Show HN: A billing ledger on Postgres, tested with randomized invariants

Category: library

Tags: postgresql, billing, concurrency, webhooks, append-only-ledger, idempotency, testing

Score: 7.0/10 (Innovation: 6, Technical: 8, Documentation: 8, Utility: 6)

A framework-free TypeScript extraction of an EdTech platform's billing core, covering append-only lesson billing, hardened payment webhooks, and enumeration-safe login rate limiting on plain PostgreSQL. Its standout is rigorous concurrency work—deterministic lock tests, burst tests, randomized ledger invariants, and a mutation check that kills all 12 removed defences—plus a documented real bug the invariant test caught.

Target audience: Backend developers building payments/billing systems, especially those working with PostgreSQL and concurrency

Repository: https://github.com/alt-f6/edtech-billing-core · TypeScript · MIT · 1 stars

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