Question 1

What is the difference between a 401 Unauthorized and a 403 Forbidden?

Accepted Answer

A 401 Unauthorized status code indicates that the server does not know who the client is. The request lacks valid authentication credentials, such as a missing or expired JWT (JSON Web Token) or API key. The client should resolve this by logging in. A 403 Forbidden status code indicates that the server knows exactly who the client is, but the client does not have the proper authorization or administrative permissions to perform the requested action. Logging in again will not solve a 403; the user's account must be granted higher privileges by an administrator.

Question 2

Does a 301 Redirect pass SEO link equity to the new page?

Accepted Answer

Yes, a 301 Moved Permanently status code is the industry standard method for preserving SEO rankings when changing URLs. When a search engine crawler like Googlebot encounters a 301, it understands that the old URL is permanently defunct. It will remove the old URL from the search index and transfer approximately 90% to 100% of the historical ranking power (link equity) to the new destination URL. Using a 302 Found (temporary redirect) instead will cause the search engine to keep the old URL indexed, failing to pass the ranking power to the new page.

Question 3

Why am I seeing a 502 Bad Gateway error on my website?

Accepted Answer

A 502 Bad Gateway error occurs in environments where a proxy server (like Cloudflare, Nginx, or an AWS Application Load Balancer) sits in front of your actual backend application server (like a Node.js or Python process). The proxy server successfully received the client's request and forwarded it to your backend server. However, your backend server either crashed, was restarting, or returned a malformed response that the proxy could not understand. The proxy server therefore returns a 502 to the client. You must check the error logs of your backend application server to diagnose why it failed to respond properly to the proxy.

Question 4

Can I invent my own custom HTTP status codes?

Accepted Answer

Technically, yes, but it is highly discouraged. The HTTP specification dictates that if a client receives an unrecognized status code, it must treat it according to its class (the first digit). If you invent a custom code 499, a browser will simply treat it as a generic 400 Bad Request. However, inventing custom codes violates standard protocol and will confuse third-party developers, monitoring tools, and caching layers that expect standard IANA-registered codes. If you need to communicate highly specific business logic errors, you should return a standard 400 or 422 status code and include a detailed, custom error code inside the JSON response body.

Question 5

What is the difference between 503 Service Unavailable and 504 Gateway Timeout?

Accepted Answer

A 503 Service Unavailable means the server is actively rejecting requests. The server is alive and functioning enough to say, "I am too busy right now, or I am down for scheduled maintenance." It is an intentional, immediate rejection, often accompanied by a Retry-After header. A 504 Gateway Timeout, on the other hand, means a proxy server forwarded a request to a backend server, but the backend server took too long to respond. The proxy server waited for a predetermined amount of time (e.g., 30 seconds), gave up, and returned a 504 to the client. A 503 is an active refusal; a 504 is a failure due to latency.

Question 6

Is it acceptable to return a 200 OK for a failed request?

Accepted Answer

No, returning a 200 OK for a failed request is a severe anti-pattern in RESTful API design. HTTP status codes exist specifically to leverage the infrastructure of the internet. If you return a 200 OK for a database error and put the error message in the JSON body, your CDN might cache that error page, your load balancer will think the server is perfectly healthy, and your automated alerting tools will fail to notify you of the outage. You must always use a 4xx code for client errors and a 5xx code for server errors to ensure network infrastructure functions correctly.

HTTP Status Codes Reference

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