HTTP Status Codes: According To RFC 9110

Decoding HTTP Status Code

In the world of web communication, HTTP status codes serve as critical indicators of the success, redirection, client errors, and server errors encountered during the exchange of data between clients and servers. These codes, grouped into different series, provide valuable insights into the outcome of each request, aiding in the effective management and troubleshooting of web transactions. Understanding the implications of these status codes is vital for web developers, administrators, and anyone involved in maintaining an efficient and user-friendly online experience. In this comprehensive guide, we delve into the intricate details of various HTTP status codes, offering a deeper understanding of their significance and practical application in web communication.

1xx Informational Responses:

1. 100 Continue:
   • Explanation: This status code indicates that the initial part of the request has been received by the server, and the client should proceed to send the remainder of the request.
   • Use Case: It is commonly used in scenarios where the server needs to inform the client to continue sending the request, especially for large or complex requests that require multiple steps for processing.
2. 101 Switching Protocols:
   • Explanation: The server acknowledges that it understands and is willing to comply with the client’s request for a change in the protocol used on the connection.
   • Use Case: It is frequently employed during the process of upgrading or switching between different protocols, allowing both the client and server to agree on a mutually acceptable protocol for communication.
3. 102 Processing:
   • Explanation: This status code implies that the server has received the request and is currently processing it, but no response is available at that moment.
   • Use Case: It is often used when the server needs more time to assemble the response, especially in cases where the processing of the request involves complex operations that require a significant amount of time.
4. 103 Early Hints:
   • Explanation: Primarily used with the Link header, this status code enables the server to send hints to the user agent to start preloading resources while the server is still preparing the final response.
   • Use Case: It is employed to optimize performance by allowing the user agent to proactively initiate the loading of additional resources that are likely to be required based on the initial request, thereby reducing latency and improving page load times.

2xx Success Responses:

1. 200 OK:
   • Explanation: This status code indicates that the request has succeeded, and the server has returned the requested resource.
   • Use Case: It is one of the most common status codes, confirming that the client’s request was successful, and the server has provided the expected data.
2. 201 Created:
   • Explanation: The server has successfully fulfilled the request and created a new resource.
   • Use Case: It is often utilized after successful POST requests to indicate that a new resource has been created as a result of the request.
3. 202 Accepted:
   • Explanation: This code suggests that the request has been accepted for processing, but the processing has not been completed.
   • Use Case: It is typically used when the server needs more time to complete the requested operation, and the final outcome of the request is still pending.
4. 203 Non-Authoritative Information:
   • Explanation: The server is a proxy, and the response is a representation of the resource requested, but it is from a third-party copy, not the original server.
   • Use Case: It is used when the server provides a cached or mirror copy of the requested resource, indicating that the returned information might not be exactly the same as the original source.

3xx Redirection Responses:

1. 300 Multiple Choices:
   • Explanation: The requested resource has multiple choices available, and the user or user agent must select one from them.
   • Use Case: It is typically used when there are multiple options available for the resource requested, and the server cannot determine the most suitable choice automatically.
2. 301 Moved Permanently:
   • Explanation: The requested resource has been permanently moved to a new location, and the new URI is provided in the response.
   • Use Case: It is commonly used when a resource has been relocated permanently, and the client should update its records with the new URI provided by the server.
3. 302 Found:
   • Explanation: The requested resource is temporarily located at a different URI, but further changes might occur in the future.
   • Use Case: It is often used to indicate that the resource is temporarily available at a different location, and the client should use the provided URI for future requests.
4. 303 See Other:
   • Explanation: The server is instructing the client to retrieve the requested resource from a different URI using a GET request.
   • Use Case: It is commonly used in redirection scenarios where the server wants the client to access the resource from a different URI using the GET method.

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4xx Client Error Responses:

1. 400 Bad Request:
   • Explanation: The server cannot process the request due to a client error, such as malformed syntax or invalid request framing.
   • Use Case: It is frequently used when the server encounters issues with the client’s request that prevent it from being processed correctly.
2. 401 Unauthorized:
   • Explanation: This status indicates that the request requires user authentication, and the client needs to provide valid credentials for access.
   • Use Case: It is commonly used when the server requires the client to authenticate itself before granting access to the requested resource.
3. 402 Payment Required:
   • Explanation: This status code is reserved for future use, possibly for digital payment systems, although it is not widely used in practice.
   • Use Case: While it is not commonly encountered, it is intended for scenarios where payment is required before accessing the requested resource.
4. 403 Forbidden:
   • Explanation: The server understood the request, but the client is not authorized to access the requested resource.
   • Use Case: It is often used to restrict access to certain resources, indicating that the client’s identity is known, but access is still prohibited.

5xx Server Error Responses:

1. 500 Internal Server Error:
   • Explanation: The server encountered an unexpected condition that prevented it from fulfilling the request.
   • Use Case: It is commonly used when the server faces an internal error that hinders its ability to process the request and provide the expected response.
2. 501 Not Implemented:
   • Explanation: The server does not support the functionality required to fulfill the request.
   • Use Case: It is typically used when the server lacks the necessary functionality or resources to handle the specific request made by the client.
3. 502 Bad Gateway:
   • Explanation: This error response indicates that the server, acting as a gateway or proxy, received an invalid response from an upstream server.
   • Use Case: It is often used when the server, acting as an intermediary, encounters issues while trying to process the request through an upstream server.
4. 503 Service Unavailable:
   • Explanation: The server is temporarily unable to handle the request due to maintenance, overloading, or other temporary conditions.
   • Use Case: It is frequently used when the server is undergoing maintenance or experiencing high traffic, making it temporarily unavailable to handle incoming requests.

Here you can find more info World Wide Web Consortium (W3C) – HTTP Protocol