New: 98,000+ skills indexed from GitHub repos with 100+ stars · every skill safety-checkedBrowse top skillsTop skills
Esc to closeBrowse all skills
Submit a skillBrowse skills
Submit a skillBrowse skills

Agent skill

Swift Concurrency

by henrypldev in henrypldev/react-native-nitro-mlx

Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or…

MITAuto-check passedDevelopment

Install Swift Concurrency

skills CLI
$ npx skills add henrypldev/react-native-nitro-mlx --skill swift-concurrency -a claude-code

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

GitHub CLI
$ gh skill install henrypldev/react-native-nitro-mlx swift-concurrency --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/henrypldev/react-native-nitro-mlx.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/swift-concurrency .claude/skills/swift-concurrency && 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
swift-concurrency
GitHub stars
100
Used in
3 other repos
Token cost
~3.1k tokens
SKILL.md length
1,351 words
Files
16 (incl. references)
Skills in repo
1
Repo updated
First seen
Licence
MIT

At a glance

Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or…

  • Works in 4 steps: Analyze Package.swift or .pbxproj to… → Capture the exact diagnostic and… → Determine the isolation boundary:… → …
  • Tasks that involve Async programming
  • SKILL.md covers Fast Path, Quick Fix Mode, Common Diagnostics and When Quick Fixes Fail, plus 6 more sections
  • Calls swift

What it does

Swift Concurrency is an agent skill from henrypldev/react-native-nitro-mlx. Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or concurrency-related compiler and linter warnings.

Its SKILL.md is about 3.1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 16 other files, including reference files (for example `references/_index.md`, `references/actors.md` and `references/async-algorithms.md`).

It sits in Development, covering Async programming, Linting and formatting and iOS development. It works with Swift and Xcode. The repository describes itself as: Run LLMs on device using Apple's MLX. The licence is MIT.

When your agent uses it

  • Tasks that involve Async programming
  • Tasks that involve Linting and formatting
  • Tasks that involve iOS development

Example prompts

  • “/swift-concurrency”

Workflow steps

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

  1. Analyze Package.swift or .pbxproj to determine Swift language mode, strict concurrency level, default isolation, and upcoming features. Do…
  2. Capture the exact diagnostic and offending symbol.
  3. Determine the isolation boundary: @MainActor, custom actor, actor instance isolation, or nonisolated.
  4. Confirm whether the code is UI-bound or intended to run off the main actor. When spawning unstructured tasks, inspect the synchronous…

What it can do on your machine

Read from SKILL.md and the folder at commit d58dda0. 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

    Shell commands in SKILL.md call:

    • swift

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

  • Network

    Links to these hosts (documentation or services it may open):

    • swiftconcurrencycourse.com

    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 loads about 3.1k tokens when it runs, and up to ~57k if it reads all its reference files. Until then it costs about 65 tokens; SKILL.md has 1,351 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~65
When it runs · the whole SKILL.md, loaded when a task matches
~3.1k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~57k

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 henrypldev/react-native-nitro-mlx at commit d58dda0, republished under its MIT licence (© henrypldev). 1,351 words, ~3,118 tokens.

Download SKILL.mdSave it as .claude/skills/swift-concurrency/SKILL.md (or your agent's skills folder). This skill also uses 15 other files; get the full folder from GitHub.
name
swift-concurrency
description
Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or concurrency-related compiler and linter warnings.

Swift Concurrency

Fast Path

Before proposing a fix:

  1. Analyze Package.swift or .pbxproj to determine Swift language mode, strict concurrency level, default isolation, and upcoming features. Do this always, not only for migration work.
  2. Capture the exact diagnostic and offending symbol.
  3. Determine the isolation boundary: @MainActor, custom actor, actor instance isolation, or nonisolated.
  4. Confirm whether the code is UI-bound or intended to run off the main actor. When spawning unstructured tasks, inspect the synchronous prefix (everything before the first await): start on @MainActor only when that prefix truly needs main-actor access; otherwise use Task { @concurrent in ... } and hop back with MainActor.run only after the suspension. A trivial non-main line (for example, print) followed by main-actor work in the same prefix is not a reason to use @concurrent. For delayed retries, timers, and backoff tasks, separate the waiting from the UI mutation. The sleep often belongs off the main actor even when the final state update belongs on it.

