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 5.5 | $0.00030 | $0.02221 |
| Sonnet 5.5 | $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 1mo 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.
- 1mo 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 2mo ago), licensed MIT. It adds 74 tokens to every session and 5,552 once invoked, about $0.0003 per session on Opus 5.5. 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.
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