Certificate Fields Explained
Subject / CNThe domain name the certificate is issued for (Common Name)
IssuerThe Certificate Authority that issued and signed the certificate (e.g. Let's Encrypt, DigiCert)
Valid FromDate the certificate became valid (Not Before)
Valid UntilExpiry date — browser warnings appear after this date (Not After)
SANsSubject Alternative Names — all domains covered by this certificate
Certificate ChainIntermediate CA certificates linking the domain cert to a trusted root CA
How to Use It
1
Open the tool
Go to Network & Security and scroll to the SSL Certificate Checker.
2
Enter a domain
Type the domain name (e.g. example.com). Port 443 is used by default.
3
View certificate details
See the issuer, validity period, expiry date, SANs (all covered domains) and chain.
4
Check expiry
Note the expiry date. Set up monitoring to alert you 30 days before expiry to avoid outages.
Pro Tips
💡Let's Encrypt certificates expire every 90 days — use Certbot with auto-renewal or a managed hosting platform to renew automatically.
💡An expired certificate causes a hard browser error — all visitors see a "not secure" warning and most will leave. Monitor expiry 30+ days in advance.
💡Check that all your subdomains are covered in the SANs. Wildcard certificates (
*.example.com) cover one level of subdomain but not sub.sub.example.com.Frequently Asked Questions
What is an SSL/TLS certificate?
Authenticates a website's identity and enables encrypted HTTPS connections. Contains domain name, issuing CA, validity period and public key used for the TLS handshake.
How do I know if it's expiring?
Check the "Not After" / "Valid Until" field. Set monitoring alerts 30 days before expiry. Let's Encrypt certs expire every 90 days.
What are SANs?
Subject Alternative Names — list all domains covered by the certificate. One cert can cover example.com, www.example.com, api.example.com. Modern browsers require SANs.
DV vs OV vs EV?
DV (Domain Validated) — verifies domain control only, fastest. OV (Org Validated) — verifies company. EV (Extended Validation) — strictest vetting. All provide the same encryption strength.
Check an SSL certificate now
Open the SSL Certificate Checker and verify any domain's certificate details — free, instant, no login.
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