What is an API?
An API is a set of rules that lets one program ask another program for data or actions without knowing how it works inside.
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An API (application programming interface) is a menu of things a program lets other programs do. A restaurant menu is a good picture: you do not walk into the kitchen, you order from a fixed list and the kitchen handles the details. In the same way, an API lists the requests it accepts and the answers it gives back, and it hides everything else.
Libraries have APIs (the functions you can call), operating systems have APIs (how a program opens a file), and web services have APIs reached over HTTP. When a weather app shows today’s forecast, it called a weather API. When you log in with Google on another site, two APIs talked to each other. Reading the API documentation is the first step before using any service from code.
curl https://api.github.com/repos/python/cpythonSee also: What is a REST API? and What is HTTP?
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See also
- 0019 fetch with timeout, retries and proper error handling A reusable fetchJson helper for Node 20+ and browsers that adds a timeout, retries with backoff for temporary failures, and clear errors… Intermediate · Step by step · Any system Script Async code · Making requests 15 Oct 2026
- 0081 How an HTTP request works: methods, headers, and body An HTTP request is a short text message a client sends to a server: a method and path, some headers, and sometimes… Beginner · Explains an idea · Any system Article Making requests 15 Oct 2026
- 0083 Test a JSON API with curl A runnable bash script showing the curl commands you need most when testing an API: GET, POST JSON, custom headers, Bearer tokens,… Beginner · Step by step · Linux, macOS, Windows Script Authentication · Making requests 15 Oct 2026
- 0084 Tiny JSON echo server for testing HTTP clients A standard-library Python server that echoes back the method, path, query, headers, and body of every request, and can return any status… Intermediate · Step by step · Any system Script Files & automation · Making requests 15 Oct 2026
- 0085 fetch with timeout, retries, and exponential backoff A drop-in fetch wrapper that times out slow requests, retries network errors and 429/5xx responses with jittered exponential backoff, and honors Retry-After. Advanced · Step by step · Any system, Browser Script Async code · Making requests 15 Oct 2026
- 0087 CORS explained: why the browser blocks your request CORS is the browser rule that decides whether JavaScript on one origin may read a response from another. The server opts in… Intermediate · Explains an idea · Browser Article Async code · Making requests 15 Oct 2026
Repos in the wild
- Requests: HTTP for humans psf/requests Requests is the classic Python library for calling web APIs and downloading pages, with a simple API for GET and POST requests, headers, JSON and sessions. GitHub
- Axios axios/axios A promise-based HTTP client for browsers and Node.js with interceptors, automatic JSON handling, request cancellation and a consistent API in both environments. GitHub
- curl and libcurl (curl/curl) curl/curl The source of curl, the command-line tool for transferring data with URLs, and libcurl, the C library behind it that many other programs use for HTTP. GitHub
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- Dominik +835 chars