Open-Source CLI Tool Tests Payment Webhook Edge Cases Beyond HTTP 200 Status

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A developer tool called Invariant, published as an open-source npm package by Yavona Labs, aims to catch silent payment webhook bugs that standard monitoring tools like Datadog and Sentry miss. The CLI tests three common edge cases: duplicate event delivery causing double-credits, out-of-order webhook lifecycle events corrupting database state, and partial database mutations left behind after a server crash. These bugs can occur even when a webhook handler correctly returns HTTP 200, meaning no runtime exceptions are logged. Invariant works by injecting provider-accurate failure scenarios and verifying database post-conditions in under 10 seconds using a lightweight local probe route. The tool is available on GitHub and npm under @yavona/invariant, with an early access program currently open to developers.

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