Handling API Errors and Rate Limits

When you build applications relying on external APIs, you must assume the API will eventually fail. The network will drop, the servers will be overloaded, or you will run out of credits.

If your Node.js app crashes entirely because Claude didn't respond to one request, that's bad engineering.

The Try/Catch Block

Always wrap your API calls in a try/catch block. This prevents your entire server from crashing if an error occurs.

async function getSummary() {
  try {
    const response = await anthropic.messages.create({ ... });
    return response.content[0].text;
  } catch (error) {
    console.error("Failed to generate summary:", error.message);
    // Return a fallback message so the UI doesn't break
    return "Summary currently unavailable. Please try again later.";
  }
}

Common Errors

1. 401 Unauthorized: Your API key is wrong, expired, or missing. Check your .env file.
2. 400 Bad Request: You formatted the JSON payload incorrectly (e.g., misspelled max_tokens or forgot the role in the messages array).
3. 529 Server Overloaded: Anthropic's servers are experiencing high traffic and cannot process your request right now.

Rate Limits (HTTP 429)

The most common error you will encounter as a developer is the 429 Too Many Requests error.

To prevent abuse and manage server load, Anthropic limits how many requests you can make per minute (RPM) and how many tokens you can process per minute (TPM).

If you write a loop that fires off 100 requests to Claude simultaneously, you will hit the rate limit instantly. Anthropic will reject the requests and throw a 429 error.

Implementing Exponential Backoff

If you get a 429 (Rate Limit) or 529 (Overloaded) error, you shouldn't just crash. You should wait a little bit and try again.

The industry standard approach is called Exponential Backoff. If a request fails, you wait 1 second and try again. If it fails again, you wait 2 seconds. Then 4 seconds. Then 8 seconds.

Many SDKs have basic retry logic built-in, but understanding the concept is crucial. When writing loops that process large amounts of data with Claude, you must intentionally slow your loop down (e.g., waiting 500ms between requests) to stay under the rate limit radar.