Online Tool Store
HSTS Preload Checker
Enter a domain and check it against a small bundled sample of well-known preloaded domains to see how HSTS preload status is structured - for the authoritative, live answer use hstspreload.org.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Sample data only — not a live lookup. This checker compares your domain against a small bundled list of 18 well-known domains for illustration. It does not query the internet or the real HSTS preload list. For the authoritative, current status of any domain, check hstspreload.org.
Try one of the bundled sample domains, or any other domain to see a "not in sample" result.
Bundled sample domains
How it works
- Type a domain, or pick one of the bundled sample domains below the input.
- The domain is normalized and compared against the small dataset embedded in this page — no request ever leaves your browser.
- A match shows the sample's
includeSubDomainsflag; no match just means it is not one of the sample entries. - For the real, current answer for any domain, follow the link to hstspreload.org.
FAQ
Does this tool actually look up my domain online?
No, and this is worth being clear about: the checker never makes a network request. It compares whatever domain you type against a small bundled list of about eighteen well-known domains embedded directly in the page. It exists to show what a preload check looks like structurally, not to replace a real lookup.
Where should I check the real HSTS preload status of a domain?
At hstspreload.org, which is the official site backed by the Chromium project and is also the site you submit a domain to for preloading. Firefox and Safari ship the same underlying list, so a check there covers all major browsers, not just Chrome.
Why would my domain show as "not in this sample list" even though it really is preloaded?
Because the sample only contains a handful of illustrative domains, not the real list, which has well over one hundred thousand entries. A "not found" result here means only that the domain is not one of the eighteen bundled examples — it says nothing about its actual status. Always confirm with hstspreload.org.
What does "includeSubDomains" mean in the result?
It is one of the flags a site must send in its Strict-Transport-Security header to qualify for preloading — it means the HSTS policy applies to every subdomain, not just the exact host. The real preload list requires it, along with a long max-age and a preload directive, before Chromium will accept a submission.
What is HSTS preloading, briefly?
Normally a browser only enforces HTTPS-only access to a site after it has seen that site send an HSTS header once, which leaves the very first visit vulnerable to a downgrade attack. Preloading solves that by baking a fixed list of domains directly into the browser, so HTTPS is enforced even on a domain's first-ever visit.
How we compare
| Feature | This sample checker | hstspreload.org |
|---|---|---|
| Makes a live network lookup | No | Yes |
| Coverage | ~18 illustrative domains | The full, current list |
| Can submit a domain for preloading | No | Yes |
| Runs entirely in the browser, no accounts | Yes | Yes |
This tool is a quick, offline demonstration of what an HSTS preload check looks like. It is deliberately not a substitute for hstspreload.org, which holds the real list and is the only place that can tell you a domain's actual, current status.