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What are HTTP Response Codes? Here’s a List With An Explanation of Each

HTTP response codes, also known as HTTP status codes or header response codes, are a set of three-digit numeric codes returned by a web server in response to an HTTP request made by a client (usually a web browser or another application). These status codes are included in the response headers of an HTTP response to provide information about the outcome of the request. They serve several important purposes:

  1. Communication: HTTP response codes allow the webserver to communicate the result of a client’s request back to the client in a standardized way. This communication is essential for understanding whether the request was successful or encountered an issue.
  2. Error Handling: They help in error handling and debugging. When a request fails or encounters an issue, the status code explains what went wrong. This information is valuable for developers and administrators to identify and fix problems.
  3. Redirection: HTTP response codes like 301 (Moved Permanently) and 302 (Found) are used for redirection. They inform the client that the requested resource has been moved to a different URL. This is important for maintaining web page links and SEO.
  4. Caching: Some status codes, such as 304 (Not Modified), help in caching. If a client has previously requested a resource that hasn’t changed, the server can respond with a 304 status code, indicating that the client can use its cached copy, reducing server load and improving performance.
  5. Security: Certain status codes, like 401 (Unauthorized) and 403 (Forbidden), are used to enforce security measures. They indicate the client lacks proper authentication or authorization to access the requested resource.
  6. Resource Availability: Status codes like 404 (Not Found) or 410 (Removed) signify that the requested resource does not exist on the server. This is helpful for users and search engines to understand that the content they are looking for is unavailable.
  7. Performance Optimization: HTTP status codes can help optimize performance. For example, a 503 (Service Unavailable) status code informs the client that the server is currently overloaded or undergoing maintenance, prompting the client to try again later.
  8. Compatibility: They ensure compatibility and interoperability between web clients (browsers, mobile apps, etc.) and web servers. All parties can interpret and act upon status codes in a standardized way.

HTTP Response Code Classifications

HTTP response status codes are divided into five classes, each representing a different category of response:

  • 1xx Informational response – The request has been received, and the server is continuing to process the request.
  • 2xx Successful response – The request has been successfully processed, and the server is returning the requested information to the client.
  • 3xx Redirection response – The requested resource has been moved or is temporarily unavailable, and the server redirects the client to a new URL or resource.
  • 4xx Client error response – The request contains incorrect syntax or cannot be fulfilled, and the server cannot process the request.
  • 5xx Server error response – The server cannot fulfill the request due to an error on the server side.

HTTP Response Codes List

100ContinueThe initial part of the request has been received, and the client should continue with the request.
101Switching ProtocolsThe server is switching protocols as requested by the client.
200OKThe request was successful, and the server has returned the requested data.
201CreatedThe request has been fulfilled, and a new resource has been created as a result.
202AcceptedThe request has been accepted for processing but is not yet complete.
204No ContentThe server successfully processed the request but does not need to return a response body.
206Partial ContentThe server is delivering only part of the resource due to a range request.
300Multiple ChoicesThe request has multiple possible responses, and the client should choose one.
301Moved PermanentlyThe requested resource has been moved permanently to a new URL.
302FoundThe requested resource has been temporarily moved to a new URL.
303See OtherThe response to the request can be found under a different URL.
304Not ModifiedThe resource has not been modified since the last request.
307Temporary RedirectThe request should be repeated with another URL, but the same method should be used.
308Permanent RedirectThe request and all future requests should be repeated using another URL.
400Bad RequestThe server cannot understand the request, possibly because of incorrect syntax.
401UnauthorizedThe client does not have the necessary authorization to access the requested resource.
402Payment RequiredReserved for future use. Originally intended for digital payment systems.
403ForbiddenThe client does not have permission to access the requested resource.
404Not FoundThe requested resource does not exist on the server.
405Method Not AllowedThe request method is not supported for the requested resource.
406Not AcceptableThe server cannot produce a response matching the list of acceptable values defined in the request’s headers.
407Proxy Authentication RequiredThe client must first authenticate itself with the proxy.
408Request TimeoutThe server timed out while waiting for the request.
409ConflictIndicates that the request could not be completed due to a conflict with the current state of the target resource.
410GoneThe requested resource is no longer available and will not be available again.
411Length RequiredThe server requires a valid Content-Length header to be provided in the request.
412Precondition FailedOne or more conditions specified in the request header fields evaluated to false.
413Payload Too LargeThe server refuses to process the request because the payload is too large.
414URI Too LongThe server refuses to process the request because the URL is too long.
415Unsupported Media TypeThe server refuses to accept the request because the payload format is unsupported.
416Range Not SatisfiableThe server cannot satisfy the range request specified in the request’s Range header field.
417Expectation FailedThe server cannot meet the requirements of the Expect request-header field.
418I’m a teapotThis code was defined as an April Fools’ joke and is not expected to be implemented.
429Too Many RequestsThe user has sent too many requests in a given amount of time.
500Internal Server ErrorThe server encountered an error while processing the request.
501Not ImplementedThe server does not support the functionality required to fulfill the request.
502Bad GatewayThe server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed.
503Service UnavailableThe server is currently unable to handle the request due to temporary overloading or maintenance of the server.
504Gateway TimeoutThe server, while acting as a gateway or proxy, did not receive a timely response from the upstream server or application.
505HTTP Version Not SupportedThe server does not support the HTTP protocol version used in the request.
507Insufficient StorageThe server is unable to store the representation needed to complete the request.
511Network Authentication RequiredThe client must authenticate itself to get the requested response.
599Network Connect Timeout ErrorThis status code is not specified in any RFC but is used by some HTTP proxies to signal a network connect timeout error.

How To View An HTTP Response Code

The HTTP status code is a separate piece of information provided in the response headers when you request an HTTP to a web server. You can not see it in the output HTML displayed in a browser. To view the HTTP status code in Chrome Developer Tools, you would need to do the following:

  1. Open Chrome Developer Tools: Follow the steps mentioned earlier to open Chrome Developer Tools using Ctrl + Shift + I.
  2. Network Tab: In the Developer Tools panel, navigate to the Network tab.
  3. Make a Request: Visit the web page or trigger the specific HTTP request you want to inspect. You will see network requests listed in the Network tab as they are made.
  4. Select the Request: Click on the specific network request corresponding to the page or resource you’re interested in. This will display detailed information about the request and response in the right panel.
  5. View Response Headers: In the right panel, go to the “Headers” tab. The HTTP response headers are displayed here, including the HTTP status code.

The HTTP status code will be listed in the response headers as Status Code with a brief description. For example, you might see 200 OK for a successful request, 404 Not Found for a resource that doesn’t exist, or 500 Internal Server Error for a server-side error.

HTTP response codes are a vital part of the HTTP protocol, providing a standardized and efficient means of communication between clients and servers, aiding in error handling, security, redirection, and overall web performance. They are essential for a well-functioning and reliable web ecosystem.

Douglas Karr

Douglas Karr is the founder of the Martech Zone and CEO of DK New Media. Douglas has helped dozens of successful MarTech startups, has assisted in the due diligence of over $5 bil in Martech acquisitions and investments, and continues to assist companies in implementing and automating their sales and marketing strategies. Douglas is an internationally recognized digital transformation and MarTech expert and speaker. Douglas is also a published author of a Dummie's guide and a business leadership book.

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