Whether you're using Claude on the web or via API, you'll likely encounter various error messages. This article systematically covers the most common Claude error codes and offers practical solutions to help you resume usage quickly.
Network Connection & Request Errors
Error message: "Connection error" or "Network anomaly".
Cause: Unstable local network, DNS resolution issues, or temporary Claude server fluctuation.
Solution: First check your network connection. Try switching Wi‑Fi or using mobile data. If the issue persists, clear your browser cache or switch browsers. API users should verify the request endpoint (e.g., https://api.anthropic.com) and confirm that port 443 is not blocked by a firewall.
Error code 400 Bad Request: Typically caused by malformed request parameters. Double‑check the JSON structure of your API call, ensure required fields (such as model and max_tokens) are correct, and that parameter values fall within allowed ranges.
Rate Limits & Token Exceeded
Error code 429 Too Many Requests: Indicates you've sent too many requests in a short period, triggering rate limiting.
Solution: Reduce your request frequency; add at least a 1‑second delay between API calls. Using Claude Pro or a team plan can provide higher request quotas. For web users, avoid rapid refreshing and wait a few minutes before continuing the conversation.
Error message: "Context length exceeded" or token limit reached.
Cause: The conversation history or input text is too long, exceeding the model's context window (e.g., Claude 3.5 Sonnet supports 200K tokens).
Solution: Shorten your input and remove unnecessary history. When calling the /messages endpoint, use the max_tokens parameter to control output length, or leverage Claude's "summarize history" feature to compress the context.
Account Verification & Permissions
Error code 403 Forbidden: Usually caused by an invalid, expired, or insufficiently permissioned API key. Go to the Anthropic Console to regenerate your API Key and ensure it's correctly added to the x-api-key header. If this error appears on the web, try logging out and back in.
Error message: "Your account has been locked" or "Verification required".
Cause: Too many incorrect password attempts in a short period, login from a new location, or triggered security policies.
Solution: Check your registered email for an unlock link and follow the instructions to reset your password. If you don't receive the email, contact Anthropic support. We recommend enabling two‑factor authentication (2FA) to improve account security.
Error code 500 Internal Server Error: This is a temporary server‑side issue that usually requires no action from you. Wait a few minutes and retry. If the error persists, check the Anthropic status page to confirm whether maintenance is ongoing.
