Minify your HTML by removing all the unnecessary characters.
Minify your JS by removing all the unnecessary characters.
Get approximate IP details.
Find A, AAAA, CNAME, MX, NS, TXT, SOA DNS records of a host.
Get all possible details about an SSL certificate.
Make sure your passwords are good enough.
Get & verify the meta tags of any website.
Get the web-host of a given website.