Verify SSL certificate
Your server might be serving your webpages, but is your SSL certificate still valid? OnlineOrNot can alert you when it detects an invalid SSL certificate on your page.
When creating a new uptime check, or editing an existing one, you can enable SSL verification by ticking the "Verify SSL certificate" checkbox under Advanced settings, as shown below:
When OnlineOrNot detects an invalid SSL certificate, your uptime check will go into a "DOWN" state, and send alerts as configured: