How to Fix Proxy Error Codes?

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Web scraping, web crawling, and similar methods are used by companies and individuals in order to gather information. Public data collected in such a way might be useful for further business activities. To do it efficiently, one often needs to use a third-party security tool – a proxy server. Otherwise, there is a high risk of being denied access due to geo-blocks, getting banned due to too many requests from the same IP, or having other restrictions implemented by the website owners.

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While proxies help to go around all these, they also might fail in getting the wanted response. Such failure is known as a proxy error and, if that happens, you will see an error code describing its cause. In this article, we will look closer at the meanings of different proxy error codes and how to overcome these errors.

What is a proxy error?

A proxy error is a failure to receive the requested response from a server when using a proxy. In the client-server network, the cause of proxy errors can be both on the client and the server side, depending on whether it is the end server or a proxy.


A common cause for client-side proxy errors is a bad internet connection. Also, it might be that it was an incorrectly configured bad request, that the proxy or the end-server cannot understand and parse.


On the server end, it might be that the content has been moved or no longer exists which is causing the proxy error. Furthermore, it might be that private content is being requested, which means that additional authentication by the user or proxy is required. Finally, there may also be temporary issues like maintenance or server downtime.


The proxy server might also be causing issues for similar reasons. This might mean that in order to continue using the proxy, the windows registry or proxy settings need to be changed.


In any case, when the result is a proxy error, you will get an error message and a Hypertext Transfer Protocol (HTTP) status code that defines the type of the error. Understanding what these error codes mean will help to find the solution for HTTP proxy errors, whatever their cause would be.

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Classification of the HTTP status codes

Let’s start with the way HTTP status codes are classified which will immediately help differentiate among them. There are 5 classes of such codes, indicating different types of responses to the HTTP request and with 100 numerical values reserved for each class.


The classes are defined with the recent updates in the Internet Engineering Task Force (IETF) publication RFC 7231. They are as follows.

Informational responses (100-199)

The first set of codes consists of informational responses that are meant to inform about the status of the request before it is completed. For example, error code 100 “Continue” is returned in case the request is not completed to let the user know that it should be continued until fruition. Similarly, other codes in this section inform the user that the request is being processed in order to avoid being cut off too early on the client-side.

Successful responses (200-299)

This is the set of HTTP messages indicating that the request has been processed and returned successfully. However, only code 200 “OK” truly means an unambiguously successful result. Other responses have an implicit “but” attached to them, which can mean a rather paradoxical situation of successful code. 


For example, error code 204 “No content” indicates that the headers might be useful but there is no content for the specific request made. And error code 203 ”Non-authoritative information” means that the request was fulfilled but a local or third-party copy was used instead of the original resource.

Redirection messages (300-399)

These messages inform you that the request should be directed differently to get the resource. In this case, there might be enough information for the user agent to redirect automatically or there is an issue that prevents redirection. 


For example, error code 300 “Multiple choice” indicates that there are multiple resources that could fulfill the request, but no standardized way to choose among them. If links are provided with this message, the user can choose manually. Whereas error code 307 “Temporary redirect” means that the client can find the same resource at a different URI but using the same HTTP method

Client error responses (400-499)

This is the set of errors that are perceived by the web server to originate on the client-side. As bad requests are presumed to be the primary cause of these responses, most of the common proxy errors are in this group. Thus, examples are discussed in more detail in the following section.

Server error responses (500-599)

This group also defines some of the usual proxy errors as there can be issues with proxy servers acting as gateways to the end-server. Usually, server error responses indicate that something is wrong either with the end server or the proxy server. The common examples of the latter are talked about in the following part of this article.

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Most common proxy error codes

There are many error codes from the 5 classes described above that in certain circumstances could signify proxy errors. However, some are more common than others. 

Error code 305 - Use proxy

It means that to access the content, your request should be redirected through a proxy server. If you believe to be using a proxy, this might mean that something is not right with the proxy settings and a proxy override could be necessary. It should be noted that some web browsers, including Mozilla, no longer use this proxy error code due to security reasons.

Error code 306 - Switch proxy

Also no longer used by Mozzila, this error code means that for the following request you should use a different proxy, specified by the error message.

