SSL Certificate Checker Online — Verify HTTPS and Diagnose TLS Issues

What Is an SSL Certificate?

An SSL/TLS certificate is a digital certificate that authenticates a website's identity and enables encrypted HTTPS connections. Issued by trusted Certificate Authorities (CAs) like Let's Encrypt, DigiCert, and Sectigo, certificates contain the domain name, issuer, validity period, and public key. Every website that handles user data should use HTTPS with a valid certificate.

In 2026, free certificates from Let's Encrypt are standard — there's no reason not to have HTTPS. But certificates still expire (typically every 90 days for Let's Encrypt), misconfiguration is common, and certificate chain issues can cause silent failures that are hard to debug without the right tools.

How to Use an SSL Certificate Checker Online

1. Enter the domain name — e.g. example.com or api.example.com
2. Click Check — the tool connects to the server and retrieves certificate information.
3. Review the expiry date — ensure the certificate doesn't expire soon.
4. Check the certificate chain — all intermediate certificates must be properly installed.
5. Verify the domain match — the certificate must cover the exact domain (or wildcard).
6. Review TLS version — TLS 1.2 minimum; TLS 1.3 preferred in 2026.

Key Information an SSL Checker Reveals

• Expiry date — when the certificate expires; set up alerts 30 days before.
• Issuer (CA) — Let's Encrypt, DigiCert, Sectigo, or others.
• Certificate type — DV (Domain Validation), OV (Organization Validation), or EV (Extended Validation).
• SANs (Subject Alternative Names) — all domains the certificate is valid for.
• Chain completeness — whether intermediate certificates are correctly installed.
• TLS version and cipher suites — security rating of the server's TLS configuration.

Use Cases

Preventing Certificate Expiry Outages

A forgotten certificate expiry is a common cause of production outages. HTTPS stops working, browsers show scary warning pages, and customers can't access the site. Checking certificates regularly and setting automated renewal with certbot or your cloud provider prevents this entirely.

Diagnosing Mixed Content and HTTPS Errors

When browsers show "Not Secure" or HTTPS padlock errors, an SSL checker quickly reveals whether the certificate itself is invalid, expired, mismatched, or has a broken chain — pointing you directly to the fix needed.

Frequently Asked Questions

How often do SSL certificates expire?

Let's Encrypt certificates expire every 90 days. Commercial certificates (DigiCert, Sectigo) typically last 1 year. Browser trust policies are moving toward shorter maximum lifetimes — Apple has proposed 47-day maximum validity, which would require automated renewal for all certificates.

What is a certificate chain and why does it matter?

SSL certificates are issued in a chain: root CA → intermediate CA → end-entity (your domain) certificate. The server must send the intermediate certificates along with your domain certificate. If intermediates are missing, some clients (especially older systems) can't verify the certificate and show an error.

What is the difference between DV, OV, and EV certificates?

DV (Domain Validation) only verifies domain ownership — issued instantly, free via Let's Encrypt. OV (Organization Validation) verifies the organization's legal identity. EV (Extended Validation) has the strictest vetting and historically showed the green address bar (now removed in most browsers). For most sites, DV is sufficient.

How do I check an SSL certificate from the command line?

Use OpenSSL: openssl s_client -connect example.com:443 -showcerts to show the full chain, or echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates to show just the expiry dates.

What should I do when an SSL certificate is about to expire?

For Let's Encrypt, run certbot renew or check that your auto-renewal cron job is functioning. For commercial certs, purchase a renewal and install the new certificate before expiry. Cloudflare, AWS ACM, and most cloud platforms handle renewal automatically.