Claude Client

A production-ready TypeScript client for Anthropic Claude API with comprehensive features.

Features

• TypeScript client for Claude Sonnet 4 (claude-sonnet-4-20250514)
• Synchronous and asynchronous responses
• Streaming response capability
• Token usage control and context window monitoring
• API key-based authentication
• Automatic retries with exponential backoff and jitter
• Complete npm package structure
• Conversation history management
• Prompt template support
• Express and Fastify framework integrations
• Comprehensive error handling with retry logic
• Circuit breaker patterns for production use
• Extensive TypeScript types and interfaces
• Latest TypeScript 5.8.3 and Node.js 22.x support Native TypeScript support with Node.js experimental features Production-ready error handling and logging OpenAPI 3.0 specification

Basic usage

import { ClaudeClient } from "@your-org/claude-client";

const client = new ClaudeClient({
  apiKey: process.env.ANTHROPIC_API_KEY!,
  model: "claude-sonnet-4-20250514",
  maxTokens: 1024,
});

// Synchronous message
const response = await client.sendMessage([
  { role: "user", content: "Hello, Claude!" },
]);

console.log(response.content[0].text);

// Streaming message
for await (const chunk of client.streamMessage([
  { role: "user", content: "Tell me a story" },
])) {
  process.stdout.write(chunk);
}

// Token counting
const tokenCount = await client.countTokens({
  model: "claude-sonnet-4-20250514",
  messages: [{ role: "user", content: "Hello" }],
});
console.log(`Tokens: ${tokenCount.input_tokens}`);

Fastify integration

import Fastify from "fastify";
import claudePlugin from "@your-org/claude-client/fastify";
import { ClaudeClient } from "@your-org/claude-client";

const fastify = Fastify();
const client = new ClaudeClient({ apiKey: process.env.ANTHROPIC_API_KEY! });

await fastify.register(claudePlugin, {
  client,
  parseMessages: (request) => request.body.messages,
});

fastify.post("/chat", async (request, reply) => {
  const response = await fastify.claude.sendMessage(request.claudeMessages);
  return response;
});

Express integration

import { ClaudeClient } from "@magj/claude-client";

const client = new ClaudeClient({
  apiKey: process.env.ANTHROPIC_API_KEY!,
  model: "claude-sonnet-4-20250514",
  maxTokens: 1024,
});

// Synchronous message
const response = await client.sendMessage([
  { role: "user", content: "Hello, Claude!" },
]);

console.log(response.content[0].text);

// Streaming message
for await (const chunk of client.streamMessage([
  { role: "user", content: "Tell me a story" },
])) {
  process.stdout.write(chunk);
}

// Token counting
const tokenCount = await client.countTokens({
  model: "claude-sonnet-4-20250514",
  messages: [{ role: "user", content: "Hello" }],
});
console.log(`Tokens: ${tokenCountinput_tokens}`);

Local Development Setup

1. Install and Link Locally

# Clone and setup
git clone <your-repo>
cd claude-client
npm install

# Build the package
npm run build

# Link locally for development
npm link

# In your project
npm link @your-org/claude-client

2. Development Workflow

# Watch mode for development
npm run dev

# Type checking
npm run type-check

# Run tests
npm test

# Lint and format
npm run lint:fix
npm run format

# Generate documentation
npm run docs:api
npm run docs:openapi

3. Testing

# Run all tests
npm test

# Run with coverage
npm run test:ci

# Watch mode
npm test -- --watch

Production Deployment

1. Build and Publish

# Build production version
npm run build

# Validate OpenAPI spec
npm run validate

# Publish to npm
npm publish

2. Environment Variables

ANTHROPIC_API_KEY=your_api_key
ANTHROPIC_ORGANIZATION_ID=your_org_id  # Optional