This week we're publishing several blog posts dedicated to helping you with one response code: 404.

Response codes are a numeric status (like 200 for "OK", 301 for "Moved Permanently") that a webserver returns in response to a request for a URL. The 404 response code should be returned for a file "Not Found".

When a user sends a request for your webpage, your webserver looks for the corresponding file for the URL. If a file exists, your webserver likely responds with a 200 response code along with a message (often the content of the page, such as the HTML).

200 response code flow chart


So what's a 404? Let's say that in the link to "Visit Google Apps" above, the link is broken because of a typing error when coding the page. Now when a user clicks "Visit Google Apps", the particular webpage/file isn't located by the webserver. The webserver should return a 404 response code, meaning "Not Found".

404 response code flow chart


Now that we're all on board with the basics of 404s, stay tuned 4 even more information on making 404s good 4 users and 4 search engines.