SSL Certificate Checker
Check SSL/TLS certificate details for any domain. View the issuer, validity period, subject alternative names, and full certificate chain.
About SSL/TLS certificates
An SSL/TLS certificate proves that a website is who it claims to be and lets browsers establish an encrypted HTTPS connection. Modern browsers visually mark sites without a valid certificate as "Not Secure," and search engines factor HTTPS into ranking. This tool fetches the live certificate served by any domain on port 443 and shows the issuing CA, validity window, signature algorithm, subject alternative names, and the full certificate chain back to the trusted root.
Use it to verify a freshly-installed certificate, debug "your connection is not private" errors, audit which subdomains are covered by a wildcard SAN, or watch expiration dates before they cause an outage. Most public CAs (Let’s Encrypt, Google Trust Services, DigiCert, Sectigo) issue certificates valid for 90 days or less, so monitoring expiry is a routine ops task.
Frequently asked questions
What is an SSL/TLS certificate?
A digital file issued by a Certificate Authority that binds a domain name to a public key. It enables HTTPS encryption and proves the domain's identity to a visitor's browser.
How can I check if a website's SSL certificate is valid?
Enter the domain in the form above. The tool connects over HTTPS, parses the certificate, and reports whether it's currently within its validity window, who issued it, and how many days remain before expiration.
Why is my certificate showing as expired or invalid?
Common causes are an expired Not After date, a hostname that does not match any of the certificate's Subject Alternative Names, an incomplete chain that is missing the intermediate certificate, or a self-signed certificate that browsers do not trust.
What is a certificate chain?
Every leaf certificate is signed by an intermediate CA, which is in turn signed by a root CA. Browsers only trust the roots, so the server must serve the leaf plus all intermediates so a continuous chain to a trusted root can be built.