# Swift Concurrency Expert

Swift Concurrency review and remediation for Swift 6.2+.

- Repository: https://github.com/Dimillian/Skills (4021 stars)
- Category: Mobile
- License: MIT
- Last updated: 2026-03-29
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Dimillian/Skills --skill swift-concurrency-expert -g -a claude-code -y`
Codex: `npx skills add Dimillian/Skills --skill swift-concurrency-expert -g -a codex -y`
Cursor: `npx skills add Dimillian/Skills --skill swift-concurrency-expert -g -a cursor -y`
Gemini CLI: `npx skills add Dimillian/Skills --skill swift-concurrency-expert -g -a gemini-cli -y`

## Description

Swift Concurrency review and remediation for Swift 6.2+. Use when asked to review Swift Concurrency usage, improve concurrency compliance, or fix Swift concurrency compiler errors in a feature or file. Concrete actions include adding Sendable conformance, applying @MainActor annotations, resolving actor isolation warnings, fixing data race diagnostics, and migrating completion handlers to async/await.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Swift Concurrency Expert

## Overview

Review and fix Swift Concurrency issues in Swift 6.2+ codebases by applying actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes.

## Workflow

### 1. Triage the issue

- Capture the exact compiler diagnostics and the offending symbol(s).
- Check project concurrency settings: Swift language version (6.2+), strict concurrency level, and whether approachable concurrency (default actor isolation / main-actor-by-default) is enabled.
- Identify the current actor context (`@MainActor`, `actor`, `nonisolated`) and whether a default actor isolation mode is enabled.
- Confirm whether the code is UI-bound or intended to run off the main actor.

### 2. Apply the smallest safe fix

Prefer edits that preserve existing behavior while satisfying data-race safety.

Common fixes:
- **UI-bound types**: annotate the type or relevant members with `@MainActor`.
- **Protocol conformance on main actor types**: make the conformance isolated (e.g., `extension Foo: @MainActor SomeProtocol`).
- **Global/static state**: protect with `@MainActor` or move into an actor.
- **Background work**: move expensive work into a `@concurrent` async function on a `nonisolated` type or use an `actor` to guard mutable state.
- **Sendable errors**: prefer immutable/value types; add `Sendable` conformance only when correct; avoid `@unchecked Sendable` unless you can prove thread safety.

### 3. Verify the fix

- Rebuild and confirm all concurrency diagnostics are resolved with no new warnings introduced.
- Run the test suite to check for regressions, concurrency changes can introduce subtle runtime issues even when the build is clean.
- If the fix surfaces new warnings, treat each one as a fresh triage (return to step 1) and resolve iteratively until the build is clean and tests pass.

### Examples

**UI-bound type, adding `@MainActor`**

The rest: https://github.com/Dimillian/Skills/blob/HEAD/swift-concurrency-expert/SKILL.md