Fintech Engineering Handbook: Money Handling Patterns
Original: Fintech Engineering Handbook
Why This Matters
Establishes standardized patterns for financial software development, addressing critical precision, data integrity, and compliance requirements.
Voytek Pitula published the Fintech Engineering Handbook, a comprehensive guide covering software engineering patterns for financial systems. The handbook addresses representing money, ledger management, fund flows, and compliance, targeting engineers joining fintech, existing fintech professionals, and those outside the sector learning financial system architecture.
The Fintech Engineering Handbook is a living document authored by Voytek Pitula that outlines essential patterns for building reliable money-handling software systems. The resource is organized around three core principles: No Invented Data (preventing duplicates and arbitrary balance updates through idempotency and reconciliation), No Lost Data (tracking all transactions via event sourcing, audit trails, and immutability), and No Trust (verifying external providers and cross-checking data sources). The handbook covers money representation methods including floating-point, arbitrary precision, minor-units precision, and crypto-specific approaches using integer-smallest-unit models. Key topics include double-entry bookkeeping, value time versus booking time versus settlement time, fund reservation, overdraft handling, idempotency, full resumability, webhook consumption, reliable notifications via outbox and change data capture patterns, and reconciliation. Additional sections address controls, segregation of duties, four-eyes principles, access control, and change trail management. The appendices provide domain knowledge on accounting, ledgers, money and foreign exchange, transactions and settlement timing, payments and card rails, trading and markets, custody and crypto, and compliance and regulation. End-to-end examples demonstrate workflows including crypto withdrawal, card deposits, and in-app conversions with cashback. The handbook was last modified June 27, 2026, and welcomes community contributions.