Status Codes

Every response opens with a three digit code, and the first digit tells you who to blame:

• 2xx worked. 200 OK, 201 Created.
• 3xx go somewhere else. 301 moved permanently, 302 found.
• 4xx the request was wrong. 404 not found, 401 unauthorized, 403 forbidden.
• 5xx the server broke. 500 internal error, 503 unavailable.

The 4xx and 5xx split is the useful one. 4xx is your fault, so fix the request: wrong path, missing token, bad data. 5xx is their fault, so retrying may help and changing your request will not.

Remember that a 404 is a perfectly successful request. The connection worked, the server understood, and its answer was "no such thing". curl exits 0.