Last updated: 2026-07-19
What Is an SSL Certificate?
Definition
An SSL (Secure Sockets Layer) certificate is a digital certificate that authenticates a website's identity and enables an encrypted connection. Modern certificates use TLS (Transport Layer Security) but are still commonly called SSL certificates. When a browser connects to a site with a valid SSL certificate, you see the padlock icon and "https://" in the address bar.
Why it matters
SSL certificates expire. When a certificate expires, browsers block access to your site with a security warning that scares users away. Certificate expiration is one of the most common causes of preventable downtime. Let's Encrypt has made certificates free and automated renewal common, but automated renewals can fail: DNS changes, firewall rules, or misconfigured web servers can all break certificate renewal.
Example
A company moved their website to a new server and forgot to update the Let's Encrypt renewal cron job. 90 days later, the certificate expired. Visitors saw a "Your connection is not private" warning. It took an hour to manually renew the certificate, during which time new user signups dropped to zero. PingWatchdog SSL monitoring would have alerted them 30 days before expiration.
How PingWatchdog helps
PingWatchdog monitors your SSL certificates and alerts you 30, 14, and 7 days before expiration. You also get alerts for certificate chain issues, mismatched domains, and expired intermediate certificates. SSL monitoring is included on every PingWatchdog plan at no extra cost.