Question 1

What do HTTP status codes mean, and what are the 5 classes?

Accepted Answer

HTTP status codes are three-digit responses the server sends to indicate the result of a request. The first digit defines the class: 1xx (100-199) are informational — the request was received and processing continues; 2xx (200-299) mean success; 3xx (300-399) are redirects — the client must take further action to complete the request; 4xx (400-499) are client errors — the request was malformed or unauthorized; 5xx (500-599) are server errors — the server failed to fulfill an otherwise valid request. Understanding the class tells you immediately who is at fault: 4xx means the client sent something wrong, 5xx means the server has a problem. This is the first diagnostic step for any API or web debugging session.

Question 2

What is the most common HTTP status code seen in production?

Accepted Answer

Across the web, 200 OK is the most frequent response, followed by 304 Not Modified (caching), 404 Not Found, 301 Moved Permanently, and 403 Forbidden. In API monitoring, the codes that indicate real problems are 429 Too Many Requests (rate limiting — often a configurable threshold your team set too low), 500 Internal Server Error (unhandled exception), 502 Bad Gateway (upstream failure, typically a proxy or load balancer problem), 503 Service Unavailable (server overloaded or in maintenance), and 504 Gateway Timeout (upstream took too long). A spike in 5xx codes is almost always an infrastructure event; a spike in 429s is almost always a configuration or client-behavior event.

Question 3

How do I fix a 404, 500, and 503 error on my website?

Accepted Answer

404 Not Found: the URL doesn't exist on the server. Check for typos, removed pages without redirects, or incorrect path casing (case matters on Linux servers). Fix with a 301 redirect for moved content and a custom 404 page for the rest. 500 Internal Server Error: an unhandled exception in your application. Check application logs first, then PHP/Node/Python error logs, then file permissions (a 500 after a deployment is usually a permission or missing-dependency issue). 503 Service Unavailable: the server is overloaded or down for maintenance. Check server load and memory, restart the application, and use a maintenance-mode page with a 503 and Retry-After header so search engines know it's temporary. The systematic order: check the response body, check application logs, check the web server logs, check infrastructure metrics.

Question 4

What is the difference between 301, 302, 303, 307, and 308 redirects?

Accepted Answer

301 Moved Permanently and 308 Permanent Redirect both mean the resource moved permanently, but 301 allows the browser to change the method (POST may become GET) while 308 preserves the method and body — use 308 for permanent API endpoint moves. 302 Found and 307 Temporary Redirect both mean the move is temporary, with the same method-handling difference: 302 may change the method, 307 preserves it. 303 See Other is the odd one: it explicitly redirects to a GET of a different resource, commonly used after a POST to send the user to a result page (the Post/Redirect/Get pattern). For SEO, use 301 for moved pages so link equity transfers; use 308 only when you need the method preserved, which search engines treat similarly to 301.

Question 5

Why am I getting 429 Too Many Requests and how do I fix rate limiting?

Accepted Answer

429 Too Many Requests means you exceeded the rate limit the server enforces for your client (IP, API key, or user). The response should include a Retry-After header telling you when to try again. Common causes: a retry loop without backoff, multiple clients sharing one API key, or a limit set too low for legitimate traffic. Fixes: implement exponential backoff with jitter on retries, cache API responses, distribute requests across multiple keys/IPs if allowed, and verify your app isn't polling in a tight loop. If you control the server, check that your rate limiter isn't counting health checks or redundant calls, and raise the limit for authenticated requests where appropriate.

HTTP Status Codes

The five classes, at a glance

How to use this reference when debugging

1xx	Informational — the request is being processed. You almost never see these as a user; they are protocol-level messages (100 Continue, 101 Switching Protocols).
2xx	Success — the request worked. 200 OK is the universal success; 201 Created for new resources; 204 No Content when the response intentionally has no body.
3xx	Redirects — the client must do something else. 301/308 permanent, 302/307 temporary, 304 Not Modified (the cache is still valid — this is a good thing, not an error).
4xx	Client errors — the request was wrong. 400 Bad Request, 401 Unauthorized (no credentials), 403 Forbidden (credentials but no permission), 404 Not Found, 429 Too Many Requests. You or your client caused these.
5xx	Server errors — the server failed. 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout. These are on you (the server operator).