HTTP status codes are like short notes from a server that get tacked onto a web page. They’re not actually part of the site’s content. Instead, they’re messages from the server letting you know how things went when it received the request to view a certain page.
These kinds of messages are returned every time your browser interacts with a server, even if you don’t see them. If you’re a website owner or developer, understanding HTTP status codes is critical. When they do show up, HTTP status codes are an invaluable tool for diagnosing and fixing website configuration errors.
This article introduces several server status and error codes, and explains what they reveal about what’s happening on the server behind the scenes.
Let’s dive in!
What Are HTTP Status Codes?
Every time you click on a link or type in a URL and press Enter, your browser sends a request to the webserver for the site you’re trying to access. The server receives and processes the request, and then sends back the relevant resources along with an HTTP header.
HTTP status codes are delivered to your browser in the HTTP header. While status codes are returned every single time your browser requests a web page or resource, most of the time you don’t see them.
It’s usually only when something goes wrong that you might see one displayed in your browser. This is the server’s way of saying: “Something isn’t right. Here’s a code that explains what went wrong.”
If you want to see the status codes that your browser doesn’t normally show you, there are many different tools that make it easy. Browser extensions are available for developer-friendly platforms such as Chrome and Firefox, and there are many web-based header fetching tools like Web Sniffer.
To see HTTP status codes with one of these tools, look for the line appearing near the top of the report that says “Status: HTTP/1.1”. This will be followed by the status code that was returned by the server.
Understanding HTTP Status Code Classes
HTTP status codes are divided into 5 “classes”. These are groupings of responses that have similar or related meanings. Knowing what they are can help you quickly determine the general substance of a status code before you go about looking up its specific meaning.
The five classes include:
- 100s: Informational codes indicating that the request initiated by the browser is continuing.
- 200s: Success codes returned when browser request was received, understood, and processed by the server.
- 300s: Redirection codes returned when a new resource has been substituted for the requested resource.
- 400s: Client error codes indicating that there was a problem with the request.
- 500s: Server error codes indicating that the request was accepted,
This article was written by Jon Penland and originally published on Blog – Kinsta Managed WordPress Hosting.