A valid certificate is what gives visitors the padlock and keeps the warning page away. Three things make it valid: it has not expired, it matches the address and a trusted authority signed it.
Every certificate has an end date. After that date, browsers show a warning, even though the site itself is running.
The certificate must list the address visitors use. A certificate for www.example.com does not automatically cover example.com.
Browsers accept certificates from authorities they trust. A self-made certificate, or one with a missing link in its chain, produces an error.
Click the padlock in the address bar and open the certificate details. You will see who it was issued to, who issued it and the dates. A look at the end date is worthwhile too.
Our free Website check reads the certificate of your website and tells you in plain words whether it looks fine. Open Website check
Last reviewed: 2026-11-02
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