Project settings that change concurrency behavior:

SettingSwiftPM (Package.swift)Xcode (.pbxproj)
Language modeswiftLanguageVersions or -swift-version (// swift-tools-version: is not a reliable proxy)Swift Language Version
Strict concurrency.enableExperimentalFeature("StrictConcurrency=targeted")SWIFT_STRICT_CONCURRENCY
Default isolation.defaultIsolation(MainActor.self)SWIFT_DEFAULT_ACTOR_ISOLATION
Upcoming features.enableUpcomingFeature("NonisolatedNonsendingByDefault")SWIFT_UPCOMING_FEATURE_*
Approachable ConcurrencyN/A (use individual upcoming features)SWIFT_APPROACHABLE_CONCURRENCY

Xcode 26 note: New projects created in Xcode 26 will often start with SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor and SWIFT_APPROACHABLE_CONCURRENCY = YES enabled by default. Treat these as likely defaults for newly created projects, not as confirmed settings.

If any of these are unknown, ask the developer to confirm them before giving migration-sensitive guidance. Do not guess, even for new Xcode 26 projects.

Guardrails:

  • Do not recommend @MainActor as a blanket fix. Justify why the code is truly UI-bound.
  • Prefer structured concurrency over unstructured tasks. Use Task.detached only with a clear reason.
  • If recommending @preconcurrency, @unchecked Sendable, or nonisolated(unsafe), require a documented safety invariant and a follow-up removal plan.
  • Optimize for the smallest safe change. Do not refactor unrelated architecture during migration.
  • Course references are for deeper learning only. Use them sparingly and only when they clearly help answer the developer's question.

Quick Fix Mode

Use Quick Fix Mode when all of these are true:

  • The issue is localized to one file or one type.
  • The isolation boundary is clear.
  • The fix can be explained in 1-2 behavior-preserving steps.

Skip Quick Fix Mode when any of these are true:

  • Build settings or default isolation are unknown.
  • The issue crosses module boundaries or changes public API behavior.
  • The likely fix depends on unsafe escape hatches.

Common Diagnostics

DiagnosticFirst checkSmallest safe fixEscalate to
Main actor-isolated ... cannot be used from a nonisolated contextIs this truly UI-bound?Isolate the caller to @MainActor or use await MainActor.run { ... } only when main-actor ownership is correct.references/actors.md, references/threading.md
Actor-isolated type does not conform to protocolMust the requirement run on the actor?Prefer isolated conformance (e.g., extension Foo: @MainActor SomeProtocol); use nonisolated only for truly nonisolated requirements.references/actors.md
Sending value of non-Sendable type ... risks causing data racesWhat isolation boundary is being crossed?Keep access inside one actor, or convert the transferred value to an immutable/value type.references/sendable.md, references/threading.md
SwiftLint async_without_awaitIs async actually required by protocol, override, or @concurrent?Remove async, or use a narrow suppression with rationale. Never add fake awaits.references/linting.md
wait(...) is unavailable from asynchronous contextsIs this legacy XCTest async waiting?Replace with await fulfillment(of:) or Swift Testing equivalents.references/testing.md
Core Data concurrency warningsAre NSManagedObject instances crossing contexts or actors?Pass NSManagedObjectID or map to a Sendable value type.references/core-data.md
Thread.current unavailable from asynchronous contextsAre you debugging by thread instead of isolation?Reason in terms of isolation and use Instruments/debugger instead.references/threading.md
SwiftLint concurrency-related warningsWhich specific lint rule triggered?Use references/linting.md for rule intent and preferred fixes; avoid dummy awaits.references/linting.md
... cannot satisfy conformance requirement for a 'Sendable' type parameter (SendableMetatype)Does the conformance carry global-actor isolation?Remove actor isolation from the conformance, or avoid passing the metatype across isolation boundaries. See SendableMetatype section in references/actors.md.references/actors.md

When Quick Fixes Fail

  1. Gather project settings if not already confirmed.
  2. Re-evaluate which isolation boundaries the type crosses.
  3. Route to the matching reference file for a deeper fix.
  4. If the fix may change behavior, document the invariant and add verification steps.

