API
Also: AI API
A way for software to talk to other software — specifically, a set of rules for how your application can send requests to Claude and receive responses back. Instead of a human typing into Claude.ai, your code sends a message to Anthropic's API and gets Claude's response back as data it can use. APIs are how Claude gets embedded in other products: your company's app, a custom internal tool, or an automated workflow.
In practice
You want Claude inside your own product — not sending users to Claude.ai. The API lets you do that: your app sends a message to Anthropic's servers, Claude responds, and your app shows the response. Every time a user types into your custom Claude-powered tool, an API call happens in the background.
Related concepts
Where API shows up
4 articlesThe official quickstart gets you to 'Hello, world.' This gets you to understanding why Claude gave you a worse answer than the web app — and exactly how to fix it.
Environment variables, rate limits, error handling, costs, and the things that bite you on your first production deploy. A practical checklist.
When your app has more than one user, naive retry logic is not enough. Token budgeting, per-user quotas, request queuing, and graceful degradation — in code.
Protect your API routes, tie conversations to users, and track per-user costs. The full integration from NextAuth setup to authenticated Claude calls.