Security Headers Checker
Grade HTTP security headers against best practices. Check HSTS, CSP, X-Frame-Options and more.
Frequently Asked Questions
What are HTTP security headers?
HTTP security headers are response headers sent by a web server that instruct browsers on how to behave when handling a site's content. They provide an additional layer of security by preventing common web attacks. The most important headers include Content-Security-Policy (CSP), Strict-Transport-Security (HSTS), X-Frame-Options, X-Content-Type-Options, Referrer-Policy, and Permissions-Policy. Security headers are free to implement and have significant impact on your site's security posture.
Which security header is most important to implement first?
X-Content-Type-Options: nosniff is the easiest and lowest-risk header to add — it prevents MIME-type sniffing attacks with no configuration required. Next, add Strict-Transport-Security (HSTS) to enforce HTTPS, and X-Frame-Options: DENY to prevent clickjacking. Content-Security-Policy provides the strongest protection but requires the most configuration effort. Start with the simpler headers to get quick wins, then work toward a full CSP.
What does an A or F grade mean for security headers?
A security header grade reflects how many recommended headers are present and correctly configured. An A or A+ grade means most or all recommended headers are set with strong values. An F grade means several critical headers are missing. The grade is a useful starting benchmark — however, a header with a weak value (e.g. X-Frame-Options: ALLOWALL) may score points while providing little real protection. Review each header's configuration, not just the overall grade.
Do security headers affect SEO?
Security headers do not directly affect search engine rankings. However, HTTPS enforcement via HSTS is important since Google uses HTTPS as a ranking signal. Additionally, misconfigured headers (such as an overly strict CSP that blocks CSS or JavaScript) can break page rendering, which would indirectly harm user experience signals. Implementing security headers correctly improves your security posture without negatively affecting SEO.