What Is an API? (Explained Without Jargon)

An API is a menu for programs: you order something specific and get back a defined response.

The restaurant menu analogy

Imagine a restaurant. You don't walk into the kitchen and cook yourself. You order from the menu, and the kitchen delivers exactly that. An API (Application Programming Interface) is that menu for software: one program asks another program for something specific and gets a defined response back.

A concrete example

A weather API receives a request like "weather for Berlin" and sends back structured data, say temperature and chance of rain. The app doesn't need to know how the weather is calculated — it just asks the API.

Why it matters for AI development

When you work with AI models, you're usually using an API: you send a prompt to a provider's API (e.g. Anthropic) and get the model's response back. AI agents also use APIs to talk to tools — a weather API, a database API, a search API.

In short

An API is a fixed, documented way for two programs to talk to each other, without either needing to know how the other works internally.