API
Also called application programming interface, REST API, or endpoint
A set of rules that lets one program ask another for data or actions, usually by sending a request to a URL and getting JSON back.
// Runs on the server, so the API key stays secret.
export async function getForecast(city: string) {
const response = await fetch(
`https://api.example.com/forecast?city=${encodeURIComponent(city)}`,
{ headers: { Authorization: `Bearer ${process.env.WEATHER_API_KEY}` } }
);
if (!response.ok) {
throw new Error(`Forecast request failed: ${response.status}`);
}
return (await response.json()) as { temp: number; sky: string };
}Show the current weather on the dashboard using a weather API. Call it from the server with the key in an environment variable, cache the result for 10 minutes, and show "Weather unavailable" if the request fails or takes longer than 5 seconds.
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API explained
API stands for application programming interface. On the web, an API is a set of URLs, called endpoints, that a program can call. Your app sends a request such as GET /forecast?city=Paris, and the service answers with a response, usually JSON, like { "temp": 18 }.
Apps use APIs for everything they do not build themselves: payments, maps, email, weather, and AI models. Your own backend also has an API that your frontend calls to load and save data.
Most APIs need a key to identify you. Keep it on the server, out of frontend code, and handle calls that fail, run slow, or hit a rate limit. Every response has a status code: 200 means it worked, 404 means not found, and 500 means the server failed.
Related terms
All termsFrontend and backend
The two halves of a web app: the frontend runs in the browser and draws what you see, and the backend runs on a server and handles data.
Database
An organized store for your app's data, such as users, posts, or orders, kept in tables so the app can save, find, and update it.
Tool call
A request from an AI model to run a named action, such as reading a file, searching, or running a command, whose result goes back to the model.
MCP
The Model Context Protocol: an open standard that connects AI apps to outside tools and data, such as files, databases, and design apps.
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