author.

© facebook, 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/review-pyrefly-diff of facebook/pyrefly.

Open the folder on GitHubat commit 0e44796

Compare with similar skills

Review Pyrefly Diff 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.

Review Pyrefly Diff compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Review Pyrefly Diff this skillfacebook/pyrefly7.1k—~863Automated safety check: PassMIT
Apple Container Test RunnerRustPython/RustPython22k—~467Automated safety check: PassMIT
Release Skillsnexmoe/eve4213 repos~3.3kAutomated safety check: PassNone
RustPython C-API ExpansionRustPython/RustPython22k—~831Automated safety check: PassMIT
jscpd Code Migration Trackerkucherenko/jscpd6.3k—~5kAutomated safety check: PassMIT
RustPython Stdlib UpgradeRustPython/RustPython22k—~876Automated safety check: PassMIT

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More from facebook/pyrefly

  • Add Torch Shapes Example

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    A skill your agent uses when adding a new PyTorch model to Pyrefly's shape-tracking example corpus under tensor-shapes/pyrefly-torch-stubs/examples — i.e.

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  • Benchmark Pyrefly

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    7.1k GitHub stars~1.8k tokensUpdated today
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  • Modify Shaped Array Dsl

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    A skill your agent uses when Pyrefly computes a wrong tensor shape (or is missing one that can't be expressed in a stub signature) and you need to add or fix a shape-DSL rule.

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  • Add Shape Types To Torch Model

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    Port a PyTorch model to use pyrefly's tensor shape type system (Tensor[[B, C, H, W]], Int[T]).

    7.1k GitHub stars~13k tokensUpdated today
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  • Score Pyrefly Change

    facebook/pyrefly

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    Produces a scorecard evaluating a pyrefly change on correctness and quality.

    7.1k GitHub stars~1.5k tokensUpdated today
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Works with

Categories

Questions about Review Pyrefly Diff

What does Review Pyrefly Diff do?

Reviews a comma separated pyrefly diff according to the pyrefly review best practices. Review Pyrefly Diff is an agent skill from facebook/pyrefly, published by the product's own GitHub organization. Reviews a comma separated pyrefly diff according to the pyrefly review best practices.

When should I use Review Pyrefly Diff?

Review Pyrefly Diff fits situations like: development work in your project.

How do I install Review Pyrefly Diff in Claude Code?

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

How do I install Review Pyrefly Diff in Codex?

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

Can I use Review Pyrefly Diff 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 facebook/pyrefly --skill review-pyrefly-diff -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/review-pyrefly-diff, .gemini/skills/review-pyrefly-diff, .github/skills/review-pyrefly-diff and .opencode/skills/review-pyrefly-diff in your project.

What does Review Pyrefly Diff need to run?

SKILL.md names no scripts, command-line tools or credentials: Review Pyrefly Diff is instructions for the agent only. Our summary lists: Python 3.

Does Review Pyrefly Diff 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 Review Pyrefly Diff 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 Review Pyrefly Diff use?

Review Pyrefly Diff 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 Review Pyrefly Diff use?

About 863 tokens (SKILL.md is roughly 3.5k 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 Review Pyrefly Diff?

Skills that share tags, products or a category with Review Pyrefly Diff: Apple Container Test Runner (RustPython/RustPython, 22k stars), Release Skills (nexmoe/eve, 421 stars), RustPython C-API Expansion (RustPython/RustPython, 22k stars) and jscpd Code Migration Tracker (kucherenko/jscpd, 6.3k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Review Pyrefly Diff?

facebook (a GitHub organization, an official publisher) maintains it in facebook/pyrefly, which has 7,051 GitHub stars. The repository holds 6 skills in this directory. The repository was last updated on October 7, 2026.

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