What Are HTTP Status Codes? — Complete Guide

When you visit a website or request any resource from a web server, the server responds with a special code called an HTTP status code. This code indicates whether the request was successful, redirected, resulted in a client-side error, or faced a server-side error.

In simple terms — HTTP status codes tell you how things went behind the scenes when you loaded a page, fetched data, or submitted a form.

Why HTTP Status Codes Matter

They help browsers and clients know the result of a request
Useful for debugging and fixing website errors
Important for SEO and correct redirection behavior
Helps in building reliable web apps and APIs
Lets you understand when a page is missing, access denied, or server failed

Categories of HTTP Status Codes

HTTP status codes are grouped in five major categories, each starting with a number that indicates the type of response:

1xx – Informational

These codes are informational — they indicate that the request was received and processing is continuing.

Examples: 100 Continue, 101 Switching Protocols

2xx – Success

These codes show that the request was successful and the server responded correctly.

Common codes:

200 OK — The request was successful and the server returned the requested data.
201 Created — A new resource was created successfully.
204 No Content — The request succeeded but there is no content to send back.

3xx – Redirection

Indicates that further action is needed — typically redirecting to another URL.

Common codes:

301 Moved Permanently — The resource has permanently moved to a new URL.
302 Found / Temporary Redirect — The resource is temporarily at a different URL.
304 Not Modified — The resource has not changed since last request (used with caching).

4xx – Client Error

Means the request had a problem on client side — bad input, unauthorized access, or resource not found.

Common codes:

400 Bad Request — The server could not understand the request.
401 Unauthorized — Authentication is required / login needed.
403 Forbidden — Access is not allowed.
404 Not Found — The requested resource could not be found.
429 Too Many Requests — Client sent too many requests in short time.

5xx – Server Error

Indicates that server failed to process a valid request due to internal error.

Common codes:

500 Internal Server Error — General server error.
502 Bad Gateway — Server received an invalid response from upstream.
503 Service Unavailable — Server is busy or down for maintenance.
504 Gateway Timeout — Server took too long to respond.

Common HTTP Status Codes & Their Meaning

Code	Meaning	When You See It
200 OK	Success — everything worked	Page loaded, data fetched
301 Moved Permanently	Permanent redirect	Old URL changed to new one
302 Temporary Redirect	Temporary redirect	Short-term redirection
400 Bad Request	Client error	Invalid request/data
401 Unauthorized	Login required	Protected resource
403 Forbidden	Access denied	No permission
404 Not Found	Resource missing	Wrong URL or page removed
500 Internal Server Error	Server error	Server malfunction
503 Service Unavailable	Server busy/down	Site maintenance or overload

How to Use Status Codes in Web Development

Redirect old URLs to new ones using 301 to preserve SEO
Show friendly error pages for 404 or 500 errors
Use 401 / 403 to protect private content and ensure authorization
Use 204 when no content needs to be sent back (e.g. after form submission)
Use proper status codes in APIs for better client-server communication

FAQs — HTTP Status Codes

1. What does "200 OK" mean?

It means the request was successful and the server returned valid data.

2. Why do we get "404 Not Found"?

Because the URL requested does not exist or resource was deleted.

3. When should I use "301 Redirect"?

When a page or resource has permanently moved to a new URL.

4. What is difference between 500 and 503 errors?

500 is a general server error; 503 means server is currently unavailable (overloaded or down).

5. Are HTTP codes important for SEO?

Yes — search engines and browsers use them to index pages correctly and handle redirects or errors properly.

What Are — Programming Concepts Explained

Concepts & Explanations

What Are HTTP Status Codes? — Complete Guide