What is guide-swift-concurrency?

A practical guide to writing and reviewing Swift code that runs tasks at the same time, including actors, cancellation, and asynchronous data streams.

Use it when building, reviewing, or debugging Swift concurrency, moving from Grand Central Dispatch to Swift concurrency, or fixing strict-concurrency compiler diagnostics.

It helps prevent data races, incorrect cancellation, and other bugs that can occur when concurrent code runs in an unexpected order.

guide-swift-concurrency — Skill for Claude Code by Prisma-Labs-Dev

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add Prisma-Labs-Dev/apple-skills --skill guide-swift-concurrency

Clone the repo

git clone --depth 1 https://github.com/Prisma-Labs-Dev/apple-skills

Made for: Claude Code.

Or install apple-skills, the plugin that ships this one along with the rest of its 36 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency/github.svg)](https://agentmods.dev/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency)

Your own site

<a href="https://agentmods.dev/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency"><img src="https://agentmods.dev/badge/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency"><img src="https://agentmods.dev/badge/skills/prisma-labs-dev/apple-skills/guide-swift-concurrency.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 765 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00045	$0.00765
Opus 5	$0.00023	$0.00382
Sonnet 5	$0.00009	$0.00153
Haiku 4.5	$0.00005	$0.00076

Measured 10d ago against content hash bb277ea6f528, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

guide-swift-concurrency scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/guide-swift-concurrency/SKILL.md · 56 lines

How it starts

The opening of the file, as written. The whole thing — 56 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Guide Skill — This is an expert workflow/pattern guide, not API reference documentation. Originally from twostraws/Swift-Concurrency-Agent-Skill by Paul Hudson. MIT License.

Swift Concurrency Patterns

Review and write Swift concurrency code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems — do not nitpick or invent issues.

Core Instructions

Target Swift 6.2 or later with strict concurrency checking.
Prefer structured concurrency (task groups) over unstructured (Task {}).
Prefer Swift concurrency over GCD for new code. GCD is still acceptable in low-level code, framework interop, or performance-critical synchronous work.
Do not suggest @unchecked Sendable to fix compiler errors — prefer actors, value types, or sending parameters.

Review Process

Scan for known-dangerous patterns using references/hotspots.md.
Check for Swift 6.2 concurrency behavior using references/new-features.md.
Validate actor usage for reentrancy and isolation using references/actors.md.
Ensure structured concurrency is preferred using references/structured.md.
Check unstructured task usage using references/unstructured.md.
Verify cancellation handling using references/cancellation.md.
Validate async stream and continuation usage using references/async-streams.md.
Check bridging code between sync and async using references/bridging.md.
Review legacy concurrency migrations using references/interop.md.
Cross-check against common failure modes using references/bug-patterns.md.
If strict-concurrency errors exist, map diagnostics to fixes using references/diagnostics.md.
If reviewing tests, check async test patterns using references/testing.md.

If doing partial work, load only the relevant reference files.

References

Topic	Reference
Grep targets for code review — known-dangerous patterns	`references/hotspots.md`
Swift 6.2: default isolation, `@concurrent`, `Task.immediate`, isolated deinit	`references/new-features.md`
Actor reentrancy, global actor inference, isolation patterns	`references/actors.md`
Task groups, `async let`, `withDiscardingTaskGroup`, concurrency limits	`references/structured.md`
`Task` vs `Task.detached`, when `Task {}` is a code smell	`references/unstructured.md`
Cooperative cancellation, `withTaskCancellationHandler`, broken patterns	`references/cancellation.md`
`AsyncStream.makeStream(of:)`, continuation lifecycle, back-pressure	`references/async-streams.md`
Checked continuations, wrapping delegates, `@unchecked Sendable`	`references/bridging.md`
GCD migration, Combine to AsyncSequence, completion handlers, locks	`references/interop.md`
Common concurrency failure modes LLMs produce and their fixes	`references/bug-patterns.md`
Strict-concurrency compiler errors mapped to likely fixes	`references/diagnostics.md`
Async test patterns, race detection, avoiding timing-based tests	`references/testing.md`

Read the full file on GitHub · 56 lines

Files

What ships with it

12 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

10d ago First seen · 56 lines · 45 tokens per session scan A bb277ea6f528

Subscribe to this mod's changes

guide-swift-concurrency is a skill published in the GitHub repository Prisma-Labs-Dev/apple-skills (325 stars, last pushed 1mo ago), licensed MIT. It adds 45 tokens to every session and 765 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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