Error codes generally come in the form of 4xx and 5xx statuses. Error codes at the 400 level mean there was a client-side error — think of something like the user typing the wrong URL in the address bar. Error codes at the 500 level mean there was a server-side error — think of something like the database server going down or perhaps running out of disk space.
Two of the most popular error codes are 403 and 404, and you can set custom pages or use our default error message for them.
404 Not Found
The most common error code you run into is a 404 error. The 404 status code means the requested resource is no longer available or, more specifically, just not found.
What are some of the reasons for a 404 error? Typos are a common reason for getting a 404 error. A missing or extra letter in a typed-in url, or a wrong domain name can often result in a 404 error. Another reason for 404 errors isn’t typos; it is the aging of the web. When someone writes an article or blog, that person might link to a secondary source to provide additional information for the article. Now imagine revisiting said article six months or six years later. If what was linked to is no longer on the web, a 404 error will be generated when you click on the link in the browser. For this reason, one should only change one's page names when absolutely necessary.
Another common client-side response status code is 403. Getting a 403 status code back from an HTTP request means access to the resource is forbidden. This is not an authentication problem; those are 401 (unauthorized) errors. Error code 403 indicates that the user does not have the properly permissions to access the file or directory.