If you run a website, we have all been there, you go to load up your site and you get nothing but an error message. But what do these mean?

Every error page you see on a website should have a 3 digit status code displayed. The first digit marks the class of the status code. The first three do not result in an error page, your browser understands what to do and deals with it without interrupting your experience:

  • 1XX status codes have informational purposes
  • 2XX indicates success
  • 3XX is for redirection

When we do see an error page it is usually down to the 4XX and 5XX kind:

  • 4XX represent client-side errors
  • 5XXs indicate problems on the server side

In these cases your browser doesn’t know what to do and shows an error.

Client-Side Errors (4XX)

400 – Bad Request

When your browser sends a request to the server, which the server is unable to understand, this error is shown. The reason is most likely that there’s something unstable on your side of the connection: for example, an unstable internet connection, a defective browser or a caching problem.

401 – Authorization Required

When you request a password-protected web page, the server responds with a 401 Authorization Required code. Your browser will normally show a popup that asks the user to provide a login-password combination. If you provide these, everything is all right, otherwise you are shown this error.

403 – Forbidden

You see this error when the server understands your request clearly, but for some reasons refuses to fulfil it. The most common reason is that the website owner doesn’t permit visitors to browse the file directory structure of the site or the specific file your requested doesn’t have the permission to be viewed from the web.

404 – Not Found

404 is the most well-known code out there. The browser returns a 404 HTML page when the server doesn’t find anything on the requested location. Either you mistyped the URL, or the permalink structure of the site has been changed and the incoming URL point to page that were renamed or moved to a different location.

408 – Request Time-Out

When your request takes too long, the server times out, closes the connection, and the browser displays a 408 Request Time-Out error message. The time-out happens because the server didn’t receive a complete request from the client within the timeframe it was prepared to wait. Persistent 408 errors can occur because of the heavy workload on either the server or on the client’s system.

410 – Gone

The 410 Gone error page is very close to the well-known 404. Both mean that the server doesn’t find the requested file, but while 404 suggests that the target file may be available somewhere on the server, 410 indicates a permanent condition.

Server Errors (5XX)

500 – Internal Server Error

Internal Server Error is the most well-known server error, as it’s used whenever the server encounters an unexpected condition that prevents it from fulfilling your request.

502 – Bad Gateway

This error represents a communication problem between two servers. It occurs when you connect to a server acting as a gateway or a proxy that then talks to another server. When you encounter the Bad Gateway error page the first server receives an invalid response from the second server.

503 – Service Temporarily Unavailable

You see this error any time there’s a temporary overload on the server, or when it’s going through a scheduled maintenance. The 503 error code means that the web server is currently not available. This is usually a temporary condition that will be resolved after some delay.

504 – Gateway Time-Out

There is another server-server communication problem. This error is should when the first server doesn’t receive a timely response from the second server it connected with.