Minify your HTML by removing all the unnecessary characters.
Minify your JS by removing all the unnecessary characters.
Make sure your passwords are good enough.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Check if the URL is banned and marked as safe/unsafe by Google.
Get the web-host of a given website.
Get & verify the meta tags of any website.
Parse details from user agent strings.