SSL Certificate Checker Online Free
Instantly verify any domain's SSL certificate — validity, expiry date, issuer, subject alternative names, TLS protocol version, and SHA-256 fingerprint. No signup required.
How the SSL Certificate Checker Works
- 1Enter a domain name (e.g.
example.com) or include a port for non-standard HTTPS (e.g.example.com:8443). You can paste URLs directly — the protocol and path are stripped automatically. - 2Click Check SSL. Our server opens a TLS connection to the domain and reads the certificate presented during the handshake — the same certificate your browser validates when you visit the site.
- 3The status banner shows whether the certificate is valid, expiring soon (within 30 days), or expired. A validity timeline shows where today falls within the certificate's lifespan.
- 4Review the full details: subject and issuer fields, all Subject Alternative Names, the TLS protocol and cipher suite in use, the serial number, and the SHA-256 fingerprint — with copy buttons for each.
Why SSL Certificate Monitoring Matters
An expired certificate causes browsers to show a full-page security warning to every visitor, effectively taking your site offline. Let's Encrypt certificates expire after 90 days — short by design to encourage automation. Even longer-lived certificates from commercial CAs are now capped at 13 months by browser policy. Regular checks ensure you renew before expiry, and the 30-day warning window gives you time to act without scrambling.
The TLS protocol version matters too. TLS 1.0 and 1.1 are deprecated and blocked by modern browsers. Cipher suite selection affects both security and performance — TLS 1.3 with AEAD ciphers (AES-GCM, ChaCha20-Poly1305) is the current best practice.
SSL Certificate Tips
Automate renewal with Certbot
Let's Encrypt + Certbot runs a cron job that renews certificates automatically when fewer than 30 days remain. Set it up once and never manually renew again — but still monitor in case auto-renewal silently fails.
Check SANs match your domains
Browsers validate the domain against the SANs list, not the Common Name. If you added a new subdomain but forgot to include it in the certificate, visitors will get a name mismatch error even if the cert is otherwise valid.
Look for TLS 1.3
TLS 1.3 removes legacy cipher suites, is faster (1-RTT handshake vs 2-RTT for TLS 1.2), and offers forward secrecy by default. If your server still shows TLS 1.2 only, consider enabling 1.3 support.
Verify the issuer chain
The issuer field shows the certificate authority. If you see an unexpected or unknown CA, the certificate may have been replaced or misconfigured. Compare the SHA-256 fingerprint with what your browser shows in its padlock inspector.
Check non-standard ports too
APIs, mail servers (IMAPS 993, SMTPS 465), and admin panels often run on non-standard ports with their own certificates. Use the host:port format to check those independently of your main domain.
Set a calendar reminder
Even with auto-renewal, note the expiry date in a shared calendar. If the auto-renewal job breaks (permission change, DNS propagation issue, ACME challenge failure), a manual reminder is your safety net.
Frequently Asked Questions
What does an SSL certificate checker do?
It connects to the domain you enter on port 443 (or the port you specify) and reads the TLS certificate the server presents during the handshake. It then shows you the validity period, issuer, subject, subject alternative names (SANs), TLS protocol version, cipher suite, serial number, and SHA-256 fingerprint — all without you having to open browser DevTools or run openssl commands.
How do I check a non-standard port?
Include the port number in the domain field separated by a colon — for example example.com:8443 or mail.example.com:993. The tool connects to exactly that host and port. If you omit the port, it defaults to 443.
What does "Expiring Soon" mean?
Certificates with 30 days or fewer remaining are flagged as Expiring Soon with an amber warning. Most certificate authorities and monitoring tools use 30 days as the alert threshold because renewal typically takes a few days and you want buffer time before browsers start showing warnings.
What are Subject Alternative Names (SANs)?
SANs are the list of domain names a single certificate is valid for. Modern certificates use SANs instead of the older Common Name field to cover multiple domains — for example, one certificate might cover example.com, www.example.com, and api.example.com. Wildcard entries like *.example.com cover all subdomains at one level.
What TLS protocol versions should I see?
Modern servers should show TLS 1.3, which is the current standard and offers the best performance and security. TLS 1.2 is still widely supported and acceptable. TLS 1.1 and TLS 1.0 are deprecated and considered insecure — browsers have removed support for them. If you see an older version, the server configuration should be updated.
What is the SHA-256 fingerprint used for?
The fingerprint is a hash of the certificate's raw bytes. You can compare it with the fingerprint shown in a browser's certificate inspector to verify you are seeing the same certificate. It's also useful when pinning a specific certificate in a mobile app or internal service.
Does this tool send my domain to a third party?
No. The check is made by our own server directly to the domain you enter — it does not use any third-party certificate checking service. The domain name is sent to our server to initiate the check, but the raw certificate data is processed and returned immediately without being logged or stored.
Why might the check fail?
Common reasons: the domain does not exist (ENOTFOUND), port 443 is not open or is firewalled (ECONNREFUSED), the server takes more than 12 seconds to respond (timeout), or the server does not present any TLS certificate on that port. Internal or intranet domains that are not reachable from the internet cannot be checked.