Error code 400 - Bad request

This is a generic client error code returned when something is wrong with the request but the server is not able to specify it. When the proxy server or the end receiver cannot correctly read or parse the request it is deemed that something is wrong with the syntax or framing of the request, or that there is a deceptive request routing. 


In the latter case, you should check the header of the request as something about it makes it unreadable or suspicious to the server.

Error code 403 - Forbidden

It means that the server received the request, understood it, and it was denied in order to protect private content. The web server recognizes the client as someone that does not have permission to access information on this resource. As the IP address is what allows the server to recognize the client, it might mean that the content is forbidden due to the particular proxy IP used.

Error code 407 - Proxy authentication required

This error code is returned by the proxy when it is missing some form of required proxy authentication or credentials from your side. It might mean that certain IP addresses are not whitelisted with the proxy. In such a case IP settings need to be updated, credentials provided, or IPs whitelisted.

Error code 408 - Request timeout

Some servers send this response when the connection is idle and the server would like to shut it down. Additionally, it can sometimes mean that the server did not respond within a set timeframe.  In case of receiving such an error code, check the load created on your web server. Connectivity problems could also be causing this issue.

Error code 417 - Expectation failed

This error code means that the server cannot fulfill the request issued under the “expect” header. A proxy server that has evidence pointing to the end server’s inability to fulfill this request would also issue such an error message.

Error code 429 - Too many requests

Sometimes, the web server applies rate limiting to protect itself from malicious attacks or overload. Error code 429 is issued when too many requests within the specified time frame have been sent. It can be solved by using a rotating proxy as this would keep changing IP requests either with every request or after a specified interval of time.

Error code 500 - Internal server

It’s a generic response for when the server or the proxy has encountered a problem it does not understand or know how to fix.

Error code 502 - Bad gateway

This error code indicates that the server was working as a gateway or a proxy and received an invalid response from an upend server.

Error code 503 - Service unavailable

Usually, this code is received when the server is under temporary maintenance or is overloaded and therefore cannot handle another request at the moment. However, when using a proxy server this might mean that your proxy IP has been identified and the client agent is unable to solve the captcha.

Error code 504 - Gateway timeout

Error code 504 is issued when the server is acting as a gateway or a proxy and does not receive a response from a server higher up the chain within a specified time frame.

Fixing proxy error codes

As you’ve probably gathered, even for specific error codes there is more than one possible cause. So, a few possible solutions should be checked whenever proxy errors are encountered. Here are some basic solutions you can try when dealing with proxy errors.


  • As many HTTP proxy errors are identified as client errors, you should check if everything is alright on your side as much as possible. This means checking your request for any errors in syntax. You might also need to change your HTTP filter settings to ensure that the HTTP filter component is configured correctly. Additionally, it is always worth checking if everything is alright with your internet connection.
  • Check if any other program is causing hindrances with your proxy connection. This might be your antivirus, so pausing some of its features or the entire program might help. Additionally, try using a different web browser and see if that helps. You may also try defaulting to the original proxy settings as determined by your proxy provider.
  • As a lot of proxy errors are caused by the proxy IP being blocked due to too many requests, you can decrease the number of requests you send within a time interval. To do this automatically, switch to rotating proxies. If the problem does not seem to be persistent, you may just manually abandon the blocked proxy and use another proxy IP.
  • Use a proxy manager. You can find such open-source software tools and use them for free. A proxy manager can help you to avoid HTTP errors by automatically managing your proxies and solving some of the issues they may encounter. 
  • If none of the above works but you are pretty convinced that the root cause of the issue lies within the proxy server the last option you have is to contact your proxy provider. They might be able to solve the issue on their side or advise you on how to proceed.

Summing up

Getting an HTTP error code is really annoying as it means that your work is delayed or completely halted. However, understanding what the codes actually mean is the first step toward fixing the problem. 


Of course, it’s not always you or your proxy server, sometimes it’s them – the end server. In this case, all you can do is wait until they fix the problem or abandon your request completely. But other than that, when dealing with proxy errors there’s something you can do to try and fix them. Hopefully, the proposed guidelines above will help you find your way to the solution.

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