HTTP status messages, also known as HTTP status codes, are a set of standardized responses that web servers provide to clients to indicate the outcome of a particular HTTP request. Each status code is a three-digit number that is included in the HTTP response header along with the response message.
There are five main categories of HTTP status codes:
- Informational (1xx): These codes indicate that the server has received the request and is processing it. They are used to provide feedback to the client during a long-running process.
- Successful (2xx): These codes indicate that the server has successfully processed the request and is returning the requested information. The most common status code in this category is 200 OK, which indicates that the request was successful.
- Redirection (3xx): These codes indicate that the client needs to take additional action to complete the request. For example, a 301 Moved Permanently code indicates that the requested resource has been permanently moved to a new URL.
- Client errors (4xx): These codes indicate that there was an error in the client’s request, such as requesting a non-existent resource or providing invalid parameters. The most common status code in this category is 404 Not Found.
- Server errors (5xx): These codes indicate that there was an error on the server side, such as a server outage or a misconfigured web application. The most common status code in this category is 500 Internal Server Error.
HTTP status codes are important for understanding the outcome of an HTTP request and for debugging issues in web applications and services. They are also used by web crawlers and other automated tools to navigate the web and collect information.