SSL Certificate Checker
Check the SSL certificate of any website: expiry date with a live countdown, issuer, trust status, TLS version and every domain the certificate covers.
What this SSL checker shows you
The checker opens a real TLS connection to your domain on port 443, exactly like a browser does, and reads the certificate the server sends back. You get the certificate authority that issued it, the valid-from and valid-to dates, a countdown of days until expiry, the negotiated TLS version and cipher, the SHA-256 fingerprint, and the full list of Subject Alternative Names, the domains and wildcard subdomains the certificate actually covers.
It also runs a strict trust verification and reports the exact failure class when one exists: expired, not yet valid, hostname mismatch, self-signed, or a missing intermediate certificate. Honesty note: the verification uses this checker's own trust store (OpenSSL on our server), which closely tracks but is not identical to Chrome, Firefox or Safari; hostname matching follows RFC 6125 with SAN precedence, so a certificate that only matches via its legacy Common Name is correctly reported as one browsers will reject. Every validated server address is tested, so an IPv4/IPv6 split or a broken CDN edge shows up instead of depending on which address the checker happened to pick.
Why SSL expiry monitoring matters
Certificate expiry is one of the most common self-inflicted outages on the web. Most certificates now last only 90 days, renewal automation fails quietly, and the first sign is usually a customer screenshot of a browser warning. Checking manually helps today; knowing before it happens is better. DevDome Site Health watches your certificates and uptime around the clock on every site you connect.
SSL checker FAQ
How do I check the SSL certificate of a website?
Enter the domain above and the checker connects to the site on port 443, reads the certificate the server presents, and shows the issuer, the validity window, the exact days until expiry, the TLS version, the covered domain names and whether browsers trust the certificate chain.
What happens when an SSL certificate expires?
Browsers show a full-page security warning like NET::ERR_CERT_DATE_INVALID and most visitors leave immediately. Payments, logins, APIs and webhooks that call your site also start failing, so an expired certificate is effectively downtime for the whole site.
How often do SSL certificates need to be renewed?
Most certificates today are issued for 90 days (Let's Encrypt, Google Trust Services, ZeroSSL) and are renewed automatically by the server or CDN. Paid certificates are typically valid for one year. If your certificate shows fewer than 14 days left and you did not expect that, check your auto-renewal now.
Why does the checker say the certificate is not trusted?
A certificate can be untrusted because it expired, because it was issued for different domain names than the one you are visiting, because it is self-signed, or because the server does not send the intermediate certificate that links it to a trusted authority. The details above show which of these applies.
What are SANs on an SSL certificate?
Subject Alternative Names are the list of domains one certificate covers. A certificate for example.com often also covers www.example.com, and a wildcard entry like *.example.com covers every direct subdomain. If your domain is not in the SAN list, browsers reject the connection.
Why do different SSL checkers show different expiry dates for the same domain?
Many sites, especially those behind CDNs like Cloudflare, serve two certificates for the same hostname: a modern ECDSA certificate and a separate RSA certificate for older clients. Each has its own issuer, serial number and expiry date. Which one a checker reports depends on the TLS handshake it performs. This tool performs both handshakes and shows you both certificates when they differ.
Does SSL affect SEO?
Yes. HTTPS has been a Google ranking signal since 2014, Chrome marks plain HTTP pages as Not Secure, and an expired certificate interrupts crawling and indexing while it is broken. Keeping a valid certificate is table stakes for both rankings and trust.
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