4xx Status Code Meanings and Roles

Published: Alex Shashenko 2024-01-29 all articles | Glossary | FAQ

Everyone who's been browsing the Internet frequently at least once in a lifetime has encountered the situation when there’s a technical message instead of an expected web page. This is a notification about the present status of the webpage, and it includes valuable info that briefly explains what’s happened with this webpage. Under most conditions, to users it’s literally just a notifier that says that the webpage is inaccessible one way or another. On the other hand, for webmasters it’s a sign that something’s either processing or needs to be fixed.

In usual circumstances, such a notifier either vanishes when you reload the webpage, or keeps showing up because something’s happened. Namely, status code 400 emergence is meaning that the webpage’s URL was typed incorrectly. And the entire set of notifiers it belongs to, or 4xx codes, is ordinarily about various situations whenever the request was dispatched incorrectly and there was no proper response. 

Although for webmasters it’s routinely the minor server-side failure, there are situations when those types of troubles need fast diagnosing to be pinpointed and solved quickly by the webmasters. That’s why it’s vital to obtain the knowledge about varieties of HTTP notifiers and 4xx in particular, or, at the minimum, to be acquainted with places where to get a thorough explanation.

400 status code group in a nutshell

400 status code group

To get a thorough understanding of 400-499 notifiers, webmasters firstly need to get more info about all HTTP coded messages at least in a general sense. Because this particular set of notifiers is only one among five others, and all of those sets are distinguishable by their own features, situations of appliance and included errors. 

Almost all info about them, literally, is stored in the MDN database by Mozilla or in the RFC 2616 made by IETF, the team that manages literally all such codes. But you don’t need to study them thoroughly if you’re a novice and you want to be acquainted with those notifier groups without going too deep into the topic.

  • The 1xx notifier group is about the prolongation of the data loading - such messages mean that all is mostly fine, but something needs too much time to finish. It is usually visible only for webmasters.

  • The 2xx code category is typically unseen by users, and it notifies about usual circumstances whenever the server operates without any troubles on any level.

  • The 3xx notifiers are all about redirects. It includes all sorts of notifiers when the server needs to respond by sending the user to another directory.

  • The 4xx notifications are basically messaging both to the user and to the webmaster that the client or the server has messed up something when trying to get to the webpage or other data. 

  • The 5xx codeset is about bad circumstances on the server, counting various things starting with connection problems and up to its bad configuration included.

As it was stated, the 4xx notifiers are all about user-side issues. Including the URL typos, lacking access rights or other things inhibiting the processing procedure’s successful completion. Like situations when the page is inaccessible or was erased.

Common 4xx codes and their meanings

Common 4xx codes

Being a rather large group, 4xx has a batch of various subcodes beginning from 400 and way to 499 status code. And although not all of them are filled in by the IETF, it still has a wide assortment of designated numbers for notifiers.

The most recurring and typically encountered notifier from this batch is, obviously, 404 - Not Found. This notifier with the 404 status code says that the webpage is inaccessible, hidden or non-existent. But it's not the sole code that's in this category - there is a big collection of them and they can even be vaguely grouped.

  • 401 - Unauthorized. The 401 status code is displayed if there was no proper authorization before visiting the site.

  • 403 - Forbidden. The status code 403 notifier appears if access rights are insufficient even after authentication.

  • 404 - Not Found. The 404 status code notifier defines that the request procedure is fetching improperly relocated, non-existent or hidden data.

  • 405 - Method Not Allowed. The 405 status code defines that the server is forbidding the utilized access procedure.

  • 406 - Not Acceptable. The 406 status code notifier is displayed when the demanded search or lookup procedure can’t be finished.

  • 407 - Proxy Authentication Required. The 407 status code notifier says that authorization on the proxy is needed.

  • 408 - Request Timeout. The 408 status code defines that something inhibits the network and causes critical slowdowns on one of the sides, and it makes the request too slow to continue.

  • 409 - Conflict. The 409 status code notifier occurs if there are mismatching or conflicting settings taking into account both sides of the user-server pair.

  • 410 - Gone. The 410 status code notifier says that the resource was irreversibly erased from the server.

  • 413 - Payload Too Large. The 413 status code notifier is utilized if the request incorporates too much data to handle.

  • 414 - URI Too Long. This status code 414 notifier emerges if the URI (usually, URL) has a larger number of characters than it’s possible to accept.

  • 415 - Unsupported Media Type. The 415 status code is a self-explanatory notifier defining that the uploaded image, audio or video has a non-supported format and operation won’t continue.

  • 422 - Unprocessable Entity. The 422 status code notifier encompasses that the request carries damaged info or there are server malfunctions that are interfering with the procedure completion.

  • 424 - Failed Dependency. This 424 status code notifier is displayed if the last request in the query malfunctions and the chained continuation of the next one is impossible.

  • 429 - Too Many Requests. The self-explanatory notifier incorporates the 429 status code if the number of tries to fetch the data from the server exceeds its predefined limitation.

  • 431 - Request Header Fields Too Large. The status code 431 notifier is displayed if a request embodies a too large header that’s impossible to handle under current settings.

  • 443 - SSL/TLS Handshake Failed. The 443 status code is displayed whenever there are conflicts with SSL or TLS certificates. including expiration and mismatched configuration.

  • 451 - Unavailable For Legal Reasons. The 451 status code is incorporated into a notifier only if the server is banned by the law in a certain area or in an individual country.

Additionally, there are rarely emerging notifiers like 417 status code, completely obsolete ones like 430 status code or even messages made for fun like 418 ‘I’m a Teapot’ notification that was created specifically for April Fools’ Day way back in 1998.

