An API (Application Programming Interface) is a defined set of rules and protocols that allows one piece of software to request data or services from another. It is the standard way applications talk to each other over the internet.
When your weather app shows today's forecast, it is not generating that data itself. It sends a request to a weather API, which responds with the relevant data in a structured format (usually JSON). The app then displays that data to you. The API defines what you can ask for, how to ask for it, and what the response will look like.
Most web APIs follow the REST pattern, where you make HTTP requests (GET, POST, PUT, DELETE) to specific URLs called endpoints. Each endpoint returns a predictable response. For example, calling GET /api/btc-price on TerminalFeed returns the current Bitcoin price. Some APIs use GraphQL instead, letting clients specify exactly which fields they want.
APIs usually require authentication (via API keys, OAuth tokens, or JWTs) and enforce rate limits to prevent abuse. Good API documentation explains every endpoint, its parameters, expected responses, and error codes.
APIs are the backbone of modern software. Every dashboard, mobile app, and integration you use relies on APIs to fetch and send data. Understanding APIs is essential for developers building applications, and increasingly useful for non-developers who want to automate workflows or pull data into spreadsheets and tools.
TerminalFeed itself is powered by 20+ API endpoints. Every panel on the dashboard fetches data through our public API. You can explore all available endpoints at /api/. For a guide to free APIs you can use in your own projects, check out our article on 30+ Free APIs for 2026.