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 johnrogers/claude-swift-engineering --skill modern-swiftgit clone --depth 1 https://github.com/johnrogers/claude-swift-engineeringWrote 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/johnrogers/claude-swift-engineering/modern-swift)<a href="https://agentmods.dev/skills/johnrogers/claude-swift-engineering/modern-swift"><img src="https://agentmods.dev/badge/skills/johnrogers/claude-swift-engineering/modern-swift/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/johnrogers/claude-swift-engineering/modern-swift"><img src="https://agentmods.dev/badge/skills/johnrogers/claude-swift-engineering/modern-swift.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 | $0.00041 | $0.00894 |
| Opus 5 | $0.00020 | $0.00447 |
| Sonnet 5 | $0.00008 | $0.00179 |
| Haiku 4.5 | $0.00004 | $0.00089 |
Grade A, and why
modern-swift 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.
How it starts
The opening of the file, as written. The whole thing — 61 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Modern Swift (6.2+)
Swift 6.2 introduces strict compile-time concurrency checking with async/await, actors, and Sendable constraints that prevent data races at compile time instead of runtime. This is the foundation of safe concurrent Swift.
Overview
Modern Swift replaces older concurrency patterns (completion handlers, DispatchQueue, locks) with compiler-enforced safety. The core principle: if it compiles with strict concurrency enabled, it cannot have data races.
Quick Reference
| Need | Use | NOT |
|---|---|---|
| Async operation | async/await |
Completion handlers |
| Main thread work | @MainActor |
DispatchQueue.main |
| Shared mutable state | actor |
Locks, serial queues |
| Parallel tasks | TaskGroup |
DispatchGroup |
| Thread safety | Sendable |
@unchecked everywhere |
Core Workflow
When writing async Swift code:
- Mark async functions with
async, call withawait - Apply
@MainActorto view models and UI-updating code - Use
actorinstead of locks for shared mutable state - Check
Task.isCancelledor callTask.checkCancellation()in loops - Enable strict concurrency in Package.swift for compile-time safety
Reference Loading Guide
ALWAYS load reference files if there is even a small chance the content may be required. It's better to have the context than to miss a pattern or make a mistake.
| Reference | Load When |
|---|---|
| Concurrency Essentials | Writing async code, converting completion handlers, using await |
| Swift 6 Concurrency | Using @concurrent, nonisolated(unsafe), or actor patterns |
| Task Groups | Running multiple async operations in parallel |
| Task Cancellation | Implementing long-running or cancellable operations |
| Strict Concurrency | Enabling Swift 6 strict mode or fixing Sendable errors |
| Macros | Using or understanding Swift macros like @Observable |
| Modern Attributes | Migrating legacy code or using @preconcurrency, @backDeployed |
| Migration Patterns | Modernizing delegate patterns or UIKit views |
What ships with it
8 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.
- references/concurrency-essentials.md 3.4 KB
- references/macros.md 3.3 KB
- references/migration-patterns.md 3.7 KB
- references/modern-attributes.md 3.4 KB
- references/strict-concurrency.md 5.0 KB
- references/swift6-concurrency.md 5.2 KB
- references/task-cancellation.md 2.8 KB
- references/task-groups.md 2.7 KB
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 · 61 lines · 41 tokens per session scan A 2846d3fde397
modern-swift is a skill published in the GitHub repository johnrogers/claude-swift-engineering (228 stars, last pushed 7mo ago), licensed MIT. It adds 41 tokens to every session and 894 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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