Fintech Engineering Handbook collects money-system design patterns

Category: Engineering post
Status: discussion
Sources: handbook, discussion
Summary: Voytek Pitula published a free online Fintech Engineering Handbook, last modified 2026-06-27, as a living document on building money systems. It covers representing money (precision, rounding, currency, FX), recording transactions (double-entry bookkeeping, audit trails, event sourcing), executing money flows (invariants, reservations, idempotency, resumability), external integrations (APIs, webhooks, reconciliation), segregation-of-duties controls, testing strategies, and end-to-end examples such as a crypto withdrawal and a card deposit. It reached the HN front page with over 280 points.
Why it matters: It consolidates recurring correctness and consistency patterns for payment and ledger systems into one reference, useful for engineers building or auditing financial flows.