Track 4 · API & Agents

Build Your First Claude API App in 5 Steps

Your first project. 20 minutes.

The Anthropic API gives you direct access to Claude models. This guide walks you through authentication, your first message, streaming, tool use, and the patterns you need to build reliable production systems.

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The Claude API (Anthropic Messages API) lets you build applications that use Claude programmatically. Install the SDK with pip install anthropic or npm install @anthropic-ai/sdk, set your API key, and call client.messages.create() with a model, system prompt, and messages array. Claude supports streaming, tool use, vision, and extended thinking.

Core Concepts

How the Claude API works

Messages API

Stateless request/response. You send the full conversation history each time. Claude returns a message object with usage statistics.

Streaming

Server-sent events deliver tokens as they are generated. Critical for chat interfaces and long-running responses.

Tool use

Define tools with JSON Schema. Claude calls them intelligently, you execute them, and the results feed back into the conversation.

System prompts

Set Claude's persona, constraints, and context via the system parameter. Cached system prompts reduce latency and cost.

Tutorial

Getting started step by step

01
Get your API key

Sign up at console.anthropic.com. Free tier includes enough credits to experiment. Production usage is pay-per-token.

02
Install the SDK

The Anthropic SDK is available for Python and TypeScript/JavaScript. Both are officially maintained.

JavaScript / TypeScript
npm install @anthropic-ai/sdk
# or
pip install anthropic
03
Your first request

Send a message to Claude claude-sonnet-4-5 and get a response. The API is stateless — you manage conversation history.

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

const client = new Anthropic();
const msg = await client.messages.create({
  model: "claude-sonnet-4-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Hello, Claude" }],
});
console.log(msg.content);
04
Add streaming

For real-time UI responses, use the streaming API. Tokens arrive as they are generated — no waiting for the full response.

JavaScript / TypeScript
const stream = await client.messages.stream({
  model: "claude-sonnet-4-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Tell me a story" }],
});

for await (const chunk of stream) {
  process.stdout.write(chunk.delta?.text ?? "");
}
05
Use tool use

Give Claude tools like web search, database access, or custom functions. Claude decides when to call them and parses the results.

JavaScript / TypeScript
const response = await client.messages.create({
  model: "claude-sonnet-4-5",
  tools: [{
    name: "get_weather",
    description: "Get current weather",
    input_schema: {
      type: "object",
      properties: { location: { type: "string" } },
      required: ["location"],
    },
  }],
  messages: [{ role: "user", content: "Weather in San Diego?" }],
});

Go deeper in the API & Agents track

Track 4 covers the full production surface: error handling, retry logic, rate limiting, prompt caching, multi-agent orchestration, and evaluation. Interactive exercises with a live Claude sandbox so you practice every pattern hands-on.

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Frequently Asked Questions

What is the best way to learn the Claude API?

The best way to learn the Claude API is through hands-on tutorials that progress from basic message creation to advanced features like tool use and streaming. Claude Academy covers API development in Track 4.

Is the Claude API free?

The Claude API uses usage-based pricing. There is no free tier for the API itself, but costs are low for experimentation. Claude Academy courses that teach the API are free.

What programming languages does the Claude API support?

Anthropic provides official SDKs for Python and TypeScript/JavaScript. The REST API works with any language that can make HTTP requests.

What is the difference between the Claude API and Claude.ai?

Claude.ai is a web interface for chatting with Claude directly. The Claude API is a programmatic interface for building applications that use Claude as a backend. The API supports tool use, streaming, batch processing, and custom system prompts that the web interface does not expose.

How do I handle rate limits with the Claude API?

Implement exponential backoff with jitter on 429 responses. The Anthropic SDK handles retries automatically. For high-throughput workloads, use the Batch API for 50% cost savings and no rate limit concerns. Monitor your usage tier and request limit increases through the Anthropic console.

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