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 agentmods add skills/johnrogers/claude-swift-engineering/storekitnpx skills add johnrogers/claude-swift-engineering --skill storekitgit 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/storekit)<a href="https://agentmods.dev/skills/johnrogers/claude-swift-engineering/storekit"><img src="https://agentmods.dev/badge/skills/johnrogers/claude-swift-engineering/storekit.svg" alt="Measured on agentmods" 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 | $0.00046 | $0.00650 |
| Opus 5 | $0.00023 | $0.00325 |
| Sonnet 5 | $0.00009 | $0.00130 |
| Haiku 4.5 | $0.00005 | $0.00065 |
Grade A, and why
storekit 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 — 58 lines — stays where its author put it; the contents beside it link to each section on GitHub.
StoreKit
StoreKit 2 patterns for implementing in-app purchases with async/await APIs, automatic verification, and SwiftUI integration.
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 |
|---|---|
| Getting Started | Setting up .storekit configuration file, testing-first workflow |
| Products | Loading products, product types, purchasing with Product.purchase() |
| Subscriptions | Auto-renewable subscriptions, subscription groups, offers, renewal tracking |
| Transactions | Transaction listener, verification, finishing transactions, restore purchases |
| StoreKit Views | ProductView, SubscriptionStoreView, SubscriptionOfferView in SwiftUI |
Core Workflow
- Create
.storekitconfiguration file first (before any code) - Test purchases locally in Xcode simulator
- Implement centralized
StoreManagerwith@MainActor - Set up
Transaction.updateslistener at app launch - Display products with
ProductViewor custom UI - Always call
transaction.finish()after granting entitlements
Essential Architecture
@MainActor
final class StoreManager: ObservableObject {
@Published private(set) var products: [Product] = []
@Published private(set) var purchasedProductIDs: Set<String> = []
private var transactionListener: Task<Void, Never>?
init() {
transactionListener = listenForTransactions()
Task { await loadProducts() }
}
}
Common Mistakes
- Missing
.finish()calls on transactions — Forgetting to calltransaction.finish()after granting entitlements causes transactions to never complete. The user won't see their purchase reflected. Always callfinish().
What ships with it
5 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.
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 · 58 lines · 46 tokens per session scan A ece914648da1
storekit is a skill published in the GitHub repository johnrogers/claude-swift-engineering (228 stars, last pushed 7mo ago), licensed MIT. It adds 46 tokens to every session and 650 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.
Other skills, from other repositories
play-billing-library-version-upgrade
Use this skill when upgrading or migrating an Android project from any legacy Google Play Billing Library (PBL) version to the latest stable version of PBL.
asc-revenuecat-catalog-sync
Reconcile App Store Connect subscriptions and in-app purchases with RevenueCat products, entitlements, offerings, and packages using asc and RevenueCat MCP. Use when setting up or syncing subscription catalogs across ASC and RevenueCat.
google-play
Google Play Developer API (Android Publisher) integration with managed OAuth. Manage apps, subscriptions, in-app purchases, and reviews. Use this skill when users want to interact with Google Play Console programmatically. For other third party apps, use the api-gateway skill (https://clawhub.ai/byungkyu/api-gateway).
asc-iap-attach
Attach in-app purchases and subscriptions to an app version for App Store review. Use when the user has IAPs or subscriptions in "Ready to Submit" state that need to be included with a first-time version submission. Works for both first-time and subsequent submissions.
subscription-lifecycle
Generates StoreKit 2 subscription lifecycle management — grace periods, billing retry, offer codes, win-back offers, upgrade/downgrade paths, and subscription status monitoring. Use when user needs post-purchase subscription state handling beyond the initial paywall.
subscription-offers
Generates StoreKit 2 code for all subscription offer types — introductory, promotional, offer codes, and win-back. Includes eligibility checks, offer presentation, and the preferredSubscriptionOffer modifier. Use when adding subscription offers, free trials, or promotional pricing.