When you use the internet, you’re actually talking to websites without realizing it. This talk happens through a special set of rules called HTTP, which stands for Hypertext Transfer Protocol. Imagine it like a secret code that helps your computer and websites understand each other.
So, when you ask for a web page (like clicking on a link or typing in a web address), your computer sends a message in this secret code to the computer that has the webpage you want. We call this computer the “server.” The server gets your message and then sends a reply, also in the same secret code. This reply has a special three-digit number that tells your computer what happened with your request. These numbers are known as “HTTP response status codes.”
These response codes are like a quick message from the server to your computer. They’re super important because they tell your computer if everything went well or if there was a problem. These codes help people who build websites, fix issues, and make sure you have a good experience online.
In this article, we’ll give you a big list of these response codes, explain what they mean, and talk about when and why they show up.
Understanding HTTP Response Status Codes
HTTP response status codes are three-digit numerical codes that inform the client (usually your web browser) about the outcome of a requested resource or operation. They are grouped into five classes, each with its own significance:
Informational Responses (1xx): These codes indicate that the request has been received and is being processed. They are not frequently encountered in web development, but they provide information about the status of the request. For instance, the code 100 (Continue) means that the server has received the initial part of the request and is waiting for the client to continue.
Successful Responses (2xx): These codes signify that the request was successfully received, understood, and accepted. In other words, everything went well. The most commonly encountered status code in this category is 200 (OK), which means the request was successful, and the requested resource is being returned.
Redirection Messages (3xx): When a client encounters a redirection status code, it is informed that further action needs to be taken to complete the request. The most well-known code in this class is 301 (Moved Permanently), which indicates that the requested resource has been permanently moved to a new URL.
Client Error Responses (4xx): These codes are sent by the server when the client has made an error in the request, such as requesting a non-existent resource or unauthorized access. You’ve probably encountered the 404 (Not Found) code, which is displayed when a requested resource does not exist.
Server Error Responses (5xx): When the server encounters an error while processing the request, it returns a status code from the 5xx class. The 500 (Internal Server Error) code is a common example, indicating that something went wrong on the server’s side, and it couldn’t fulfill the request.
Now, let’s dive into the comprehensive list of HTTP response status codes:
| Status Code | Category | Meaning | Common Use Cases |
| 100 | Informational Responses | Continue | Rarely encountered, server awaits client continuation |
| 101 | Informational Responses | Switching Protocols | Server switches protocols, e.g., from HTTP to WebSocket |
| 200 | Successful Responses | OK | Standard response for successful requests |
| 201 | Successful Responses | Created | Indicates the creation of a new resource |
| 202 | Successful Responses | Accepted | Request accepted for processing but not completed |
| 204 | Successful Responses | No Content | Successful request with no response body |
| 206 | Successful Responses | Partial Content | Used for partial GET requests |
| 300 | Redirection Messages | Multiple Choices | Offers multiple options for the resource |
| 301 | Redirection Messages | Moved Permanently | Indicates permanent relocation of the resource |
| 302 | Redirection Messages | Found | Temporary redirection to a different URL |
| 304 | Redirection Messages | Not Modified | Informs client that cached resource is still valid |
| 307 | Redirection Messages | Temporary Redirect | Temporary redirection, original URL should be used |
| 308 | Redirection Messages | Permanent Redirect | Permanent redirection to a new URL |
| 400 | Client Error Responses | Bad Request | Server can’t understand due to malformed syntax |
| 401 | Client Error Responses | Unauthorized | Authentication required, valid credentials needed |
| 403 | Client Error Responses | Forbidden | Client lacks permission to access the resource |
| 404 | Client Error Responses | Not Found | Requested resource doesn’t exist |
| 405 | Client Error Responses | Method Not Allowed | HTTP method used is not allowed for the resource |
| 408 | Client Error Responses | Request Timeout | The server timed out while waiting for the client’s request. |
| 429 | Client Error Responses | Too Many Requests | Client exceeded request rate limits |
| 500 | Server Error Responses | Internal Server Error | General server error, something went wrong on the server |
| 502 | Server Error Responses | Bad Gateway | Proxy or gateway received an invalid response from upstream |
| 503 | Server Error Responses | Service Unavailable | Server temporarily unable to handle the request |
| 504 | Server Error Responses | Gateway Timeout | Proxy or gateway didn’t receive a timely response |
Common Use Cases for HTTP Response Status Codes
Now that we’ve covered the comprehensive list of HTTP response status codes, let’s explore some common scenarios where these codes come into play:
200 (OK): This is the standard response to successful HTTP queries. It’s used when the server successfully delivers the requested resource, whether it’s a web page, image, or data.
301 (Moved Permanently): When a website undergoes a redesign or restructuring, this status code is used to inform search engines and browsers that the old URL has permanently moved to a new one. It helps preserve search engine rankings and user experience.
404 (Not Found): Perhaps the most recognizable status code, 404 is displayed when a requested resource is not found on the server. This can occur due to typos in URLs or when a page has been removed.
403 (Forbidden): When a user tries to access a resource they don’t have permission to view, such as a protected admin page, the server responds with a 403 status code.
502 (Bad Gateway): This code often appears in scenarios where a proxy server or gateway is involved, and the upstream server fails to provide a valid response. It’s a sign of potential network issues.
503 (Service Unavailable): When a server is temporarily overwhelmed due to high traffic or maintenance, it returns a 503 status code. This informs clients that the server is currently unavailable but should be back soon.
Conclusion
HTTP response status codes are a crucial aspect of web development and the browsing experience. They provide a standardized way for servers to communicate with clients, informing them of the outcome of their requests. Understanding these codes is essential for web developers, system administrators, and anyone involved in troubleshooting website issues.
In this article, we’ve provided you with a comprehensive list of HTTP response status codes, categorized by their classes, and explained their meanings and common use cases. The next time you encounter a 404 error or wonder why a website is temporarily unavailable, you’ll have a better understanding of the HTTP response status codes at play.