Client error

401 401 Unauthorized

Authentication is required and either was not supplied or was not accepted. Despite the name it means unauthenticated, not forbidden.

Common causes

Missing or expired token, wrong API key, expired session.
A WWW-Authenticate challenge from HTTP basic auth — a staging site left protected is a classic.

How to fix it

Check that the credential is being sent and has not expired.
If a staging environment is behind basic auth, exclude your monitoring checks or they will alert forever.

See what a site actually returns

Run a live check and read the real status code, headers and timings.

Check a website

Other status codes

200 OK 201 Created 204 No Content 206 Partial Content 301 Moved Permanently 302 Found 303 See Other 304 Not Modified 307 Temporary Redirect 308 Permanent Redirect 400 Bad Request 403 Forbidden 404 Not Found 405 Method Not Allowed 408 Request Timeout 410 Gone 413 Payload Too Large 418 I'm a Teapot 429 Too Many Requests 451 Unavailable For Legal Reasons 500 Internal Server Error 501 Not Implemented 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout 507 Insufficient Storage 508 Loop Detected 521 Web Server Is Down 522 Connection Timed Out 523 Origin Is Unreachable 525 SSL Handshake Failed