Header Peek by Scrap Labs

Header Peek answers a simple question about any page you are on: which of the headers that matter did the server bother to send? Right-click the page or any link and choose Peek at the response headers. The add-on fetches the URL fresh, reads the response, and pops a notification listing six headers that harden a site: Strict-Transport-Security, Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, Referrer-Policy and Permissions-Policy. Each shows the first value it sent; the ones that never arrived are called out as missing, so a missing header is a finding, not a mystery. Results are kept only for the last check on the device. Built by Scrap Labs, the team behind Hackedself, a publication about biohacking protocols, supplement evidence and the security hygiene of the tools a self-experimenter runs.