How to beginner · 3 min read

How to call Claude API from JavaScript

Q: How to call Claude API from JavaScript

Use the anthropic JavaScript SDK to call the Claude API by creating an Anthropic client with your API key, then invoke client.messages.create() with the model name (e.g., claude-3-5-sonnet-20241022) and your messages. This approach provides a simple, secure way to interact with Claude from JavaScript.

Quick answer

Use the anthropic JavaScript SDK to call the Claude API by creating an Anthropic client with your API key, then invoke client.messages.create() with the model name (e.g., claude-3-5-sonnet-20241022) and your messages. This approach provides a simple, secure way to interact with Claude from JavaScript.

PREREQUISITES

Node.js 18+
Anthropic API key
npm install anthropic

Setup

Install the official anthropic SDK for JavaScript and set your API key as an environment variable.

Run npm install anthropic to install the SDK.
Set your API key in your environment: export ANTHROPIC_API_KEY=your_api_key (Linux/macOS) or set ANTHROPIC_API_KEY=your_api_key (Windows).

bash

npm install anthropic

Step by step

Here is a complete JavaScript example using the Anthropic SDK to call Claude. It sends a simple prompt and prints the response.

javascript

import anthropic from "anthropic";
import dotenv from "dotenv";
dotenv.config();

async function callClaude() {
  const client = new anthropic.Anthropic({ apiKey: process.env.ANTHROPIC_API_KEY });

  const response = await client.messages.create({
    model: "claude-3-5-sonnet-20241022",
    max_tokens: 300,
    system: "You are a helpful assistant.",
    messages: [
      { role: "user", content: "Hello Claude, how do I call your API from JavaScript?" }
    ]
  });

  console.log("Claude response:", response.content);
}

callClaude().catch(console.error);

output

Claude response: To call the Claude API from JavaScript, use the official Anthropic SDK, create a client with your API key, and call client.messages.create() with your prompt and model name.

Common variations

Async/await: The example uses async/await for clarity.
Streaming: The Anthropic SDK supports streaming responses for real-time output.
Different models: Replace claude-3-5-sonnet-20241022 with other Claude models as needed.
Environment variables: Use dotenv or your platform's secret manager to securely manage API keys.

Troubleshooting

If you get 401 Unauthorized, verify your ANTHROPIC_API_KEY is set correctly.
If the response is empty or times out, check your network connection and model name spelling.
For rate limits, consider adding retry logic or upgrading your API plan.

✅

Key Takeaways

Use the official anthropic JavaScript SDK to call Claude API securely and easily.
Set your API key in environment variables and never hardcode it in your code.
The client.messages.create() method requires model, system, and messages parameters.
You can switch Claude models by changing the model parameter string.
Handle common errors like unauthorized access and rate limits by checking API keys and network.

Verified 2026-04 · claude-3-5-sonnet-20241022

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