X-Frame-Options X-Frame-Options tells the browser whether you want to allow your site to be framed or not. By preventing a browser from framing your site you can defend against attacks like clickjacking.

Strict-Transport-Security HTTP Strict Transport Security is an excellent feature to support on your site and strengthens your implementation of TLS by getting the User Agent to enforce the use of HTTPS.

X-Content-Type-Options X-Content-Type-Options stops a browser from trying to MIME-sniff the content type and forces it to stick with the declared content-type. The only valid value for this header is "X-Content-Type-Options: nosniff".

X-XSS-Protection X-XSS-Protection sets the configuration for the XSS Auditor built into older browsers. The recommended value was "X-XSS-Protection: 1; mode=block" but you should now look at Content Security Policy instead.

Content-Security-Policy Content Security Policy is an effective measure to protect your site from XSS attacks. By whitelisting sources of approved content, you can prevent the browser from loading malicious assets. Analyse this policy in more detail. You can sign up for a free account on Report URI to collect reports about problems on your site.

Referrer-Policy Referrer Policy is a new header that allows a site to control how much information the browser includes with navigations away from a document and should be set by all sites.

Feature-Policy Feature Policy has been renamed to Permissions Policy, see the details here.

Expect-CT Expect-CT allows a site to determine if they are ready for the upcoming Chrome requirements and/or enforce their CT policy.