SSL Certificate Checker
What Is an SSL Certificate?
An SSL (Secure Sockets Layer) certificate is a digital credential that authenticates a website's identity and establishes an encrypted connection between the visitor's browser and the web server. When a website has a valid SSL certificate, the browser displays a padlock icon in the address bar and the URL starts with https:// instead of http://. This encryption ensures that sensitive data such as login credentials, payment information, and personal details cannot be intercepted by third parties.
SSL certificates are issued by Certificate Authorities (CAs) - trusted organizations that verify the identity of the certificate applicant. Popular CAs include Let's Encrypt (free, automated certificates), DigiCert, Sectigo, and GlobalSign. Each certificate contains the domain name, the issuing CA, the validity period, the public key, and digital signatures that browsers use to verify authenticity.
Modern websites actually use TLS (Transport Layer Security), the successor to SSL. TLS 1.2 and TLS 1.3 are the current standards, while older SSL versions have been deprecated due to known vulnerabilities. Despite this, the term "SSL certificate" remains widely used. Our checker connects to the target server, performs a TLS handshake, and inspects the certificate details including the issuer, validity dates, signature algorithm, and Subject Alternative Names (SANs).
Monitoring your SSL certificate is important for several reasons. An expired certificate triggers browser warnings that scare away visitors and hurt your search engine rankings. Google has confirmed that HTTPS is a ranking factor, and browsers like Chrome mark HTTP sites as "Not Secure." Our tool shows the exact number of days remaining before expiry, color-coded for quick assessment: green means more than 30 days, yellow means 7 to 30 days, and red means fewer than 7 days remaining.
Subject Alternative Names (SANs) allow a single certificate to cover multiple domains and subdomains. For example, a certificate for example.com might also include www.example.com, api.example.com, and mail.example.com. Checking SANs helps verify that all your domains are properly covered by your certificate. Use our HTTP Headers tool to verify your security headers, or check Certificate Transparency logs to see all certificates ever issued for your domain.
Frequently Asked Questions
What is an SSL certificate?
An SSL certificate is a digital certificate that authenticates a website's identity and enables an encrypted connection between the web server and the browser. When a site has a valid SSL certificate, the browser shows a padlock icon and the URL begins with https:// instead of http://.
How do I check if an SSL certificate is valid?
Enter the domain name in our SSL checker tool. It will connect to the server, inspect the TLS certificate, and show you the issuer, validity dates, days remaining until expiry, signature algorithm, and all domains covered by the certificate (SANs). A valid certificate should be issued by a trusted authority and not be expired.
What happens when an SSL certificate expires?
When an SSL certificate expires, browsers display a security warning to visitors, which can drive away traffic and hurt trust. Search engines may also lower rankings for sites with expired certificates. Most certificate authorities and hosting providers offer auto-renewal, but it is important to monitor expiry dates as a safety net.
What are Subject Alternative Names (SANs)?
Subject Alternative Names are additional domain names or subdomains covered by a single SSL certificate. For example, a certificate for example.com might also include www.example.com, api.example.com, and mail.example.com as SANs. This allows one certificate to secure multiple domains.
What is the difference between SSL and TLS?
TLS (Transport Layer Security) is the successor to SSL. Although people still say SSL, modern websites actually use TLS 1.2 or TLS 1.3 for encryption. The older SSL protocol versions (2.0 and 3.0) are deprecated due to known security vulnerabilities. Our checker verifies the current TLS certificate on the server.