SSL Certificate Checker
Inspect any HTTPS site's SSL/TLS certificate — issuer, subject, validity window, days to expiry, alternative names and the full chain.
What is an SSL certificate checker?
An SSL (really TLS) certificate proves a website's identity and encrypts traffic to it. Certificates expire — often every 90 days — and an expired or misconfigured certificate throws a scary browser warning that drives visitors away. This checker performs a live TLS handshake with the host, reads the certificate it presents, and shows you exactly when it expires and whether the chain is trusted, so you can renew before anything breaks.
What to watch for
- Days to expiry — renew well before it hits zero; aim for 30 days of buffer.
- Subject alternative names — the exact hostnames the cert is valid for.
- Issuer — the certificate authority that signed it.
- Chain — a missing intermediate is the most common “works in browser, fails in API” bug.
How to use it
- 1Enter a hostname such as example.com.
- 2Click Check SSL to open a TLS connection on port 443.
- 3Review the expiry countdown and validity badge at the top.
- 4Expand the SAN list and chain to confirm coverage and trust.
Frequently asked questions
What does this SSL checker tell me?+
It connects to the host on port 443 and reports the certificate's subject and issuer, the valid-from and valid-to dates, exact days until expiry, the negotiated TLS protocol, the Subject Alternative Names it covers, and the issuing chain up to the root.
How do I fix a certificate that's about to expire?+
Renew and reinstall it before the valid-to date. If you use Let's Encrypt, ensure your ACME client (like Certbot or Caddy) is renewing automatically — most certs are 90 days and should renew around 30 days out.
Why does it say the certificate is valid but the name doesn't match?+
A certificate can be cryptographically valid yet issued for a different hostname. Browsers reject that as a name mismatch. Check the Subject Alternative Names list — the hostname you're visiting must appear there.
Can it check expired or self-signed certificates?+
Yes. It inspects and reports on the certificate even when validation fails, so you can diagnose expired, self-signed, or misconfigured chains rather than just seeing an error.