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Bulk up to 100 • Issuer + dates • Expiring soon detection

SSL Certificate Checker

Paste domains or URLs — we’ll connect via TLS to :443, read the certificate, and show issuer, CN/SAN, validity, and days left.

Paste up to 100 domains/URLs (one per line)
Tip: Hostname mismatch often means the cert is for a different domain (or missing SAN entry).

Results

Host Certificate HTTP Hops Time Issues
Run a check to see results here.
“Expiring soon” is based on your selected threshold.

Quick interpretation

SSL/TLS certificate issues can break HTTPS or show browser warnings.

  • OK valid certificate with hostname match
  • Warning expiring soon, mismatch, not yet valid
  • Error expired or TLS handshake failure
HTTPS trust

SSL Certificate Checker: verify issuer, validity, and hostname match

This tool checks the TLS certificate presented on port 443 and highlights common problems: expired certs, certificates that don’t match the domain, and certificates that are about to expire. Use it to prevent browser warnings and unexpected HTTPS downtime.

Common problems

  • Expired certificates cause hard browser warnings and failed secure requests.
  • Hostname mismatch happens when the cert CN/SAN doesn’t include your domain.
  • Expiring soon means you should renew before automated clients start failing.

FAQ

Why does the checker use port 443 even if I enter an HTTP URL?

SSL/TLS certificates are negotiated over HTTPS on port 443. Even if you paste an http:// URL, the tool connects to port 443 to read the certificate that would be used for secure connections.

What does “hostname mismatch” mean?

Hostname mismatch means the tested domain is not listed in the certificate’s identity. Modern clients validate hostnames against the SAN list first and fall back to CN only if SAN is missing.

If the domain is not present as an exact name or valid wildcard, browsers will show HTTPS warnings.

What is the difference between CN and SAN?

CN (Common Name) is the legacy primary domain field. SAN (Subject Alternative Name) lists all valid hostnames for the certificate.

Today, SAN is authoritative. If SAN exists, CN is ignored during hostname validation.

Why can a wildcard certificate still fail validation?

Wildcards only match one subdomain level. For example, *.example.com matches www.example.com but not example.com or a.b.example.com.

Mismatch also occurs if the server presents a default certificate due to incorrect SNI configuration.

What does “expired” SSL certificate mean?

An expired certificate has passed its Valid to date. Browsers show hard security warnings and many HTTPS clients refuse the connection.

This can break logins, APIs, feeds, and cause traffic loss.

What does “expiring soon” indicate?

“Expiring soon” means the certificate will expire within the selected threshold (for example, ≤ 30 days).

The certificate is still valid, but renewal should be done early to avoid outages if automation fails.

What does “not yet valid” mean?

This status appears when the certificate’s Valid from date is in the future.

Clients treat such certificates as invalid until the start date is reached.

What causes a TLS handshake error?

A TLS handshake error means the secure connection could not be established.

Common reasons include no HTTPS service on port 443, blocked port, broken TLS configuration, or the server not presenting a certificate.

Does this tool fully validate the certificate trust chain?

No. The checker reads the presented certificate and reports basic chain count, issuer, and validity.

It does not replicate full browser trust store validation, which depends on local CA stores.