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 RevenueCat/play-billing-skills --skill understanding-billinggit clone --depth 1 https://github.com/RevenueCat/play-billing-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/revenuecat/play-billing-skills/understanding-billing)<a href="https://agentmods.dev/skills/revenuecat/play-billing-skills/understanding-billing"><img src="https://agentmods.dev/badge/skills/revenuecat/play-billing-skills/understanding-billing/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/revenuecat/play-billing-skills/understanding-billing"><img src="https://agentmods.dev/badge/skills/revenuecat/play-billing-skills/understanding-billing.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 | $0.00063 | $0.01511 |
| Opus 5 | $0.00032 | $0.00756 |
| Sonnet 5 | $0.00013 | $0.00302 |
| Haiku 4.5 | $0.00006 | $0.00151 |
Grade A, and why
understanding-billing 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 13d 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 — 121 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Phase 0: Intent
Tell the user: "I will orient you to Google Play Billing's three pillars, map your goal to the right pillar, and point you at the concrete skill to run next."
Phase 1: Discovery
Before touching code, confirm the developer understands the three pillars and the four actors. Each pillar owns a different slice of the system:
| Pillar | Surface | Role |
|---|---|---|
| Play Billing Library (PBL) | Android client, Gradle dep com.android.billingclient:billing-ktx |
Query products, launch purchase dialog, receive results on device |
| Google Play Developer API | Server REST API at androidpublisher.googleapis.com |
Verify purchases, manage subscriptions, manage catalog. Source of truth |
| Google Play Console | Web dashboard | Create products, set prices, configure RTDNs and API access |
A fourth piece, Cloud Pub/Sub, carries Real Time Developer Notifications (RTDNs) from Google to your backend when purchase or subscription state changes.
The four actors in every transaction:
| Actor | Responsibility |
|---|---|
| Your app | Query products, launch purchase flow, forward purchase tokens to backend |
| Google Play Services | System service that renders the purchase dialog and talks to Google's servers |
| Your backend | Verify tokens against the Developer API, store entitlements, process RTDNs |
| Google Play servers | Process payments, run renewals and payment recovery, emit RTDNs |
Ask the developer which of these surfaces they already have set up: Play Console account, service account credentials, Pub/Sub topic, backend, Android app.
Phase 2: Plan
Map the developer's goal to the pillar(s) they need, then to the next skill.
| Developer goal | Primary pillar | Next skill |
|---|---|---|
| First time onboarding, no account yet | Play Console | google-play/setup |
| Show prices and launch a purchase from the app | PBL | google-play/integrating-pbl |
| Verify a purchase token on the server | Developer API | google-play/server-verification |
| Receive renewal and cancellation events | RTDN plus Developer API | google-play/rtdn |
| Create or edit products, base plans, offers | Play Console or catalog API | google-play/catalog |
| Handle subscription lifecycle states | Developer API plus RTDN | google-play/subscription-lifecycle |
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.
- 13d ago First seen · 121 lines · 63 tokens per session scan A c651421e9d1a
understanding-billing is a skill published in the GitHub repository RevenueCat/play-billing-skills (53 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 63 tokens to every session and 1,511 once invoked, about $0.0003 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.
axiom-implement-iap
Use when the user wants to add in-app purchases, implement StoreKit 2, or set up subscriptions.
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).
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.