Our free SSL certificate checker connects to any domain and examines its TLS certificate in detail. Enter a domain name to check certificate validity, expiration date, issuer, subject alternative names, certificate chain, and the TLS protocol version in use. This SSL certificate checker helps webmasters monitor certificate health, diagnose HTTPS issues, and verify that their TLS configuration meets current security standards.

What Is an SSL/TLS Certificate?

An SSL/TLS certificate is a digital certificate that authenticates a website’s identity and enables encrypted communication between the browser and server. When you see the padlock icon in your browser’s address bar, it means the site has a valid SSL certificate and your connection is encrypted. Despite the common name “SSL,” modern certificates use TLS (Transport Layer Security), the successor to the deprecated SSL protocol.

What Does This Tool Check?

Our SSL certificate checker connects to a domain on port 443 and examines the TLS handshake to retrieve detailed certificate information:

Certificate validity — Whether the certificate is currently valid, expired, or expiring soon
Subject and issuer — Who the certificate was issued to and by which Certificate Authority (CA)
Expiration dates — When the certificate was issued and when it expires, with a countdown of days remaining
Subject Alternative Names (SANs) — All domain names and subdomains covered by the certificate
Connection details — TLS protocol version, cipher suite, and key size used for the connection
Certificate chain — The full chain from the site’s certificate through intermediate CAs to the root CA

Why Monitor SSL Certificates?

Expired SSL certificates cause browser security warnings that drive visitors away and can break API integrations, webhook deliveries, and automated systems that rely on verified HTTPS connections. Running an SSL certificate checker on a regular schedule helps you catch expiring certificates before they cause downtime. Most Certificate Authorities recommend renewing at least 30 days before expiration. Let’s Encrypt certificates, which are free and widely used, expire every 90 days and should be auto-renewed.

Understanding the Certificate Chain

SSL certificates form a chain of trust: your site’s certificate (leaf) is signed by an intermediate CA, which is signed by a root CA that browsers inherently trust. A complete chain is essential — if any intermediate certificate is missing, some browsers and clients may reject the connection even if the leaf certificate itself is valid. This is one of the most common TLS configuration errors, and an SSL certificate checker makes it easy to verify that the full chain is served correctly.

Types of SSL Certificates

Certificates come in several validation levels:

Domain Validation (DV) — Verifies domain ownership only. Fast to issue, used by most websites. Let’s Encrypt issues DV certificates for free.
Organization Validation (OV) — Verifies the organization behind the domain. Shows company name in certificate details.
Extended Validation (EV) — The highest level, requiring thorough business verification. Previously displayed a green bar in browsers, though most browsers no longer differentiate visually.
Wildcard — Covers all subdomains of a domain (e.g., *.example.com). Useful for sites with many subdomains.
Multi-Domain (SAN) — Covers multiple distinct domain names in a single certificate using Subject Alternative Names.

TLS Protocol Versions

Modern websites should support TLS 1.2 or TLS 1.3. Older versions (TLS 1.0, TLS 1.1, SSL 3.0) have known vulnerabilities and are no longer considered secure — major browsers have dropped support for them. TLS 1.3 offers improved performance with fewer round trips during the handshake, perfect forward secrecy by default, and stronger cipher suites. Use the Mozilla SSL Configuration Generator to create a secure server configuration, then verify it with this SSL certificate checker to confirm your TLS setup is correct.

Certificate Transparency

Certificate Transparency (CT) is a system where CAs publicly log every certificate they issue. This helps domain owners detect unauthorized certificates issued for their domains (e.g., by a compromised CA). You can search CT logs to see all certificates ever issued for a domain, making it easier to spot potential security issues or unauthorized issuance.

Related Tools

After checking your SSL certificate, use our HTTP Header Checker to verify your HSTS and other security headers are properly configured. For domain registration details including expiry date, try our WHOIS Lookup.

SSL Certificate Checker