What is an SSL/TLS certificate?
An SSL/TLS certificate is what lets a browser connect to your site over HTTPS and show the padlock. It proves the site is who it claims to be and encrypts the traffic in between. Every certificate is issued for a fixed window with a hard expiry date — and the day it lapses, browsers stop trusting it and start showing full-page security warnings.
Why certificates expire so often
Modern certificates are deliberately short-lived. Let's Encrypt issues 90-day certificates, and the industry is moving toward even shorter lifetimes. That's good for security, but it means renewal has to happen many times a year — usually automatically. The checker shows you the current window and how close the next deadline is.
What the checker shows you
- Issuer — the certificate authority that signed it (e.g. Let's Encrypt, Google Trust Services, DigiCert).
- Valid from / valid to — the exact start and end of the certificate's life.
- Days left — the countdown that actually matters.
- Chain — whether intermediates are present so browsers can build a path to a trusted root.
Common SSL errors — and what causes them
An expired certificate is the most common and the most damaging. A hostname mismatch happens when the certificate doesn't cover the exact domain (for example it covers example.com but not www.example.com). An incomplete chain works in some browsers but fails in others. A self-signed certificate isn't trusted by anyone but you. Each of these shows up as a scary warning to visitors even when the server itself is running fine.
Why "auto-renewal" isn't a guarantee
Most teams assume renewal is handled — until it isn't. A renewal job silently stops, a validation step breaks after a DNS change, or a new subdomain is added that the certificate never covered. Because the server keeps responding, uptime checks stay green and nobody notices until the certificate is already expired.
From a one-off check to daily monitoring
Checking once tells you today's status; it can't warn you about the renewal that fails next month. SSL certificate monitoring in Domain Monitor Hub checks your certificates every day and alerts you well before expiry — with a "Check SSL now" button for instant re-checks. Check a host here; let the app keep the padlock green for you.