alpaca-broker-money-precision

Parse Alpaca's string-encoded money fields with decimal.Decimal, never float, and serialize back to strings when sending requests. Alpaca returns prices and amounts as JSON strings specifically to avoid binary float precision loss.

Alpaca accepts 2 decimal places for cash amounts and up to 9 decimal places for fractional share qty and notional values. Round or truncate to the target precision before the API call to avoid rejection or silent rounding.

Use either qty or notional, never both. Pass notional directly and let Alpaca compute the fill rather than reconstructing qty from notional divided by a fetched price, which introduces drift.

Rejections happen when amounts carry more decimal places than allowed or when binary floats introduce rounding artifacts. Explicitly truncate outgoing money to 2 decimal places with an intentional rounding mode before sending.

Store money as fixed-point decimal such as DECIMAL(20, 8), never float, and keep the raw values Alpaca sent verbatim alongside any converted values. Include an explicit currency column since some Alpaca rails are multi-currency.