Swift Concurrency Pro

What it does

When your agent uses it

• Reviewing Swift concurrency code
• Tasks that involve Async programming
• Tasks that involve iOS development

Example prompts

• “Use the swift-concurrency-pro skill to review Swift code for concurrency correctness, modern API usage, and common async/await pitfalls”
• “/swift-concurrency-pro”

Workflow steps

12 steps, taken from the first numbered list in SKILL.md.

1. 1Scan for known-dangerous patterns using references/hotspots.md to prioritize what to inspect.
2. 2Check for recent Swift 6.2 concurrency behavior using references/new-features.md.
3. 3Validate actor usage for reentrancy and isolation correctness using references/actors.md.
4. 4Ensure structured concurrency is preferred over unstructured where appropriate using references/structured.md.
5. 5Check unstructured task usage for correctness using references/unstructured.md.
6. 6Verify cancellation is handled correctly using references/cancellation.md.
7. 7Validate async stream and continuation usage using references/async-streams.md.
8. 8Check bridging code between sync and async worlds using references/bridging.md.
9. 9Review any legacy concurrency migrations using references/interop.md.
10. 10Cross-check against common failure modes using references/bug-patterns.md.
11. 11If the project has strict-concurrency errors, map diagnostics to fixes using references/diagnostics.md.
12. 12If reviewing tests, check async test patterns using references/testing.md.

What it can do on your machine

Read from SKILL.md and the folder at commit bee3f69. 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 swift).

  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

Swift Concurrency Pro loads about 1.4k tokens when it runs, and up to ~14k if it reads all its reference files. Until then it costs about 46 tokens; SKILL.md has 528 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~46

When it runs · the whole SKILL.md, loaded when a task matches

~1.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~14k

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

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 twostraws/Swift-Concurrency-Agent-Skill at commit bee3f69, republished under its MIT licence (© twostraws). 528 words, ~1,373 tokens.

name

swift-concurrency-pro

description

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

license

MIT

metadata.author

Paul Hudson

metadata.version

1.0

// Before
actor Cache {
    var items: [String: Data] = [:]

    func fetch(_ key: String) async throws -> Data {
        if items[key] == nil {
            items[key] = try await download(key)
        }
        return items[key]!
    }
}

// After
actor Cache {
    var items: [String: Data] = [:]

    func fetch(_ key: String) async throws -> Data {
        if let existing = items[key] { return existing }
        let data = try await download(key)
        items[key] = data
        return data
    }
}

// Before
for url in urls {
    Task { try await fetch(url) }
}

// After
try await withThrowingTaskGroup(of: Data.self) { group in
    for url in urls {
        group.addTask { try await fetch(url) }
    }

    for try await result in group {
        process(result)
    }
}

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

Files

SKILL.md and 17 other files (references, assets) in swift-concurrency-pro of twostraws/Swift-Concurrency-Agent-Skill.

• SKILL.md
• .claude-plugin/plugin.json
• agents/openai.yaml
• assets/swift-concurrency-pro-icon.png
• assets/swift-concurrency-pro-icon.svg
• references/actors.md
• references/async-streams.md
• references/bridging.md
• references/bug-patterns.md
• references/cancellation.md
• references/diagnostics.md
• references/hotspots.md
• references/interop.md
• references/new-features.md
• references/structured.md
• references/testing.md
• references/unstructured.md
• … and 1 more

Open the folder on GitHubat commit bee3f69