Application Programming Interface (API)

An Application Programming Interface (API) is a set of addresses one program calls to send another program a request and get structured data back, following rules the second program publishes for what it accepts and returns. The first program does not see how the second one works inside; it only sends a request shaped the way the rules describe and reads the reply. Picture a weather service: your to-do app calls the service's forecast address, passes a city and a date, and gets back a small block of labeled data saying the high is 72 and rain is likely. Your app never runs the forecast itself; it asks across a published boundary and trusts the answer.

Builder example

When you tell an AI assistant to pull live data into your app, such as the latest exchange rate or a customer's order status, it reaches that data through an API the other service exposes. The boundary is where things break: a renamed field, a slow response, or a returned error all surface here, so an assistant that pastes results in blindly will pass bad data downstream. Ask it to read the service's published rules first and handle the error reply, not only the success case.

Common confusion: An API is the published set of rules and addresses for talking to a service. One endpoint is a single address within that interface that handles one kind of request, so an API usually bundles many endpoints together.