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SSL Certificate Checker

Check any domain's SSL/TLS certificate — expiry, issuer, and Subject Alternative Names.

Unlike every other tool on this site, this one talks to a server — we connect to the domain you enter on port 443 to read its public certificate (browsers can't do this directly). See what we send →

Expiry at a Glance

See exactly when a certificate expires, with a clear warning badge once it's within 30 days — or already expired.

Issuer & Trust

See the certificate authority that issued the cert, and whether it's trusted by standard root stores — plus why, if it isn't.

Full SAN List

View every domain and wildcard covered by the certificate's Subject Alternative Names, not just the primary hostname.

How to Check an SSL Certificate

  1. Enter a domain name (e.g. example.com) into the input above — no need to include https://.
  2. Click “Check Certificate.” We connect to that domain on port 443 and read its public certificate.
  3. Review the result. Expiry date, issuer, trust status, and the full list of Subject Alternative Names are shown immediately.

Why This Tool Isn't Client-Side

Every other tool on Unformat.online runs entirely in your browser. This one is different: a browser's JavaScript has no API to read the TLS certificate metadata of a connection — that information is deliberately kept out of reach for security reasons. Actually inspecting a certificate's issuer, expiry, and SANs requires opening a real TLS connection to the target server, which only a server-side process can do. So this tool sends the domain name you enter to our server, which performs the handshake and sends back only the certificate metadata — never any of the connection's encrypted contents.

Frequently Asked Questions

Does this tool send my data to a server?

Yes — this is the one tool on Unformat.online that does. Only the domain name you type is sent; it is used solely to perform the certificate check and is never logged or stored. See our privacy policy for the full explanation.

Is it safe to enter a domain here?

Yes. Only enter public domain names — the tool connects the same way your browser would when visiting that site over HTTPS, and cannot reach private or internal network addresses.

What is a Subject Alternative Name (SAN)?

A SAN is an additional hostname a certificate is valid for, beyond its primary subject — for example a certificate for example.com often also lists www.example.com or a wildcard like *.example.com.

Why does my certificate show as expired or untrusted?

A certificate can be technically present but still show as untrusted: it may be self-signed, issued by a private CA, or have an incomplete chain. Expiry is calculated independently, so you'll see it even on a certificate that's otherwise untrusted.

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