The HTTP spec defines a long list of status codes, but most developers only ever need to reliably distinguish a much smaller working set — and mixing a few of them up (403 vs 401, 502 vs 503) is a common source of confusion when debugging API integrations.
401 means "who are you", 403 means "I know who you are, and no"
401 Unauthorized actually means unauthenticated — the request is missing valid credentials entirely. 403 Forbidden means the server understood who's asking and is deliberately refusing anyway, often because of permissions. Treating them as interchangeable during debugging sends you down the wrong path — one is a credentials problem, the other is a policy problem.
502 vs 503 point at different failures
502 Bad Gateway usually means a reverse proxy or load balancer got an invalid response from an upstream server — the upstream is reachable but broken. 503 Service Unavailable typically means the server is deliberately refusing to handle the request right now (overloaded, in maintenance). Knowing which one you're looking at narrows down where to look first.
TeckForge's HTTP Status Code Reference is a searchable list of the status codes that actually show up in day-to-day API and web debugging, grouped by category, so you don't have to keep a mental lookup table or leave your current tab to check.
