SSL Certificate Checker

An SSL certificate checker inspects the certificate a domain serves over HTTPS: is it valid, who issued it, when does it expire, does it match the domain, and is the chain complete. It answers both routine questions ("when does my cert renew?") and emergencies ("why are visitors seeing security warnings?").

Certificates are the trust layer of HTTPS — the padlock. An expired, mismatched or mis-chained certificate throws full-screen browser warnings that stop nearly all visitors cold, which makes expiry the most preventable outage on the web.

Enter a domain and read its certificate's facts: validity status, expiry date and days remaining, issuer (Let's Encrypt, DigiCert…), covered names (the domain and SANs), and chain completeness.

The checks that matter: expiry monitoring — modern certs run short (Let's Encrypt 90 days, paid certs 1 year max since 2020) and auto-renewal fails silently more often than anyone admits; checking your domains monthly (or before campaigns) catches the lapse before Chrome announces it; post-setup verification — after installing or renewing, confirm the new cert is actually being served (the classic: renewed but not reloaded); mismatch diagnosis — warnings on www vs non-www usually mean the cert covers one but not both; and chain issues — works-in-Chrome-fails-on-Android is the fingerprint of a missing intermediate certificate.

Context for Cloudflare-fronted sites: visitors see Cloudflare's edge certificate — fine and auto-renewed — while the origin cert behind it is a separate thing your host manages.