Why crypto payment systems should treat every amount string as hostile input

A developer with production experience building crypto payment systems since 2018 argues that most precision-related bugs stem from skipping representability checks and leaving rounding behavior implicit. The core problem is that when an amount string with too many decimal places enters a system, it is often silently truncated to fit a database column rather than flagged or explicitly rounded. This creates reconciliation drift that surfaces much later and cannot be easily attributed to a source. The author advocates declaring rounding policy explicitly at each call site before any computation occurs, rather than relying on whatever a database column or arithmetic operation happens to produce. To enforce this, they built a parsing library called cryptomoney that refuses float inputs, rejects amounts finer than the asset allows, and requires developers to explicitly name a rounding mode when precision loss is acceptable.