An API is a structured way for one piece of software to talk to another by sending requests and receiving responses over a defined set of rules. In web development, an API often means an HTTP interface where a client sends a request to a server and gets back JSON or another machine readable format. Each API exposes operations as endpoints that describe what you can ask for or change. APIs hide internal implementation details so callers only need to know the contract, not the underlying code or database. Good APIs are consistent, predictable, and well documented so both humans and machines can use them safely. Many modern systems are built as collections of services that communicate almost entirely through APIs. When you use a mobile app, it is usually calling a backend web application API behind the scenes. APIs can be public, partner only, or private to a single organization. They are a key building block whenever you integrate third party services such as payments, email, or analytics.
how it works
An API request usually travels over a network protocol such as HTTP or HTTPS. The client sends a request to an API endpoint URL with a method, headers, and sometimes a body, and then the server returns a response with a status code and data. Many APIs exchange data using JSON, which makes it easy to read and parse. Authentication is often handled with tokens, JWTs, or API keys to control who can call which operations. Inside the service, API handlers will usually talk to a database, cache, or other internal services before building the final response. Designing stable APIs requires attention to versioning and backward compatibility so existing clients continue to work as the system evolves.