I built securityheaders.io after deploying security headers like CSP and HSTS to my own site. I wanted a quick and easy way to check if other sites were using these headers and I figured I'd turn it into a useful tool for everyone to use!
There are services out there that will analyse the HTTP response headers of other sites but I also wanted to add a rating system to the results. The HTTP response headers that this site analayses provide huge levels of protection and it's important that sites deploy them. Hopefully, by providing an easy mechanism to assess them, and further information on how to deploy missing headers, we can drive up the usage of security based headers across the web.