API

An API, or application programming interface, lets one piece of software talk to another, for example your app sending text to an AI model and getting a reply.

In practice: Instead of using a tool through its website, developers call its API from their own code or from automation tools. AI companies sell model access through APIs, usually priced per token, image or second of audio.

Why it matters when picking a tool

An API matters if you want to connect a tool to your own systems or automate it. Check whether it is included in your plan or billed separately, the rate limits, and the quality of the documentation.