Billing Doctor

Billing Doctor

Billing Doctor reads what happened to a Google Play purchase and tells you where it broke. It runs on your machine, calls nothing, changes nothing at Google, and shows its evidence. Not affiliated with Google.

It is for developers who run their own Google Play Billing backend, in Node, Python, PHP, Go or Java, with Capacitor, Flutter, React Native or native Android in front, and did not choose a subscription platform. It is the tool you run at 11 pm when a subscription broke.

Twenty seconds

The fixture below ships in the repository, so start from a checkout:

git clone https://github.com/lazytitan30/billing-doctor && cd billing-doctornpx billing-doctor diagnose fixtures/rules/G2-void-then-active.json

(The same fixtures ship inside the npm package: after npm install -g billing-doctor they are under $(npm root -g)/billing-doctor/fixtures/.)

billing-doctor 0.1.1: fixtures/rules/G2-void-then-active.json, 11 events, 1 finding: 1 high
HIGH  G2  Voided purchase, then a fetch reading ACTIVE, and no revoke  [certain]      evidence  #8 rtdn voidedPurchase tok_a1 [m-2] answered 200 (2026-09-04T10:00:00Z)                #9 api subscriptionsv2.get tok_a1 → 200 SUBSCRIPTION_STATE_ACTIVE ack ACKNOWLEDGED (2026-09-04T10:00:01Z)      mechanism tok_a1 was voided at #8 (the money went back); the fetch at #9 still answered ACTIVE and the ledger never revoked, so the refunded user keeps the tier.      Google    "(1) REFUND_TYPE_FULL_REFUND - The purchase has been fully voided."                RTDN reference: VoidedPurchaseNotification, read 2026-09-09: https://developer.android.com/google/play/billing/rtdn-reference      observed  Seen in a live app, 2026-08: after the voided-purchase notification, purchases.subscriptionsv2.get still answered SUBSCRIPTION_STATE_ACTIVE ...      next      Revoke tok_a1 now. In the handler, act on voidedPurchaseNotification directly: mark refunded and revoke, regardless of what subscriptionsv2.get answers afterwards.      fix       runbook G2 (billing-doctor rule G2)
1 finding: 1 highexit 1: a high finding is present

Every finding carries the events it rests on, the mechanism, Google's rule quoted with a dated link, a confidence (certain, likely, possible) and the next thing to check. Exit code 1 means a high finding exists, so the command can gate CI.

What it does

You give it a timeline: one JSON file with what happened to one purchase, assembled from your logs, your database, the Cloud Console and the support ticket. The notifications Google sent, the API answers, what your backend wrote, what the user said. Tokens are pseudonyms; nothing real goes in the file.

It checks the timeline against 97 rules in eleven groups. Every one of them rests on a sentence from Google's own documentation, quoted verbatim with the URL and the date it was read:

billing-doctor rules lists them; billing-doctor rule B1 prints one in full.

Install

Node 20 or later.

npm install -g billing-doctor

Or run it without installing: npx billing-doctor <command>.

Commands

Exit codes: 0 nothing to report, 1 a high finding (or an input that could not be decoded), 2 a usage or file error.

The timeline

docs/timeline-format.md is the contract. Six event kinds: app (what the device reported), api (a call to the Play Developer API and its answer), ledger (what the backend wrote), rtdn (a notification as received), support (what the user said), console (releases and config changes). A policy block says what your backend is supposed to do, so a rule can tell your policy from a bug.

{  "schema": "billing-doctor-timeline/1",  "app": { "packageName": "com.example.app", "billingLibrary": "8.0.0", "backend": "node" },  "policy": { "grantOn": ["SUBSCRIPTION_STATE_ACTIVE", "SUBSCRIPTION_STATE_IN_GRACE_PERIOD", "SUBSCRIPTION_STATE_CANCELED"], "ackWithinHours": 72 },  "events": [    { "t": "2026-09-01T10:00:00Z", "kind": "app", "type": "purchase_result", "token": "tok_a1", "productId": "basic_monthly", "purchaseState": "PURCHASED" },    { "t": "2026-09-01T10:00:02Z", "kind": "api", "call": "subscriptionsv2.get", "token": "tok_a1", "status": 200, "subscriptionState": "SUBSCRIPTION_STATE_ACTIVE", "acknowledgementState": "ACKNOWLEDGEMENT_STATE_PENDING", "expiryTime": "2026-10-01T10:00:00Z" },    { "t": "2026-09-01T10:00:03Z", "kind": "ledger", "op": "grant", "token": "tok_a1", "userId": "u_1", "idempotencyKey": "tok_a1:grant" }  ]}

The fixtures/ folder holds one minimal timeline per rule, three realistic weeks, and five correct lifecycles that must produce nothing. They are the test suite and the best way to learn the format: fixtures/README.md.

