API Reference

Complete reference for the Claude API.

Overview

The Claude API allows you to integrate Claude’s capabilities into your applications. This guide covers authentication, making requests, and handling responses.

Authentication

All API requests require an API key. Get your API key from the Anthropic Console.

export ANTHROPIC_API_KEY='your-api-key-here'

Quick Start

Python

import anthropic
 
client = anthropic.Anthropic(
    api_key="your-api-key-here",
)
 
message = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude!"}
    ]
)
 
print(message.content)

JavaScript

import Anthropic from "@anthropic-ai/sdk";
 
const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});
 
const message = await client.messages.create({
  model: "claude-3-5-sonnet-20241022",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "Hello, Claude!" }
  ]
});
 
console.log(message.content);

Available Models

Model	Description	Context Window
claude-3-5-sonnet-20241022	Latest and most capable model	200K tokens
claude-3-opus-20240229	High intelligence for complex tasks	200K tokens
claude-3-haiku-20240307	Fast and cost-effective	200K tokens

Key Concepts

Messages API

The Messages API is the primary way to interact with Claude.

Request Parameters

model (string, required): The model to use
messages (array, required): Array of message objects
max_tokens (integer, required): Maximum tokens to generate
temperature (float, optional): Randomness in responses (0-1)
system (string, optional): System prompt to guide behavior

Response Format

{
  "id": "msg_01XFDUDYJgAACzvnptvVoYEL",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hello! How can I help you today?"
    }
  ],
  "model": "claude-3-5-sonnet-20241022",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 12,
    "output_tokens": 25
  }
}

Advanced Features

Streaming

Enable streaming for real-time responses:

with client.messages.stream(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello!"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

Vision

Claude can analyze images:

message = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "image",
                    "source": {
                        "type": "base64",
                        "media_type": "image/jpeg",
                        "data": "/9j/4AAQSkZJRg...",
                    },
                },
                {
                    "type": "text",
                    "text": "What's in this image?"
                }
            ],
        }
    ],
)

Tool Use

Enable Claude to use tools and functions:

tools = [
    {
        "name": "get_weather",
        "description": "Get weather information for a location",
        "input_schema": {
            "type": "object",
            "properties": {
                "location": {
                    "type": "string",
                    "description": "City name"
                }
            },
            "required": ["location"]
        }
    }
]
 
message = client.messages.create(
    model="claude-3-5-sonnet-20241022",
    max_tokens=1024,
    tools=tools,
    messages=[{"role": "user", "content": "What's the weather in Tokyo?"}]
)

Best Practices

Rate Limiting: Implement proper rate limiting and retry logic
Error Handling: Handle API errors gracefully
Token Management: Monitor token usage to optimize costs
Caching: Cache responses when appropriate
Security: Never expose API keys in client-side code

Rate Limits

Tier	Requests per minute	Tokens per minute
Free	50	40,000
Pro	1,000	400,000
Enterprise	Custom	Custom

Error Handling

Common error codes:

400: Invalid request
401: Authentication error
403: Permission denied
429: Rate limit exceeded
500: Server error

try:
    message = client.messages.create(...)
except anthropic.APIError as e:
    print(f"API error: {e}")
except anthropic.RateLimitError as e:
    print(f"Rate limit exceeded: {e}")

Resources

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