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# Response Codes Basics

Posted on Jan 31, 2026

Five families of responses exist, namely:

• 1xx - these are called Informational Responses, they are normally hidden by the browser but they are important for websockets and streaming.
• 2xx - these are the successful responses.
• 3xx - these are called redirection messages
• 4xx - these are called client error responses, usually the client's fault
• 5xx - these are called server error responses
• You may get other codeds that are non-standard or custom to the server's software

## 1xx - Informational Responses

• 100 Continue

This is the interim response which indicate that the client should continue the request or ignore the response if the request is finished

• 101 Switching Protocols

This is the codee that is sent when an Upgrade request header from client indicates a switch in the protocol

• 102 Processing

This code indicates that the server is working on the request and does not have a response yet, but the client should not timeout or retry

• 103 Early Hints

Tries to tell the client "The final response is coming, but start preloading to save time"

## 2xx - Successful Responses

• 200 OK

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

• 201 Created

A new resource was created as a result, typically a response to POST or PUT requests

• 202 Accepted

The request has been received but not yet acted upon

• 203 Non-Authoritative Info

Response data is valid but it didn't come directly from the original server

• 204 No Content

The request succeeded, but there's nothing to send back beyond the headers

• 205 Reset

It tells the client to clear or reset the current view

• 206 Partial Content

The server is returning only a specific portion of the resource

## 3xx - Redirection Responses

• 300 Multiple Choices

there are several possible resources the client could use, and it must choose one

• 301 Moved Permanently

the requested resource has a new permanent URL and future requests should use it

• 302 Found

the requested resource is temporarily available at a different URL

• 303 See Other

the client should retrieve the result from another URL using a GET request

• 304 Not Modified

the cached version of the resource is still valid and no new content is sent

• 305 Use Proxy

the request must be made through a specific proxy, which is now largely obsolete

• 307 Temporary Redirect

the resource has temporarily moved and the original request method must be preserved

• 308 Permanent Redirect

the resource has permanently moved and the original request method must be preserved

## 4xx - Client Error Messages

• 400 Bad Request

the server cannot understand the request because it is malformed or invalid

• 401 Unauthorized

the request requires authentication and the client has not provided valid credentials

• 403 Forbidden

the server understands who the client is but refuses to allow access

• 404 Not Found

the server cannot find the requested resource

• 405 Method Not Allowed

the request method is valid but not allowed for this resource

• 409 Conflict

the request conflicts with the current state of the resource

• 410 Gone

the resource once existed but has been permanently removed

• 413 Content Too Large

the request body is larger than what the server is willing to process

• 415 Unsupported Media Type

the server does not support the format of the data sent in the request

• 418 I'm a teapot

the server refuses to perform the request as a joke response

• 422 Unprocessable Content

the request is syntactically valid but semantically incorrect

• 426 Upgrade Required

the server requires the client to switch to a different protocol

• 429 Too Many Requests

the client has sent too many requests in a short period of time

• 451 Unavailable For Legal Reasons

the resource cannot be served due to legal restrictions

## 5xx - Server Error Messages

• 500 Internal Server Error

the server failed in an unexpected way and does not know how to handle the request

• 501 Not Implemented

the server does not support the request method and cannot fulfill it

• 502 Bad Gateway

the server received an invalid response from an upstream server

• 503 Service Unavailable

the server is temporarily unable to handle the request due to overload or maintenance

• 504 Gateway Timeout

the server did not receive a response in time from an upstream server

• 507 Insufficient Storage

the server cannot complete the request because it has run out of storage

• 508 Loop Detected

the server detected an infinite loop while processing the request

• 511 Network Authentication Required

the client must authenticate to gain access to the network before the request can succeed

While I intended to avoid this blog becoming a dry reference table for obscure topics, the last blog and this one are quite literally just tables of information broken down into smaller sections of tables of information. Quality will pickup with time