What server response codes do we consider "down" or indicate a problem?
What server response codes do we consider "up" / accessible?
We mark a website as up if it returns an HTTP status code anywhere within the 2xx or 3xx ranges. For example, most sites will respond with a 200 HTTP code, so we would mark that site as up. If the site returns a successful status code, but the content or body of the page is returning an error or otherwise not working correctly, we won't be able to detect tha and our site may show a false negative. In those cases you may want to contact the site owner to notify them of the problem.