FREE TOOL · BREAK MY CHECKOUT

One payment.
Five deliveries.

How many times does your app grant access? Replay a sample webhook and watch three handlers react.

Browser-only simulation. No Stripe keys, live payment requests or real payments.

SAMPLE PURCHASE · cs_demo_1

Try to grant access twice.

0 deliveries

No duplicate guard

0simulated access grants

Every successful delivery grants access again.

Event ID in memory

0simulated access grants

Forgets after restart. A claim before a crash can lose work.

Unique purchase + transaction

0simulated access grants

Models one DB commit: purchase key and access grant together.

Try this: reset → enable crash → deliver → deliver again. The memory guard skips unfinished work; the simulated transaction rolls back and can retry.

Delivery trace · last 6 actions
  1. No sample event delivered yet.
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NOW LOOK AT YOUR OWN CODE

What does your webhook actually do?

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What this teaches. What still needs testing.

Stripe can deliver an event more than once. A process-local event-ID guard can forget after a restart, or claim an event and crash before doing the work. Two distinct event IDs can also refer to the same purchase.

The third handler models a database transaction that commits a unique purchase key and a database access grant together. Here, the key represents a Checkout Session ID for one access grant. Pick a business key that fits your fulfillment operation. All three examples are simulated in browser memory; restarting the worker only clears the middle example.

A real integration still needs signature verification using the raw body, paid-status checks, concurrency and failure tests, and durable recovery. A database transaction cannot undo an external email or shipment: use an appropriate outbox and idempotent worker. This demo does not test your application, event ordering or delayed payment methods.

Read the primary sources: Stripe on duplicate events · Recovery and retries · DeployDoctor launch checks.