Smallest Safe Fixes

Prefer changes that preserve behavior while satisfying data-race safety:

  • UI-bound state: isolate the type or member to @MainActor.
  • Shared mutable state: move it behind an actor, or use @MainActor only if the state is UI-owned.
  • Background work: when work must hop off caller isolation, use an async API marked @concurrent; when work can safely inherit caller isolation, use nonisolated without @concurrent. When spawning a Task, match entry isolation to its synchronous prefix. If nothing before the first await needs the main actor, use Task { @concurrent in ... } and hop back via await MainActor.run { ... } for the UI update. If the prefix mixes a trivial non-main statement with main-actor work, keep the inherited @MainActor start—splitting the cheap line off-main is not worth an extra hop.
  • Sendability issues: prefer immutable values and explicit boundaries over @unchecked Sendable.
Show full SKILL.md (507 more words)Show less

Concurrency Tool Selection

NeedToolKey Guidance
Single async operationasync/awaitDefault choice for sequential async work
Fixed parallel operationsasync letKnown count at compile time; auto-cancelled on throw
Dynamic parallel operationswithTaskGroupUnknown count; structured — cancels children on scope exit
Sync → async bridgeTask { }Inherits actor context; use Task.detached only with documented reason
Shared mutable stateactorPrefer over locks/queues; keep isolated sections small
UI-bound state@MainActorOnly for truly UI-related code; justify isolation
Common Scenarios

Network request with UI update

swift
Task { @concurrent in
    let data = try await fetchData()
    await MainActor.run { self.updateUI(with: data) }
}

Processing array items in parallel

swift
await withTaskGroup(of: ProcessedItem.self) { group in
    for item in items {
        group.addTask { await process(item) }
    }
    for await result in group {
        results.append(result)
    }
}

Task entry isolation

Match a Task's entry isolation to its synchronous prefix (everything from { to the first await).

  • If anything in that prefix needs @MainActor, keep the inherited @MainActor start.
  • If nothing in that prefix needs @MainActor, prefer Task { @concurrent in ... } and hop back only for UI-owned mutation.
swift
// ❌ Synchronous prefix is empty; first work hops away
Task {
    await hopToOtherIsolationDomain()
}

// ❌ Synchronous prefix is only `print` (trivial, non-main); first await hops away
Task {
    print("Also not main-thread-bound")
    await hopToOtherIsolationDomain()
}

// ✅ Start off the main actor, hop back only for UI work
Task { @concurrent in
    await hopToOtherIsolationDomain()
    await MainActor.run { updateUI() }
}

// ✅ Synchronous prefix DOES contain main-actor work — keep inheritance
Task {
    print("debug")              // trivial, non-main — rides along
    self.isLoading = true       // needs @MainActor, before any await
    await fetchData()
}

Swift 6 Migration Quick Guide

Key changes in Swift 6:

  • Strict concurrency checking enabled by default
  • Complete data-race safety at compile time
  • Sendable requirements enforced on boundaries
  • Isolation checking for all async boundaries
Migration Validation Loop

Apply this cycle for each migration change:

  1. Build — Run swift build or Xcode build to surface new diagnostics
  2. Fix — Address one category of error at a time (e.g., all Sendable issues first)
  3. Rebuild — Confirm the fix compiles cleanly before moving on
  4. Test — Run the test suite to catch regressions (swift test or Cmd+U)
  5. Only proceed to the next file/module when all diagnostics are resolved

If a fix introduces new warnings, resolve them before continuing. Never batch multiple unrelated fixes — keep commits small and reviewable.

For detailed migration steps, see references/migration.md.

