An SSL certificate (more accurately a TLS certificate — SSL is the older name that stuck) enables encrypted HTTPS communication between a user's browser and a web server. It does two things:

‍Encryption — scrambles data in transit so it can't be read by anyone intercepting the connection.

‍Identity verification — proves that the server you're connecting to is actually who it claims to be, not an impostor.Certificates are issued by Certificate Authorities (CAs) — trusted third parties like Let's Encrypt, DigiCert, and Sectigo. When your browser connects to a site, it checks that the certificate was issued by a CA it trusts, the domain matches, and the certificate hasn't expired.

Types of SSL/TLS certificates:

DV (Domain Validated)
‍Confirms domain ownership only. Fast and cheap (Let's Encrypt is DV). Suitable for most sites.

OV (Organization Validated)
Verifies the organization behind the domain. Common for business sites.

‍EV (Extended Validation)
the highest level; requires rigorous identity checks. Used by banks and large enterprises.

A certificate chain is a sequence of certificates that links your website's certificate back to a root Certificate Authority (CA) that browsers trust.The chain has three levels:

‍Leaf certificate (your site's certificate) — issued directly to your domain.

‍Intermediate certificate(s) — issued by the root CA to an intermediate CA, which then issues certificates to websites. This keeps the root CA offline and protected.

‍Root certificate — self-signed by a trusted CA. Pre-installed in browsers and operating systems.

‍Why does this matter?
If the intermediate certificate is missing from the server's configuration, browsers can't verify the chain and will show a security error — even if your leaf certificate is perfectly valid. This is one of the most common SSL configuration mistakes. Our checker visualizes the full chain so you can spot gaps instantly.

Let's Encrypt certificates expire every 90 days (auto-renewing). Paid CA certificates typically last 1–2 years. Since September 2020, the maximum validity period for publicly trusted certificates is 398 days. Apple and Google are pushing toward 90-day maximums industry-wide.

What happens when an SSL certificate expires?

Browsers immediately show a "Your connection is not private" error and block users from reaching the site. This is why monitoring expiry dates matters.

SSL (Secure Sockets Layer) is the original protocol, now deprecated. All versions of SSL have known security vulnerabilities. TLS (Transport Layer Security) is its successor and what all modern HTTPS connections actually use — TLS 1.2 and TLS 1.3.

The term "SSL certificate" is still widely used, but technically every certificate in use today is a TLS certificate. When people say "SSL checker", they mean checking the TLS certificate on a server. This tool checks both — it reports the TLS version negotiated and the certificate details.