Claude API Basics

Getting Started with the Claude API

Learn how to integrate Anthropic's Claude into your applications with the Messages API.

What is the Claude API?

The Claude API by Anthropic lets you integrate Claude's AI capabilities directly into your applications. Claude is a family of AI assistants known for:

Strong reasoning — Complex analysis and problem-solving
Long context — Process entire codebases or documents
Safety — Designed to be helpful, harmless, and honest
Tool use — Execute code, call functions, use external tools

Available Models

Model	Description	Best For
claude-opus-4	Most powerful	Complex analysis, research
claude-sonnet-4-5	Balanced	Most tasks
claude-haiku-3-5	Fastest/cheapest	Simple tasks, high volume

Getting an API Key

Sign up at console.anthropic.com
Navigate to API Keys
Create a new key
Store it securely (never in client-side code)

SDK Options

Anthropic provides official SDKs for:

Python: anthropic package
TypeScript/JavaScript: @anthropic-ai/sdk package

Example

typescript

// Install: npm install @anthropic-ai/sdk

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY, // from env
});

async function main() {
  const message = await client.messages.create({
    model: "claude-opus-4-5",
    max_tokens: 1024,
    messages: [
      {
        role: "user",
        content: "Explain the difference between REST and GraphQL in 3 sentences.",
      },
    ],
  });

  console.log(message.content[0].text);
}

main();

// Python equivalent:
// import anthropic
// client = anthropic.Anthropic()
// message = client.messages.create(
//   model="claude-opus-4-5",
//   max_tokens=1024,
//   messages=[{"role": "user", "content": "Hello, Claude!"}]
// )
// print(message.content[0].text)

Try it yourself — TYPESCRIPT