Reference Router

Open the smallest reference that matches the question:

  • Foundations
    • references/async-await-basics.md — async/await syntax, execution order, async let, URLSession patterns
    • references/tasks.md — Task lifecycle, cancellation, priorities, task groups, structured vs unstructured
    • references/actors.md — Actor isolation, @MainActor, global actors, reentrancy, custom executors, Mutex
    • references/sendable.md — Sendable conformance, value/reference types, @unchecked, region isolation
    • references/threading.md — Execution model, suspension points, Swift 6.2 isolation behavior
  • Streams
    • references/async-sequences.md — AsyncSequence, AsyncStream, when to use vs regular async methods
    • references/async-algorithms.md — Debounce, throttle, merge, combineLatest, channels, timers
  • Applied topics
    • references/testing.md — Swift Testing first, XCTest fallback, leak checks
    • references/performance.md — Profiling with Instruments, reducing suspension points, execution strategies
    • references/memory-management.md — Retain cycles in tasks, memory safety patterns
    • references/core-data.md — NSManagedObject sendability, custom executors, isolation conflicts
  • Migration and tooling
    • references/migration.md — Swift 6 migration strategy, closure-to-async conversion, @preconcurrency, FRP migration
    • references/linting.md — Concurrency-focused lint rules and SwiftLint async_without_await
  • Glossary
    • references/glossary.md — Quick definitions of core concurrency terms

Verification Checklist

When changing concurrency code:

  1. Re-check build settings before interpreting diagnostics.
  2. Build and clear one category of errors before moving on. Do not batch unrelated fixes into the same change.
  3. Run tests, especially actor-, lifetime-, and cancellation-sensitive tests.
  4. Use Instruments for performance claims instead of guessing.
  5. Verify deallocation and cancellation behavior for long-lived tasks.
  6. Check Task.isCancelled in long-running operations.
  7. Never use semaphores or ad hoc locking in async contexts when actor isolation or Mutex would express ownership more safely.

Note: This skill is based on the comprehensive Swift Concurrency Course by Antoine van der Lee.

© henrypldev, 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 15 other files (references) in .agents/skills/swift-concurrency of henrypldev/react-native-nitro-mlx.

  • SKILL.md
  • references/_index.md
  • references/actors.md
  • references/async-algorithms.md
  • references/async-await-basics.md
  • references/async-sequences.md
  • references/core-data.md
  • references/glossary.md
  • references/linting.md
  • references/memory-management.md
  • references/migration.md
  • references/performance.md
  • references/sendable.md
  • references/tasks.md
  • references/testing.md
  • references/threading.md

Open the folder on GitHubat commit d58dda0

Used in 3 other repositories

We found 4 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 3 other GitHub owners. This page covers the copy in henrypldev/react-native-nitro-mlx, which our catalogue first saw on October 7, 2026.

Compare with similar skills

Swift Concurrency 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.

Swift Concurrency compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Swift Concurrency this skillhenrypldev/react-native-nitro-mlx1003 repos~3.1kAutomated safety check: PassMIT
Swift Concurrencynimblehq/ios-templates110—~1.7kAutomated safety check: PassMIT
Swift Concurrencyjamesrochabrun/skills216—~1.9kAutomated safety check: PassMIT
Concurrency Patternsgustavscirulis/snapgrid1171 repos~1.2kAutomated safety check: PassCustom licence
Swift Concurrency Protwostraws/Swift-Concurrency-Agent-Skill564—~1.4kAutomated safety check: PassMIT
Swift Concurrencysupabitapp/supaterm172—~3.3kAutomated safety check: PassCustom licence

Similar skills

  • Swift Concurrency

    nimblehq/ios-templates

    Write, review, or fix Swift 6 concurrency code using actors, Sendable, structured concurrency, and the strict data-race-safety model.

    110 GitHub stars~1.7k tokensUpdated 2 mo ago
    DevelopmentAuto-check passed

  • Swift Concurrency

    jamesrochabrun/skills

    Guide for building, auditing, and refactoring Swift code using modern concurrency patterns (Swift 6+).

