What is the Website’s 404 Error?

Today we will learn HTTP errors, you will know what 404 errors are. In fact, there are almost a hundred different error codes. Don’t worry, you don’t have to memorize all of them, but there are techniques to figure out roughly where the error is coming from.

Why 404 error?

Why invent these numbers?

But why do we invent these error numbers? The answer is actually quite simple, when a user visits a website through his browser, the browser sends a request to the server according to the HTTP protocol. The server will also respond in HTTP format and if all goes well will send the requested resources (in our case the web page). But things get more complicated when there are errors. It’s good to know that there’s an error, but it’s better to know where the error is. This is why error numbers are quickly assigned to different types of errors. This is much more practical and saves many developers time. For example, an error starting with 5 is a server level problem.

There are five types of errors


2. Success

3. Redirects

4. User error

5. Server Error

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So if the error number starts with 4, we know that the problem is from the user.

Why 404 error?

But why 404 error? The first number is 4, which is the error coming directly from the user and not from the server. Indeed, the 404 error means that the resource was not found, the server searched for the user but couldn’t find it, so the error came from the user who did not provide the correct url.

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Discover 418 . error

The HTTP 418 error has nothing to do with other errors. Indeed its meaning is “I am a teapot”. It has actually been a joke since it first appeared in RFC 2324 on April 1, 1998. The explanations given by the developers are: “There is coffee everywhere in the world. . Increasingly, in a world where computers are ubiquitous, people want to make coffee. Brewing coffee is an art, but the distributed wisdom of the web-connected world surpasses art. Thus, there is a strong, rich demand for a clearly designed protocol for brewing coffee. Coffee is brewed using a coffee pot. Networked coffee makers require control protocols if they want to be controlled.”

In other words, Hypertext Coffee Pot Control Protocol, or HTCPCP, is intended to send an error back to everyone who wants to control the coffee pot remotely, telling them they’ve mistaken their address for… tea.

This April 1st “joke” became famous at the time, and its error code remained the same.

There are still people questioning this 418 error, even today.

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Other HTTP Errors

For those who want to find a specific error, you can refer to the error tables categorized by category below.

Some of the code is still unused, but will be used in the future. The other codes don’t lead to any specific impressions to the user, but are still understandable (e.g. codes 200 or 304, which the client never sees because they’re involved in the vast majority of successful requests. ).

All major HTTP errors are presented in these tables, of different error types:

Codes starting with 1 (Info):

Code Message Meaning
100 tiếp tục Waiting to be processed.
101 Switching Protocols Accept the protocol change.
102 Processing In progress (avoiding the client to exceed the waiting period).
103 Early Hints While waiting for the final response, the server returns links where the client can start downloading.

Codes starting with 2 (Success):

Code Message Meaning
200 OK The request was processed successfully. The response will depend on the query method used.
201 Created The request was processed successfully and the document was created.
202 Accepted The request is processed, but the outcome is not guaranteed.
203 Non-Authoritative Information Information returned, but generated by an uncertified source.
204 No Content The request was processed successfully, but there is no information to return.
205 Reset Content The request is processed successfully, the current page can be deleted.
206 Partial Content Only part of the resource has been transmitted.
207 Multi-Status Many answers. (WebDav)
208 Already Reported Previous material has been deposited in this collection. (WebDav)
210 Content Different The client-side copy of the resource is different from the server-side copy (content or property). (WebDav)
226 IM Used The server completed the resource request, and the response is the representation of the result of one or more operations applied to the current result.

Codes starting with 3 (Redirect):

Code Message Meaning
300 Multiple Choices The requested URI refers to some resource.
301 Moved Permanently The document has been moved permanently.
302 Found Document has been moved temporarily.
303 See Other The answer to this request lies elsewhere.
304 Not Modified The document has not been modified since the last request.
305 Use Proxy (since HTTP/1.1) The request must be routed to the proxy.
306 Switch Proxy Code used by older version of RFC 26167, now reserved. It means “Following requests must use the specified proxy”.
307 Temporary Redirect The request must be temporarily redirected to the specified URI.
308 Permanent Redirect The request must be permanently redirected to the specified URI.
310 Too many Redirects The request must be redirected too many times or fall victim to a redirect loop.