With a coding agent

The same engine is an MCP server over stdio, so Claude Code, Codex, Gemini CLI or Cursor can call it while you fix the bug. Tools: diagnose_timeline, explain_subscription_state, decode_rtdn, redact_text, list_rules, get_rule.

Configure it as command npx, args ["-y", "billing-doctor", "mcp"]. For Claude Code, this repository is also a plugin (claude --plugin-dir . from a checkout, with the skill /billing-doctor:diagnose); for Gemini CLI, gemini extensions install https://github.com/lazytitan30/billing-doctor.

The Incident Kit

The free tool is complete on its own. The paid Incident Kit is a folder of files that makes the fix faster: a runbook entry per rule (the symptom as the user reports it, the mechanism, the fix, the regression test to add), a set of realistic incident timelines to replay against your own handler in CI, a TypeScript reference implementation of a verify endpoint, an RTDN handler and a reconciliation job, and checklists for the Play Console, Cloud setup, license testing and the Billing Library 8 and 9 migration. Drop the folder next to the tool as ./billing-doctor-kit (or set BILLING_DOCTOR_KIT) and billing-doctor rule G2 prints the runbook. There is no licence server and no phone-home; the kit is files.

billingdoctor.dev — one runbook page per rule, forty incident timelines, the reference backend, and the checklists.

What is in it, concretely:

Updates for twelve months, as a new download when Google's rules change or a rule is added.

The one optional network feature

diagnose --fetch reads purchases.subscriptionsv2.get for every token in a timeline with your own service-account key and appends Google's answers as api events, so a timeline built from logs gets Google's current view of each purchase. Off by default; nothing goes anywhere but Google.

billing-doctor diagnose timeline.json --fetch --service-account ./key.json --token-map ./tokens.json --out augmented.json

The timeline keeps its pseudonyms: tokens.json maps tok_a1 to the real purchase token and stays on your machine; the appended events carry the pseudonym and the written file never contains a real token. The key needs the "View financial data" permission in the Play Console. Subscriptions only; one-time products are not fetched.

Privacy

No network calls by default. No telemetry, ever. Your logs never leave your machine. The one optional network feature above uses your own key and talks only to Google.

What it is not

Not an SDK, not a hosted service, not a subscription platform, not a dashboard, not legal or financial advice. It never acknowledges, consumes, refunds, revokes, cancels or defers anything. It does not diagnose Apple.

Where this comes from

The rules are Google's own documentation, turned into checks a machine can run. Every one of the 97 quotes a sentence Google published, with the page, the section and the date it was read, and all 97 live in one file (src/google/docs.ts) so a documentation change is a one-file diff with failing tests beside it. The sources are the Android developer site, the Play Developer API reference, the Play Console help centre and the Pub/Sub documentation.

Eight rules also carry a field observation from a live app, dated and marked as an observation, always beside Google's sentence and never in place of it. Those exist because documentation says what should happen and a support inbox says what does: a wrapper that never surfaces the response code, a plugin that returns the base plan id as the product id, a web fallback that resolves with nothing and looks like a sale.

Every rule has a fixture that proves it fires, and five correct lifecycles that must produce no findings at all; a false positive is a release blocker. When a rule misses an incident of yours, open an issue with a redacted timeline (good first incident); that is how the catalogue grows.

Contributing

npm test builds and runs everything; the runner needs Node 20.9 or newer for --test-concurrency, while the tool itself runs on 20.0 (checked there). One file runs alone: node --test tests/rules-B.test.js. A new rule needs its file in src/engine/rules, its Google fact in src/google/docs.ts (the only file with a Google fact, each dated), its fixture with an expected.json, and one line in src/engine/catalogue.ts. The five clean fixtures must stay at zero findings; a false positive is a release blocker.

Licence and trademarks

MIT. Google Play is a trademark of Google LLC. Billing Doctor is an independent project and is not affiliated with, endorsed by, or sponsored by Google.