Enter a domain and read the certificate its server actually presents: when it expires, how many days are left, who issued it and which names it covers.
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An SSL certificate (in practice a TLS certificate) is a small signed file a server presents at the start of every secure connection. It proves two things: that the name in the certificate matches the site you asked for, and that a certificate authority has checked that the applicant controls that name. It also carries the public key used to set up encryption, the name of the authority that issued it, and the dates between which it is valid.
The expiry date is the part that bites. A certificate is only trusted inside its validity window. The day it lapses, every browser treats the site as untrusted, however healthy everything else about the site is. That is why this checker leads with the expiry date and the days left: those two numbers decide whether a site keeps loading normally or falls off a cliff.
Browsers block the site with a full-page warning such as "Your connection is not private" and tell visitors the certificate has expired. Most people go back rather than click through, so traffic, sign-ups and sales fall off a cliff within hours. Nothing about the site itself has changed; only the date on the certificate has passed. The fix is a renewed certificate, and it works the moment it is installed, but every hour until then is lost traffic and lost trust.
Most certificates today last 90 days to about a year. The industry has been shortening lifetimes for years, because a short-lived certificate does less damage if its key leaks, and because frequent renewal forces automation. Auto renewal is the norm: hosts and services like Let's Encrypt renew in the background and swap the certificate before it expires. Expired-certificate outages now almost always mean the automation broke, a server was rebuilt by hand, or a certificate on a forgotten subdomain or mail host was never put on auto renewal at all.
Check google.com and this checker reports a certificate issued by Google Trust Services that covers google.com and its listed names, valid for about three months and renewed well before expiry, which is what a healthy setup looks like. Check an expired test certificate such as expired.badssl.com and the same checker reports it as expired with negative days left, because it reads the certificate the server actually presents instead of trusting that the connection worked.
See which authorities may issue for a domain with the CAA Record Checker. For the wider picture, run the Domain Health Checker. If a site moved, follow it with the Redirect Checker, and confirm a change has spread with the DNS Propagation Checker.
Enter the domain in this checker. It connects to the server on port 443, reads the certificate presented and shows the exact expiry date and how many days are left. You can also click the padlock in a browser and open the certificate details, but a checker is faster and works for sites you cannot open.
Browsers stop trusting the site and show a full-page warning before letting anyone in. Most visitors leave, so traffic and conversions drop sharply until the certificate is renewed and installed. The site itself is unchanged; only the certificate's validity window has ended.
Most last between 90 days and about a year. Free certificates from Let's Encrypt last 90 days, and many paid certificates are now sold with one-year terms. Short lifetimes are deliberate: they limit the damage from a leaked key and push everyone toward automatic renewal.
The subject is who the certificate is about: the domain name it covers. The issuer is the certificate authority that signed it and vouches for it. Browsers trust an issuer because it sits in their built-in trust store, and they trust the subject because a trusted issuer signed it.
SANs are the Subject Alternative Names: the full list of DNS names a certificate is valid for. One certificate can cover a domain, its www name and several subdomains or related domains. If a name is not in the SAN list, browsers reject the certificate for that name even if everything else is fine.
No. A self-signed certificate still encrypts the connection, but nobody has vouched for it, so browsers show a warning and visitors cannot tell your real site from a copy. Self-signed certificates are fine for private testing and internal systems. A public website needs a certificate from a trusted authority, which is free from issuers like Let's Encrypt.
Common reasons are that the certificate has expired, it is self-signed, it was issued for a different name than the one visited, the chain of issuers is incomplete, or the issuing authority is not in the browser's trust store. This checker helps you separate these: it shows the dates, the issuer and the covered names from the certificate itself.
Most hosts renew automatically, and Let's Encrypt certificates renew with a timer or a cron job using tools such as Certbot. If yours is not automatic, request a new certificate from your issuer or host, install it on the server and restart or reload the web service. Then run the domain through this checker to confirm the new expiry date is live.
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