Mobile-First Indexing: What It Means for You
Google indexes the mobile version of your site. If mobile is weaker than desktop, rankings suffer.
Read article →How it works
- Enter a domain name (for example
example.com) that serves HTTPS. - The tool opens a live TLS connection to the host on port 443.
- It reads the certificate the server presents during the handshake.
- You get the issuer, dates, days remaining and SAN list, all from the live certificate.
What it shows
- Issuer — the certificate authority that signed the certificate.
- Subject — the primary common name the certificate is issued for.
- Valid from — the date the certificate became active.
- Valid to — the expiry date after which browsers will warn.
- Days remaining — how long until the certificate expires.
- SAN domains — every host name the certificate is valid for.
- Validity status — whether the certificate is currently active or expired.
- Serial number — the unique identifier assigned by the issuer.
Common use cases
- Preventing outages — spot a certificate that expires soon before browsers block the site.
- Verifying coverage — confirm a certificate's SAN list includes
wwwand all subdomains. - After a migration — check the new host serves a valid certificate for the domain.
- Security review — confirm a trusted issuer signed the certificate in use.
Example
Check example.com and you might see a certificate issued by Let's Encrypt, valid for 90 days with 47 days remaining, covering both example.com and www.example.com in its SAN list — clear confirmation HTTPS is healthy and the renewal is not yet urgent.
Frequently asked questions
Is the SSL Certificate Checker free?
Yes — completely free, with no signup and no usage limits. Check as many domains as you need.
Does HTTPS affect SEO?
Yes. HTTPS is a confirmed Google ranking signal, and an expired or mismatched certificate triggers browser warnings that drive visitors away. Keeping a valid certificate is part of basic technical health.
What should I do if the certificate is about to expire?
Renew or reissue it through your host or certificate authority, then recheck here to confirm the new dates. To plan a clean move to HTTPS, read our HTTPS migration guide and verify the redirect setup with the Redirect & HTTP Status Checker and HTTP Header Checker tools.