Swift Concurrency Pro (Paul Hudson): a Claude skill that reviews Swift code for async/await, actor and Sendable mistakes

Swift Concurrency Pro makes Claude review Swift code for concurrency mistakes like actor reentrancy, loose tasks and broken cancellation.

Installs: 12.3K; on skills.sh
Stars: 578; on GitHub
Files: 16; besides SKILL.md
Updated: May 2026; last repo commit

Ask Claude to review a Swift project and this skill walks it through a fixed 12-step checklist. It starts with dangerous patterns to search for, then checks Swift 6.2 changes, actors, task groups, loose tasks, cancellation, async streams, bridging, legacy GCD code, compiler diagnostics and tests. Each step has its own reference file, and a partial review loads only the files it needs.

Claude reports only real problems, grouped by file, with the line, the rule broken and a short before and after fix. It ends with a ranked summary. The skill aims at Swift 6.2 with strict concurrency checking, prefers async/await and task groups over GCD and loose tasks, and never suggests @unchecked Sendable as a quick fix. It bundles no scripts.

Good for

iOS and macOS developers moving a project to Swift 6 strict concurrency
Developers who want AI-written Swift concurrency code checked before merge
Teams migrating from GCD, completion handlers or Combine to async/await

Install swift-concurrency-pro

Claude Code

Copy this prompt.

Install the swift-concurrency-pro skill in Claude Code. Run this command:

/plugin marketplace add twostraws/Swift-Concurrency-Agent-Skill
/plugin install swift-concurrency-pro@swift-concurrency-agent-skill

Then check that it loaded and tell me how to use it.

2
Paste it into Claude Code. It shows the change and asks before running it.

Pick one route, not both. The plugin contains only this skill, and its manifest lists no hooks or MCP servers. The README triggers the skill with /swift-concurrency-pro.

From the project README. Source.

What's in the skill

When it loads

Reviews Swift code for concurrency correctness, modern API usage, and common async/await pitfalls. Use when reading, writing, or reviewing Swift concurrency code.

Sections in SKILL.md

Core Instructions
Output Format
DataLoader.swift
Summary
References

Key facts

Author: Paul Hudson (twostraws)
Repo: twostraws/swift-concurrency-agent-skill (swift-concurrency-pro)
License: MIT
Installs on skills.sh: 12,346 as of 2026-11-02
GitHub stars: 578 (whole repo) as of 2026-11-02
Last repo commit: 2026-05-17
Folder contents: 17 files in the skill folder: SKILL.md, 12 reference files, plugin.json, agents/openai.yaml and 2 icon files
skills.sh audits: Gen Agent Trust Hub pass, Socket pass, Snyk pass

What it includes

Searches for known dangerous patterns first, to focus the review.
Hotspot scan
Checks default actor isolation, @concurrent, Task.immediate and task naming.
Swift 6.2 changes
Checks reentrancy, shared-state annotations and isolation.
Actors
Prefers task groups over loops of loose Task {} calls.
Structured concurrency
Checks Task versus Task.detached and flags Task {} as a smell.
Unstructured tasks
Checks propagation and cooperative cancellation checks.
Cancellation
Checks stream factories, continuation lifecycle and back-pressure.
Async streams
Checks checked continuations and wrappers around old APIs.
Bridging
Covers moving from GCD, locks, completion handlers, delegates and Combine.
Legacy migration
Cross-checks common concurrency failure modes and their fixes.
Bug patterns
Maps strict-concurrency errors to likely fixes.
Compiler diagnostics
Reviews Swift Testing patterns and race detection, and avoids timing-based tests.
Async tests

From the official docs

Questions

What does Swift Concurrency Pro do?

It makes Claude review Swift code for concurrency correctness and modern API use. It follows 12 steps and reports only genuine problems, with a before and after fix for each. It covers actors, task groups, cancellation, async streams, bridging code, GCD migration, compiler diagnostics and tests.

How do I install it in Claude Code?

Use the plugin route in the install box. Add the twostraws marketplace, then install the swift-concurrency-pro plugin. The plugin holds this one skill, plus a manifest that points to the skill folder. The skills CLI command is the other route.

How do I run it?

The README says to type /swift-concurrency-pro in Claude Code or $swift-concurrency-pro in Codex. You can add instructions for a partial review, or ask in plain words to "use the Swift Concurrency Pro skill" on your project.

Does it work in Codex, Cursor or Gemini?

The README lists Claude Code, Codex, Cursor and Gemini. For anything but Claude Code, use the skills CLI command in the install box and pick the agent when it asks.

Does it need an API key or any tools?

No key or tool is mentioned. It bundles no scripts. It is a checklist with 12 reference files that Claude reads while reviewing your code.

Is it safe?

It bundles no scripts. It tells Claude to review code and report findings, and to ask before adding any third-party concurrency framework. Claude still reads your project files to do the review, so use it on code you are happy to share with your AI tool.

Which Swift version does it assume?

SKILL.md targets Swift 6.2 or later with strict concurrency checking. It also tells Claude to compare concurrency build settings when code spans several targets or packages.

How is it different from the other twostraws skills?

The README links separate skills for SwiftUI, SwiftData and Swift Testing from the same author. This one covers only concurrency.

Information

updated Nov 2, 2026

Repository: twostraws/swift-concurrency-agent-skill
Folder: swift-concurrency-pro

twostraws/swift-concurrency-agent-skill skills.sh

Sources

Docs, issue trackers and discussions this page is built from.

Show all 3

Swift Concurrency Agent Skill README · github.com
swift-concurrency-pro SKILL.md · github.com
swift-concurrency-pro on skills.sh · skills.sh