APIs

An API lets a program request data from a service. The response can arrive successfully and still contain the wrong currency, a stale quote or an invalid price. This lesson decodes an offline JSON fixture and checks the fields needed by the calculation. It extends file parsing and exceptions to a service response; time-series checks address timestamps after parsing.

Learning objectives. By the end of this note you should be able to distinguish URL parameters from response data, interpret common status classes, decode JSON and validate required fields.