    216 GitHub stars~1.9k tokensUpdated 8 mo ago
    DevelopmentAuto-check passed

  • Concurrency Patterns

    gustavscirulis/snapgrid

    Swift concurrency patterns including Swift 6.2 approachable concurrency, structured concurrency, actors, continuations, and migration.

    117 GitHub starsUsed in 1 repo~1.2k tokens
    DevelopmentAuto-check passed

  • Swift Concurrency Pro

    twostraws/Swift-Concurrency-Agent-Skill

    Reviews Swift code for concurrency correctness, modern API usage, and common async/await pitfalls.

    564 GitHub stars~1.4k tokensUpdated 4 mo ago
    MobileAuto-check passed

  • Swift Concurrency

    supabitapp/supaterm

    Diagnose data races, convert callback-based code to async/await, implement actor isolation patterns, resolve Sendable conformance issues, and guide Swift 6 migration.

    172 GitHub stars~3.3k tokensUpdated 15 days ago
    DevelopmentAuto-check passed

  • Swift Concurrency

    AFK-surf/OpenBridge

    Expert guidance on Swift Concurrency best practices, patterns, and implementation.

    430 GitHub stars~2.8k tokensUpdated 4 mo ago
    DevelopmentAuto-check passed

Works with

Categories

Questions about Swift Concurrency

What does Swift Concurrency do?

Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or…. Swift Concurrency is an agent skill from henrypldev/react-native-nitro-mlx. Diagnose Swift Concurrency issues, refactor callback-based code to async/await, and guide Swift 6 migration when working with tasks, actors, @MainActor, Sendable, data races, thread safety, or concurrency-related compiler and linter warnings.

When should I use Swift Concurrency?

Swift Concurrency fits situations like: tasks that involve Async programming; tasks that involve Linting and formatting; tasks that involve iOS development.

How do I install Swift Concurrency in Claude Code?

Run `npx skills add henrypldev/react-native-nitro-mlx --skill swift-concurrency -a claude-code`. Or copy the skill folder (.agents/skills/swift-concurrency in henrypldev/react-native-nitro-mlx) into .claude/skills/swift-concurrency in your project. Claude Code loads it when a task matches its description.

How do I install Swift Concurrency in Codex?

Run `npx skills add henrypldev/react-native-nitro-mlx --skill swift-concurrency -a codex`. Or copy the skill folder (.agents/skills/swift-concurrency in henrypldev/react-native-nitro-mlx) into .agents/skills/swift-concurrency in your project. Codex loads it when a task matches its description.

Can I use Swift Concurrency 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 henrypldev/react-native-nitro-mlx --skill swift-concurrency -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/swift-concurrency, .gemini/skills/swift-concurrency, .github/skills/swift-concurrency and .opencode/skills/swift-concurrency in your project.

What does Swift Concurrency need to run?

Going by SKILL.md and its folder, Swift Concurrency needs the command-line tools its instructions call (swift).

Does Swift Concurrency access the network?

SKILL.md names 1 domain. As links in the text: swiftconcurrencycourse.com. This is read from the text; nothing was executed.

Is Swift Concurrency 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 Swift Concurrency use?

Swift Concurrency 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 Swift Concurrency use?

About 3.1k tokens (SKILL.md is roughly 12k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 54k tokens, read only when the agent opens those files.

What are the alternatives to Swift Concurrency?

Skills that share tags, products or a category with Swift Concurrency: Swift Concurrency (nimblehq/ios-templates, 110 stars), Swift Concurrency (jamesrochabrun/skills, 216 stars), Concurrency Patterns (gustavscirulis/snapgrid, 117 stars) and Swift Concurrency Pro (twostraws/Swift-Concurrency-Agent-Skill, 564 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Swift Concurrency?

henrypldev (a GitHub organization) maintains it in henrypldev/react-native-nitro-mlx, which has 100 GitHub stars. The repository was last updated on August 25, 2026.

Source: henrypldev/react-native-nitro-mlx on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.