HSTS Checker Tool — Free Online Test
Free HSTS checker online and strict transport security checker — test max-age, includeSubDomains, and HSTS preload check on any HTTPS URL. Instant results, no signup.
- Strict-Transport-Security header presence
- max-age and includeSubDomains
- HSTS preload check
What This Tool Checks
- Strict-Transport-Security header presence
- max-age and includeSubDomains
- HSTS preload check
Why It Matters
HSTS is one of the clearest transport-hardening controls, but it only helps when the policy is strong, consistent, and aligned with preload or subdomain expectations. This HSTS checker tool runs a free online test of max-age, includeSubDomains, and preload eligibility.
Best For
Best for teams validating HTTPS enforcement after certificate changes, CDN updates, subdomain expansion, or a broader transport-security hardening pass.
What To Do Next
Use the result to confirm whether you only need a policy adjustment or whether you should review redirect behavior, subdomain readiness, and preload eligibility too.
Related Resources
Frequently Asked Questions
An HSTS checker tool is a free online test of the Strict-Transport-Security response header. Vulnify reads max-age, includeSubDomains, and preload eligibility so you can confirm HTTPS is enforced before browsers will trust the policy.