Free Tool

SSL Certificate Checker

Enter any domain to inspect its SSL certificate. See the issuer, expiry date, days remaining, certificate chain, protocol, and cipher strength - instantly.

What this tool checks

This free SSL checker connects to your domain over TLS, extracts the certificate, and inspects it for common issues. Here's what it reports:

Expiry date & days remaining

Certificate issuer (CA)

Certificate chain validity

Subject & SANs (covered domains)

TLS protocol version

Cipher suite & strength

SHA-256 fingerprint

Serial number

Why SSL certificates expire

SSL/TLS certificates have a maximum validity period - currently 397 days for publicly trusted certificates. When a certificate expires, browsers show a security warning and most users leave immediately. Auto-renewal services like Let's Encrypt reduce this risk, but they fail silently more often than expected - expired payment methods, DNS validation failures, and misconfigured renewal hooks all cause certificates to lapse without warning.

Manual checks vs. continuous monitoring

This tool gives you a point-in-time snapshot of your certificate's health. For production services, you need continuous monitoring that checks automatically and alerts your team days or weeks before expiry. Vantaj monitors your SSL certificates 24/7 and sends alerts at 90, 60, 30, 7, and 1 day before expiry - so renewals never slip through the cracks.

Frequently asked questions

How does this SSL checker work?

It connects to your domain over TLS (port 443 by default), performs a full handshake, and extracts the certificate details from the server's response - the same way a web browser does. No agents or access to your server required.

Can I check certificates on non-standard ports?

Yes. Enter your domain with a port number (e.g., api.example.com:8443) and the tool will check the certificate served on that port.

What does "chain invalid" mean?

A certificate chain connects your server's certificate to a trusted root CA through intermediate certificates. If an intermediate is missing or expired, browsers will show a security warning even if the leaf certificate is valid. This is one of the most common SSL issues.

How often should I check my SSL certificates?

For a manual spot-check, once a month is reasonable. For production services, use automated monitoring that checks daily and alerts you well before expiry. Vantaj starts alerting 90 days before expiry.

Is this tool free?

Yes, completely free with no signup required. For continuous automated monitoring with alerts, check out Vantaj's free tier which includes SSL monitoring for up to 20 domains.