How can be a request failed with status code 400

how can be a request failed with status code 400

Almost all 4xx notifiers appear due to the activity of the user or the software, but sometimes it could be fixed only by the webmaster. And all causes for notifiers from the 4xx codeset are ordinarily typos, inaccuracies or, in instances of server-related troubles, badly configured settings. Therefore, although sometimes it may be the server-side fault, in general terms all 4xx notifications are about the fact that the resource or the content are inaccessible for some reason.

Taking server-related mishaps into account, it was mentioned earlier that there’s a possibility that its setup is messed up. Beginning from the wrong acceptable size of the headers or even wrongly set up requirements (417 error) and up to the lacking bandwidth or even expired SSL or TLS.

From SEO point of view, any search engine parsing service basically will exclude the site from the SERP queues as soon as any of the 4xx notifiers appear. Because, all things considered, they won’t be able to fetch and cache the site, therefore they’ll have nothing to parse and nothing to add to the SERP queues. And it’ll be followed by situations when the traffic on the site is reduced, and the site’s ratings start going down as if it suddenly became completely inaccessible.

The 400 response code importance

400 response code importance

For webmasters the appearance of 4xx notifications in logs or for users conveys that there’s a huge possibility that the situation will become bad if it won’t be diagnosed and fixed. On top of it, it conventionally means that something on the server was set up wrong during initial configuration or last update. To put the case in point, 404 or 410 are saying that the demanded object was moved or erased permanently without any redirection. Or if the server returned 409, then its configuration could be incorrect.

Also, as it was mentioned above, 4xx notifiers appearing for users are basically the signal for any webmaster to fix things as swiftly as possible to prevent problems for SEO of the site and its current SERP ratings. It could be hard for the team to return to the preceding positions in queues if the situation with 4xx messages is unnoticed or unfixed for a long time. Because it will basically be the same as when the site is inaccessible and could not be loaded completely despite being in working condition.

Moreover, considering all that was mentioned above, 4xx issues will surely affect the user experience in a bad way. Because if the issue is on the client’s side, then it won’t disappear no matter what the user will do. And if left unfixed, it will be a mishap of the same degree as it’s for SEO - users won’t be able to get to the site no matter how hard they try.

How to fix the response code 400

how to fix the response code 400

The best method to tackle the appearance of 4xx notifiers is to monitor the site with powerful tools in addition to constantly looking through the server logs. To put the case in point, any webmaster could use automated monitoring services offered by the Host-Tracker platform. Particularly, it has a convenient HTTP monitoring tool that will check the returned notifiers with codes from various places around the world. 

Taking into account that this tool is working as a client, Host-Tracker toolkit can reproduce basically any 4xx return except ones related to user-side problems. And what’s most important, round-the-world access points can even find out the appearance of the 451 notifier for locations and the site’s state as prohibited by the law there along with it.

Resolving most of the mishaps linked to this group of notifications is not too troublesome for webmasters by any means. Because all of them are tied to the accessibility on the server, one way or another. Therefore, whether the data was moved or erased, the setup of the header reactions were misconfigured, the current SSL/TLS certificate has expired, or any other associated thing happened, the notifier itself will point in the right direction and the webmaster will only need to reconfigure the source of the trouble to resolve it. 

But settling the trouble is not the sole problem here when it comes to the user-side. Preparing and adjusting notification messages for users is also essential. And although the webmaster is not responsible for codes themselves, the notifiers are adjustable to be user-friendly and informative. But they shouldn’t be too long and burdening to read. Instead, they should be displayed as technical, short and understandable for anyone without them being tech-savvy. And it can even contain redirects to accessible or useful web pages on the site.


All things considered, 4xx notifiers with HTTP codes and info about them are essential for all aspects of the site. Be it maintenance procedures, site stability, SERP ranking or user experience - all of them could be affected by the appearance of almost any code from the group. Taking this into account, it is highly vital to keep such occurrences in check by all means. And the best method to do it is to keep the site under constant monitoring with the help of powerful tools like Host-Tracker platform that has methods to find any of the server-side 4xx notifiers as soon as the problem happens.


What is status code 400?

Basically, this notifier says about a typo or wrongly entered address of the webpage. 

What is status code 404?

This message appears whenever the webpage is inaccessible or hidden.

What is status code 401?

This 4xx notification says that the login into account with access rights is needed to continue.

What is status code 403?

This notifier is like 401, but says that access rights are insufficient even after authentication.

What is status code 429?

This particular message says that too many tries to access the webpage were made and therefore they won’t be finished.

List of references to official HTTP documentation and webmaster resources

1. Official HTTP Documentation:

Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., & Berners-Lee, T. (1999). Hypertext Transfer Protocol -- HTTP/1.1. IETF. RFC 2616. https://tools.ietf.org/html/rfc2616

Nottingham, M., & Fielding, R. (2020). HTTP Semantics. IETF. https://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html

2. Webmaster and Developer Guides:

Mozilla Developer Network (MDN) Web Docs. HTTP response status codes. https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

Google Webmasters. Google Search Central: HTTP status codes. https://developers.google.com/webmaster-tools/v1/errors?hl=en

3. Error Monitoring and Resolution Tools:

Google Search Console Help. Crawl Errors report (websites). https://support.google.com/webmasters/answer/35120?hl=en

Host-Tracker. Website Performance Monitoring. https://www.host-tracker.com/en

Tags: usecase

About author

Oleksii Shashenko
Chief Communications and Technology Officer of HostTracker. Alex has been part of the team since the company's early days. His work focuses on business reporting, analysis of database statistics, and system administration. Alex also takes care of communication with the development team and clients.