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.
npx skills add markdavidgan/apple-dev-skills --skill swift6-concurrencygit clone --depth 1 https://github.com/markdavidgan/apple-dev-skillsWrote 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.
[](https://agentmods.dev/skills/markdavidgan/apple-dev-skills/swift6-concurrency)<a href="https://agentmods.dev/skills/markdavidgan/apple-dev-skills/swift6-concurrency"><img src="https://agentmods.dev/badge/skills/markdavidgan/apple-dev-skills/swift6-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.
<a href="https://agentmods.dev/skills/markdavidgan/apple-dev-skills/swift6-concurrency"><img src="https://agentmods.dev/badge/skills/markdavidgan/apple-dev-skills/swift6-concurrency.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00074 | $0.05552 |
| Opus 5 | $0.00037 | $0.02776 |
| Sonnet 5 | $0.00015 | $0.01110 |
| Haiku 4.5 | $0.00007 | $0.00555 |
Grade A, and why
swift6-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 6d 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.
How it starts
The opening of the file, as written. The whole thing — 511 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Handle Swift 6 concurrency issues. Swift 6 enforces strict data isolation by default; most errors fall into a small number of patterns with known fixes.
Deep reference: For 8 comprehensive crash scenarios with WRONG/RIGHT pairs, load
ios26-api-reference/essentials/swift6.md. For expert-level patterns (actor isolation, migration strategies), loadios26-api-reference/guides/expert-swift6.md. For real-world community gotchas, loadios26-api-reference/intel/community-swift6.md. Live API verification (Optional): If Context7 MCP is installed, query it for the latest Swift concurrency documentation. Otherwise, use the static patterns in this skill and flag unfamiliar APIs as "unverified".
Core Philosophy
Start Single-Threaded, Profile Before Optimizing
Concurrency is a complexity tax. Apps should begin with all code on the main thread and only introduce concurrency when profiling data proves it's necessary.
- Use Instruments first. Run the Time Profiler to confirm that severe hangs are genuinely caused by main-thread blocking before converting code to run concurrently.
- Optimize without concurrency first. If code can be made faster algorithmically (better data structures, reduced work, caching), pursue that route before adding
async/awaitor background tasks. - Latency vs. throughput. Use
async/awaitto hide latency (network, disk). Useasync letorTaskGroupto exploit multiple CPU cores for parallel computation. Do not conflate the two.
When to Use Each Concurrency Tool
| Goal | Tool | Example |
|---|---|---|
| Hide I/O latency | async/await |
Network request, file read |
| Parallel CPU work | async let, TaskGroup |
Image processing, data parsing |
| Isolate shared mutable state | Custom actor |
Cache, network connection manager |
| Update UI safely | @MainActor |
ViewModel, ObservableObject |
Common Error Patterns
1. static property is not concurrency-safe
App Intent metadata and similar protocol requirements often use static var:
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.
- 6d ago First seen · 511 lines · 74 tokens per session scan A 22a282a7969b
swift6-concurrency is a skill published in the GitHub repository markdavidgan/apple-dev-skills (5 stars, last pushed 10d ago), licensed MIT. It adds 74 tokens to every session and 5,552 once invoked, about $0.0004 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 2026-09-03.
Other skills, from other repositories
asc-crash-triage
Triage TestFlight crashes, beta feedback, and performance diagnostics using asc. Use when the user asks about TF crashes, TestFlight crash reports, beta tester feedback, app hangs, disk writes, launch diagnostics, or wants a crash summary for a build or app.
swift-concurrency
Resolve Swift concurrency compiler errors, adopt approachable concurrency (SE-0466), and write data-race-safe async code. Use when fixing Sendable conformance errors, actor isolation warnings, or strict concurrency diagnostics; when adopting default MainActor isolation, @concurrent, nonisolated(nonsending), or…
swift-coding-guideline
Core Swift development workflows for Xcode and Swift tooling, including project setup, dependency management, concurrency guidance, language/runtime best practices, and troubleshooting build or package resolution issues. Use when working on Swift tasks across a codebase, especially package/tooling/runtime work and…
xcode-compilation-analyzer
Analyze Swift and mixed-language compile hotspots using build timing summaries and Swift frontend diagnostics, then produce a recommend-first source-level optimization plan. Use when a developer reports slow compilation, type-checking warnings, expensive clean-build compile phases, long CompileSwiftSources tasks…
spm-build-analysis
Analyze Swift Package Manager dependencies, package plugins, module variants, and CI-oriented build overhead that slow Xcode builds. Use when a developer suspects packages, plugins, or dependency graph shape are hurting clean or incremental build performance, mentions SPM slowness, package resolution time, build…
xcode-compilation-analyzer
Analyze Swift and mixed-language compile hotspots using build timing summaries and Swift frontend diagnostics, then produce a recommend-first source-level optimization plan. Use when a developer reports slow compilation, type-checking warnings, expensive clean-build compile phases, long CompileSwiftSources tasks…