Codes starting with 4 (web client error):

Code Message Meaning
400 Bad Request The query syntax is wrong.
401 Unauthorized Authentication is required to access the resource.
402 Payment Required Payment is required to access resources.
403 Forbidden The server understood the request, but refused to fulfill it. Unlike 401 errors, validation won’t make any difference. On servers that require authentication, this usually means that the authentication has been accepted, but the access permission does not allow the client to access the resource.
404 Not Found Resource not found.
405 Method Not Allowed Unauthorized query method.
406 Not Acceptable The requested resource is not available in a format that complies with the “Accept” header of the request.
407 Proxy Authentication Required Access to the resource is allowed by identity with the proxy.
408 Request Time-out The amount of time the request from the client has been waiting on the server side. According to the HTTP specification: “The client does not make a request while the server is ready to wait. The client MAY repeat the request without modification at any time afterwards.”
409 Conflict The request could not be processed at this time.
410 Gone The resource is no longer available and the redirect address is unknown.
411 Length Required The length of the request is not specified.
412 Precondition Failed The precondition sent by the request is not checked.
413 Request Entity Too Large The requirement is too high.
414 Request-URI Too Long URI is too long.
415 Unsupported Media Type The query format is not supported for a certain method and resource.
416 Requested range unsatisfiable The “scope” query header fields are incorrect.
417 Expectation failed The behavior that is expected and defined in the header of the request is not satisfied.
418 I’m a teapot “I am a teapot”: This code is defined in RFC 232410 of April 1, 1998, Hyper Text Coffee Pot Control Protocol. It’s a prank by webmasters, intended to send a bug back to anyone who wants to remotely control a coffee pot, telling them they misplaced a teapot
421 Bad mapping / Misdirected Request The request was sent to a server that was not able to generate a response (e.g. because the connection was reused).
422 Unprocessable entity Entity provided with an incomprehensible or incomplete request. (WebDAV)
423 Locked The operation cannot take place because the resource is locked. (WebDAV)
424 Method failure A method in the transaction failed. (WebDAV)
425 Too Early The server cannot process the request because it can be replayed.
426 Upgrade Required The client should change the protocol, e.g. to TLS/1.0.
428 Precondition Required Requirements must be conditional.
429 Too Many Requests The client made too many requests within a certain time frame.
431 Request Header Fields Too Large The HTTP headers sent exceed the maximum size allowed by the server.
449 Retry With Code defined by Microsoft. The request must be returned after performing an action.
450 Blocked by Windows Parental Controls Microsoft Code. This error occurs when Windows Parental Controls is enabled and blocks access to the page.
451 Unavailable For Legal Reasons This error code indicates that the requested resource cannot be accessed for legal reasons.
456 Unrecoverable Error Unrecoverable error. (WebDAV)

Codes starting with 5 (Server Error):

Code Message Meaning
500 Internal Server Error

Internal server error.

501 Not Implemented The requested function is not supported by the server.
502 Bad Gateway ou Proxy Error By acting as a proxy or gateway server, the server receives an invalid response from the remote server.
503 Service Unavailable The service is temporarily unavailable or under maintenance.
504 Gateway Time-out Response timeout from server to intermediate server.
505 HTTP Version not supported The HTTP version is not supported by the server.
506 Variant Also Negotiates Negotiation error.
507 Insufficient storage Not enough space to edit properties or build collections. (WebDAV)
508 Loop detected Loop in a resource link. (WebDAV)
509 Bandwidth Limit Exceeded Used by many servers to indicate over limit.
510 Not extended The request does not respect the extended HTTP resource access policy.
511 Network authentication required The client must authenticate to access the network. Used by fixed gateways to redirect clients to the authentication page.

Also, if you have any questions, please comment below. You can also see more mistakes to avoid when designing a website here.

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