Common Claude Error Codes and How to Fix Them

When using Claude, both the web version and the API can throw various errors that interrupt your work and hurt creative output. This article compiles the most common Claude error codes along with their solutions to help you resume use fast.

Auth Errors: 401/403

Receiving a 401 Unauthorized or 403 Forbidden usually means your API key is invalid or you lack sufficient permissions. On the web version, if you see "Session expired" directly, you'll need to log in again.

Fix: Check that your API key is copied completely and contains no extra spaces. For the web version, try clearing your browser cache or switching to a different network before logging in. Also confirm your account hasn't been temporarily suspended due to policy violations.

Rate Limits & Quota Exhaustion: 429 Too Many Requests

Making too many consecutive API calls or frequently refreshing the web page (especially for free-tier users) can trigger a 429 status code. The system will show "Too many requests" and pause service for a period.

Fix: Add delays between requests—keep it under 20 calls per minute. API users can upgrade to a paid plan for higher rate limits. If you're on the free web version, disable any auto-refresh scripts and wait 15–30 minutes to resume.

Server Internal Error: 500 Internal Server Error

Occasionally you'll run into a 500 error, usually caused by a temporary Claude server glitch. You may see "Something went wrong" or the chat interface may fail to load entirely.

Do not resubmit requests repeatedly; wait for official fixes. Check the Anthropic status page to confirm server health. Typically the issue resolves within 15 minutes. If it persists for over an hour, contact support.

Network & Timeout Errors: Timeout/Connection Failed

When loading conversation lists or sending messages, unstable networks may cause Claude to show "Connection timeout" or "Unable to connect to server." This isn't a Claude problem per se.

Check your local network—switch to a wired connection or mobile hotspot. Flush your DNS cache (Windows: run ipconfig /flushdns, Mac: run sudo dscacheutil -flushcache). If you're using a proxy, disable it or switch nodes before retrying.

Empty Response from API

Some API users report receiving null values from Claude models without a clear error code. This usually happens due to malformed request parameters or content blocked by safety policies.

Check that the messages structure in your request body follows the official format—ensure the role is either user or assistant. Also review your input for sensitive words and try simplifying the prompt before resending. If the issue persists, enable developer console logging to pinpoint the exact cause.