What is SSL/TLS and Why Does It Matter?
SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) encrypt communication between browsers and servers. When you see the padlock icon in your browser's address bar, it means the connection is secured by a valid SSL/TLS certificate. Without it, data travels in plain text, vulnerable to interception and tampering.
How to Check SSL Certificates
You can check SSL certificate status in several ways: use this tool to quickly verify any domain, click the padlock icon in your browser for basic details, or use command-line tools like openssl s_client -connect domain.com:443 for full certificate chain information.
Key things to check: expiration date (certificates expire every 90 days with Let's Encrypt, or annually with paid CAs), domain name match (the certificate must cover the exact domain or use wildcards), and the certificate chain (all intermediate certificates must be properly installed).
Common SSL Certificate Errors
The most frequent SSL error is ERR_CERT_DATE_INVALID (expired certificate). This happens when auto-renewal fails silently, often due to DNS changes, firewall rules blocking the ACME challenge, or credential rotation breaking the renewal script. Other common errors include domain mismatches (wrong certificate installed) and incomplete certificate chains (missing intermediate certificates).
SSL Certificate Types Explained
Domain Validation (DV) certificates are the simplest, verifying only domain ownership. Let's Encrypt provides these for free. Organization Validation (OV) certificates add business identity verification. Extended Validation (EV) certificates require thorough business vetting and are used by financial institutions.
Preventing SSL-Related Outages
Expired SSL certificates cause immediate and total outages. Browsers show a full-page security warning that blocks most users from accessing your site. To prevent this: enable auto-renewal, monitor certificate expiry dates with at least 30 days of advance warning, and test renewal processes regularly. Certificate monitoring should be part of your uptime monitoring strategy, not an afterthought.