The server can not find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 Forbidden to hide the existence of a resource from an unauthorized client. This response code is probably the most well known due to its frequent occurrence on the web.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/404

The request succeeded. The result meaning of "success" depends on the HTTP method:

GET: The resource has been fetched and transmitted in the message body.
HEAD: The representation headers are included in the response without any message body.
PUT or POST: The resource describing the result of the action is transmitted in the message body.
TRACE: The message body contains the request message as received by the server.

https://www.youtube.com/watch?v=6dP8ZUiY0xo

The request succeeded, and a new resource was created as a result. This is typically the response sent after POST requests, or some PUT requests.

https://www.youtube.com/watch?v=wJa5CTIFj7U

The request has been received but not yet acted upon. It is noncommittal, since there is no way in HTTP to later send an asynchronous response indicating the outcome of the request. It is intended for cases where another process or server handles the request, or for batch processing.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=wJa5CTIFj7U

This response code means the returned metadata is not exactly the same as is available from the origin server, but is collected from a local or a third-party copy. This is mostly used for mirrors or backups of another resource. Except for that specific case, the 200 OK response is preferred to this status.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=wJa5CTIFj7U

There is no content to send for this request, but the headers may be useful. The user agent may update its cached headers for this resource with the new ones.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=wJa5CTIFj7U

Tells the user agent to reset the document which sent this request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=wJa5CTIFj7U

This response code is used when the Range header is sent from the client to request only part of a resource.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=MykhXk6E4No

https://www.youtube.com/watch?v=wJa5CTIFj7U

The request has more than one possible response. The user agent or user should choose one of them. (There is no standardized way of choosing one of the responses, but HTML links to the possibilities are recommended so the user can pick.)

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=wJa5CTIFj7U

The request has more than one possible response. The user agent or user should choose one of them. (There is no standardized way of choosing one of the responses, but HTML links to the possibilities are recommended so the user can pick.)

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=-xsVfF2qBl0

https://www.youtube.com/watch?v=wJa5CTIFj7U

This response code means that the URI of requested resource has been changed temporarily. Further changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=El6vGfKr5L4

This is used for caching purposes. It tells the client that the response has not been modified, so the client can continue to use the same cached version of the response.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

https://www.youtube.com/watch?v=0QHmHR55_Lo

The server sends this response to direct the client to get the requested resource at another URI with same method that was used in the prior request. This has the same semantics as the 302 Found HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must be used in the second request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/307

https://www.youtube.com/watch?v=SYXcB83lLaM

This means that the resource is now permanently located at another URI, specified by the Location: HTTP Response header. This has the same semantics as the 301 Moved Permanently HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must be used in the second request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/308

https://www.youtube.com/watch?v=Ar7B9xuJFXA

The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/400

https://www.youtube.com/watch?v=BUELHFXmuOc

Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/401

https://www.youtube.com/watch?v=KqyOJv7JAn0

This response code is reserved for future use. The initial aim for creating this code was using it for digital payment systems, however this status code is used very rarely and no standard convention exists.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/402

The HTTP 403 Forbidden response status code indicates that the server understands the request but refuses to authorize it.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/403

https://www.youtube.com/watch?v=wM-dCR1ScE0

The request method is known by the server but is not supported by the target resource. For example, an API may not allow calling DELETE to remove a resource.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/405

The HyperText Transfer Protocol (HTTP) 406 Not Acceptable client error response code indicates that the server cannot produce a response matching the list of acceptable values defined in the request's proactive content negotiation headers, and that the server is unwilling to supply a default representation.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/406

This is similar to 401 Unauthorized but authentication is needed to be done by a proxy.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/407

This response is sent on an idle connection by some servers, even without any previous request by the client. It means that the server would like to shut down this unused connection. This response is used much more since some browsers, like Chrome, Firefox 27+, or IE9, use HTTP pre-connection mechanisms to speed up surfing. Also note that some servers merely shut down the connection without sending this message.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/408

https://www.youtube.com/watch?v=uz6RbpW6pv8

This response is sent when a request conflicts with the current state of the server.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/409

https://www.youtube.com/watch?v=YqMIOg3LS6E

This response is sent when the requested content has been permanently deleted from server, with no forwarding address. Clients are expected to remove their caches and links to the resource. The HTTP specification intends this status code to be used for "limited-time, promotional services". APIs should not feel compelled to indicate resources that have been deleted with this status code.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/410

https://www.youtube.com/watch?v=lXv2nprbd0g

Server rejected the request because the Content-Length header field is not defined and the server requires it.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/411

The HyperText Transfer Protocol (HTTP) 412 Precondition Failed client error response code indicates that access to the target resource has been denied. This happens with conditional requests on methods other than GET or HEAD when the condition defined by the If-Unmodified-Since or If-None-Match headers is not fulfilled. In that case, the request, usually an upload or a modification of a resource, cannot be made and this error response is sent back.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/412

Request entity is larger than limits defined by server. The server might close the connection or return an Retry-After header field.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/413

https://www.youtube.com/watch?v=GmvAgYza8xE

The URI requested by the client is longer than the server is willing to interpret.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/414

https://www.youtube.com/watch?v=HVrUE4RwUTM

The media format of the requested data is not supported by the server, so the server is rejecting the request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/415

https://www.youtube.com/watch?v=66UBxq46lxI

The HyperText Transfer Protocol (HTTP) 416 Range Not Satisfiable error response code indicates that a server cannot serve the requested ranges. The most likely reason is that the document doesn't contain such ranges, or that the Range header value, though syntactically correct, doesn't make sense.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/416

This response code means the expectation indicated by the Expect request header field cannot be met by the server.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/417

The request was well-formed but was unable to be followed due to semantic errors.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/422

Indicates that the server is unwilling to risk processing a request that might be replayed.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/425

The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server sends an Upgrade header in a 426 response to indicate the required protocol(s).

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/426

The origin server requires the request to be conditional. This response is intended to prevent the 'lost update' problem, where a client GETs a resource's state, modifies it and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/428

The user has sent too many requests in a given amount of time ("rate limiting").

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/429

https://www.youtube.com/watch?v=07IQAfhmWJU

The server is unwilling to process the request because its header fields are too large. The request may be resubmitted after reducing the size of the request header fields.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/431

The user agent requested a resource that cannot legally be provided, such as a web page censored by a government.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/451

https://www.youtube.com/watch?v=n9CsUK7B0X0

The server has encountered a situation it does not know how to handle.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/500

https://www.youtube.com/watch?v=i5iNqwKd3Lk

The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/501

This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/502

The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This response should be used for temporary conditions and the Retry-After HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/503

This error response is given when the server is acting as a gateway and cannot get a response in time.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/504

https://www.youtube.com/watch?v=Nm4yAlUikuw

The HTTP version used in the request is not supported by the server.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/505

The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper end point in the negotiation process.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/506

The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/507

The server detected an infinite loop while processing the request.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/508

Further extensions to the request are required for the server to fulfill it.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/510

The message "511 Network Authentication Required" typically indicates that the server you are trying to access requires authentication to continue. This means that you need to provide a valid username and password to gain access to the resource. The error code 511 is a HTTP status code that is defined in the HTTP/1.1 specification as "Network Authentication Required." This error code is typically returned by a web server when it requires a user to authenticate themselves before they can access the requested resource.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/511

(404) Not Found