SSL Certificate Checker

Check a domain's SSL certificate & expiry.

Check any website's SSL/TLS certificate in seconds. Opens a real TLS handshake to the domain and reports whether the certificate is valid and trusted, how many days until it expires, who issued it, the domains it covers (SANs), the key size and SHA-256 fingerprint, and the negotiated TLS protocol and cipher — plus the full certificate chain. Warns on expired, self-signed and hostname-mismatch certificates. Free, no sign-up, no API key.

SSL Certificate Checker features

How to use SSL Certificate Checker

  1. Enter your domain

    Type any hostname like example.com into the box — no https prefix needed — to check its live SSL/TLS certificate.

  2. Run the check

    Click Check SSL and the tool opens a TLS handshake to port 443, reads the certificate the server presents and inspects the whole chain.

  3. Read the verdict

    See at a glance whether the certificate is valid and trusted, expiring soon, expired, self-signed or issued for the wrong hostname.

  4. Review the details

    Check the issuer, validity dates, days remaining, subject alternative names, key size, serial number and SHA-256 fingerprint.

  5. Inspect the chain & connection

    Confirm the chain builds up to a trusted root and review the negotiated TLS protocol and cipher for weak or outdated settings.

Frequently asked questions

What does the SSL Certificate Checker do?

It opens a real TLS handshake to your domain on port 443 and reads the exact certificate the server presents — then reports whether it's valid and trusted, when it expires, who issued it, which domains it covers, the key details and the negotiated TLS protocol and cipher.

Why does it say my certificate is 'not trusted' or self-signed?

The chain the server sent doesn't build up to a certificate authority in the standard trust store. That usually means the certificate is self-signed, or the server is missing an intermediate certificate. Browsers will show a warning until the full chain is served.

What's a hostname mismatch?

The certificate is otherwise valid, but the domain you checked isn't listed in its Common Name or Subject Alternative Names. Browsers will reject it for that host — you need a certificate issued for this exact domain (or a matching wildcard).

How early should I renew before expiry?

Renew at least a couple of weeks before the expiry date. This tool flags a certificate as 'expiring soon' when 14 or fewer days remain, so you have time to reissue and deploy before visitors see an error.

Is it free and does it need an API key?

It's completely free with no signup and no API key. The check runs on our server using a standard TLS handshake and a light anti-abuse rate limit is the only cap. Nothing about your certificate is stored.

Can it check certificates on a port other than 443?

The public tool checks the standard HTTPS port 443. For internal hosts or non-standard ports, a private or loopback address is intentionally blocked for security — the checker only inspects publicly reachable hosts.

How do I check when my SSL certificate expires?

Enter your domain and the checker opens a live TLS handshake and reports the exact expiry date and the number of days remaining, flagging it as 'expiring soon' when 14 or fewer days are left — so you can renew before visitors hit a security warning.

Why is my site showing 'Not Secure' or a certificate error?

Common causes are an expired certificate, a hostname that isn't listed in the certificate (mismatch), a self-signed certificate, or a missing intermediate in the chain. Run the check here — it identifies which of these applies so you know exactly what to fix.

Related tools — Site diagnostics