diegosouzapw Anthropic Claude API
Official TypeScript SDK for Anthropic's Claude AI. Access Claude models for chat, tool use, vision, and extended thinking.
Quick Start
npm install @anthropic-ai/sdk
Setup
import Anthropic from '@anthropic-ai/sdk';
const anthropic = new Anthropic({
apiKey: process.env.ANTHROPIC_API_KEY,
});
Messages API
Basic Message
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [
{ role: 'user', content: 'Hello, Claude!' },
],
});
console.log(message.content[0].text);
System Prompt
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
system: 'You are a helpful coding assistant.',
messages: [
{ role: 'user', content: 'Explain async/await in JavaScript' },
],
});
Multi-turn Conversation
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [
{ role: 'user', content: 'What is TypeScript?' },
{ role: 'assistant', content: 'TypeScript is a typed superset of JavaScript...' },
{ role: 'user', content: 'How do I define an interface?' },
],
});
Streaming
Basic Streaming
const stream = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [{ role: 'user', content: 'Tell me a story' }],
stream: true,
});
for await (const event of stream) {
if (event.type === 'content_block_delta' && event.delta.type === 'text_delta') {
process.stdout.write(event.delta.text);
}
}
Using .stream() Helper
const stream = anthropic.messages.stream({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [{ role: 'user', content: 'Hello' }],
});
stream.on('text', (text) => {
process.stdout.write(text);
});
const finalMessage = await stream.finalMessage();
Stream Events
const stream = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [{ role: 'user', content: 'Hello' }],
stream: true,
});
for await (const event of stream) {
switch (event.type) {
case 'message_start':
console.log('Started:', event.message.id);
break;
case 'content_block_start':
console.log('Block started:', event.content_block.type);
break;
case 'content_block_delta':
if (event.delta.type === 'text_delta') {
process.stdout.write(event.delta.text);
}
break;
case 'content_block_stop':
console.log('Block stopped');
break;
case 'message_stop':
console.log('Message complete');
break;
}
}
Tool Use (Function Calling)
const tools = [
{
name: 'get_weather',
description: 'Get the current weather for a location',
input_schema: {
type: 'object',
properties: {
location: {
type: 'string',
description: 'City name, e.g., San Francisco',
},
unit: {
type: 'string',
enum: ['celsius', 'fahrenheit'],
},
},
required: ['location'],
},
},
];
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
tools,
messages: [
{ role: 'user', content: 'What is the weather in Tokyo?' },
],
});
// Check for tool use
const toolUse = message.content.find((block) => block.type === 'tool_use');
if (toolUse) {
// Execute the tool
const weatherData = await getWeather(toolUse.input.location);
// Send result back
const finalMessage = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
tools,
messages: [
{ role: 'user', content: 'What is the weather in Tokyo?' },
{ role: 'assistant', content: message.content },
{
role: 'user',
content: [
{
type: 'tool_result',
tool_use_id: toolUse.id,
content: JSON.stringify(weatherData),
},
],
},
],
});
}
Vision (Image Analysis)
URL Image
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [
{
role: 'user',
content: [
{
type: 'image',
source: {
type: 'url',
url: 'https://example.com/image.jpg',
},
},
{
type: 'text',
text: 'What is in this image?',
},
],
},
],
});
Base64 Image
import fs from 'fs';
const imageData = fs.readFileSync('image.jpg').toString('base64');
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [
{
role: 'user',
content: [
{
type: 'image',
source: {
type: 'base64',
media_type: 'image/jpeg',
data: imageData,
},
},
{
type: 'text',
text: 'Describe this image in detail',
},
],
},
],
});
Extended Thinking
For complex reasoning tasks, enable extended thinking.
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 16000,
thinking: {
type: 'enabled',
budget_tokens: 10000,
},
messages: [
{ role: 'user', content: 'Solve this complex math problem...' },
],
});
// Access thinking blocks
for (const block of message.content) {
if (block.type === 'thinking') {
console.log('Thinking:', block.thinking);
} else if (block.type === 'text') {
console.log('Response:', block.text);
}
}
PDF Support
import fs from 'fs';
const pdfData = fs.readFileSync('document.pdf').toString('base64');
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [
{
role: 'user',
content: [
{
type: 'document',
source: {
type: 'base64',
media_type: 'application/pdf',
data: pdfData,
},
},
{
type: 'text',
text: 'Summarize this document',
},
],
},
],
});
Next.js API Route
// app/api/chat/route.ts
import Anthropic from '@anthropic-ai/sdk';
import { AnthropicStream, StreamingTextResponse } from 'ai';
const anthropic = new Anthropic();
export async function POST(request: Request) {
const { messages } = await request.json();
const response = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages,
stream: true,
});
const stream = AnthropicStream(response);
return new StreamingTextResponse(stream);
}
Manual Streaming
// app/api/chat/route.ts
import Anthropic from '@anthropic-ai/sdk';
const anthropic = new Anthropic();
export async function POST(request: Request) {
const { prompt } = await request.json();
const stream = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [{ role: 'user', content: prompt }],
stream: true,
});
const encoder = new TextEncoder();
const readable = new ReadableStream({
async start(controller) {
for await (const event of stream) {
if (event.type === 'content_block_delta' && event.delta.type === 'text_delta') {
controller.enqueue(encoder.encode(event.delta.text));
}
}
controller.close();
},
});
return new Response(readable, {
headers: { 'Content-Type': 'text/plain; charset=utf-8' },
});
}
Error Handling
import Anthropic from '@anthropic-ai/sdk';
try {
const message = await anthropic.messages.create({
model: 'claude-sonnet-4-20250514',
max_tokens: 1024,
messages: [{ role: 'user', content: 'Hello' }],
});
} catch (error) {
if (error instanceof Anthropic.APIError) {
console.error('Status:', error.status);
console.error('Message:', error.message);
if (error.status === 429) {
// Rate limited
} else if (error.status === 401) {
// Invalid API key
} else if (error.status === 400) {
// Bad request
}
}
}
Counting Tokens
const tokenCount = await anthropic.messages.countTokens({
model: 'claude-sonnet-4-20250514',
messages: [
{ role: 'user', content: 'Hello, how are you?' },
],
});
console.log('Input tokens:', tokenCount.input_tokens);
Models
| Model | ID | Best For |
|---|---|---|
| Claude Opus 4 | claude-opus-4-20250514 | Complex tasks, research |
| Claude Sonnet 4 | claude-sonnet-4-20250514 | Balanced performance |
| Claude Haiku 4 | claude-haiku-4-20250514 | Fast, simple tasks |
Environment Variables
ANTHROPIC_API_KEY=sk-ant-xxxxxxxx
Best Practices
- Stream for long responses - Better UX and partial recovery
- Use system prompts - Set behavior and context
- Handle tool use loops - Multiple back-and-forth may be needed
- Enable extended thinking - For complex reasoning tasks
- Set appropriate max_tokens - Control response length
- Implement retries - Handle rate limits gracefully
- Use message batching - For batch processing workloads