Every time you visit a website, your browser checks that site's SSL/TLS certificate. This certificate is what enables the padlock icon in your address bar and the https:// prefix in the URL. It proves that the website is who it claims to be and that your connection is encrypted.

But what happens when a certificate expires, is misconfigured, or was issued by an untrusted authority? Your browser might show a stark warning page — or worse, visitors might not notice subtle security issues. Our SSL Certificate Checker lets you inspect any domain's certificate details instantly.

What Is an SSL/TLS Certificate?

An SSL (Secure Sockets Layer) or TLS (Transport Layer Security) certificate is a digital document that binds a cryptographic key to an organization's details. When installed on a web server, it activates the padlock and enables encrypted connections.

What a Certificate Contains

Subject — The domain name (Common Name or CN) and additional Subject Alternative Names (SANs)
Issuer — The Certificate Authority (CA) that issued the certificate (e.g., Let's Encrypt, DigiCert, Sectigo)
Validity Period — Not Before and Not After dates defining when the certificate is active
Public Key — The cryptographic key used to establish encrypted connections
Signature Algorithm — The algorithm used to sign the certificate (e.g., SHA-256 with RSA)
Fingerprints — SHA-1 and SHA-256 hash values that uniquely identify the certificate
Certificate Chain — The hierarchy from the server certificate up to the root CA

Why Certificate Checking Matters

Expired Certificates

An expired certificate causes browsers to display security warnings. Visitors may leave immediately — studies show that over 80% of users abandon a site after seeing a certificate warning. For e-commerce sites, this translates directly to lost revenue.

Misconfigured Chains

A certificate chain is the path from your server certificate through intermediate certificates to a root CA trusted by browsers. If intermediate certificates are missing, some browsers may trust the connection while others don't, causing intermittent errors that are difficult to diagnose.

Revoked Certificates

Certificates can be revoked before their expiration date if the private key is compromised or the certificate was issued incorrectly. Checking revocation status ensures the certificate is still considered valid by its issuer.

Weak Algorithms

Older certificates may use deprecated algorithms like SHA-1 (collision-prone) or RSA with 1024-bit keys (too short for modern security). Today's minimum standard is SHA-256 signatures with 2048-bit RSA keys or ECDSA equivalents.

How to Check an SSL Certificate

Using our SSL Certificate Checker, you can inspect any publicly accessible HTTPS domain in seconds:

Enter the domain name (e.g., example.com — no https:// needed)
The tool fetches the certificate details directly from the server
Results display issuer, validity period, certificate chain, and more

What to Look For

Check	What's Healthy	Red Flag
Expiration	More than 30 days until expiry	Expired or expiring within 7 days
Issuer	Recognized CA (Let's Encrypt, DigiCert, etc.)	Self-signed or unknown issuer
Chain	Complete chain to trusted root	Missing intermediate certificates
Algorithm	SHA-256 or better	SHA-1 or MD5 signatures
Key Strength	RSA 2048+ bits or ECDSA	RSA 1024 bits or lower

Types of SSL Certificates

Domain Validation (DV)

The most common and basic level. The CA verifies only that you control the domain (usually via email or DNS record). DV certificates are issued automatically and quickly — Let's Encrypt issues them for free.

Organization Validation (OV)

The CA verifies your organization's legal existence and physical address. OV certificates show company details in the certificate info, providing moderate trust for business websites.

Extended Validation (EV)

The highest level of validation. The CA conducts a thorough vetting of your organization's legal, physical, and operational existence. EV certificates historically turned the address bar green (most browsers now show the organization name). They're preferred for banks, government sites, and major e-commerce platforms.

Certificate Lifecycle Management

Effective certificate management involves:

Monitoring — Track expiration dates across all domains. Many organizations manage hundreds or thousands of certificates.
Renewal — Let's Encrypt certificates expire after 90 days, requiring frequent automated renewal. Commercial certificates typically last 1-2 years.
Revocation — If a private key is compromised, revoke the certificate immediately and issue a replacement.
Inventory — Maintain a complete inventory of all certificates, including internal and development servers.

Certificate management is one of the most overlooked aspects of web security. A forgotten certificate can take down production systems with little warning.

Common SSL/TLS Issues and Fixes

Certificate Name Mismatch

The certificate's Common Name or SANs don't cover the requested domain. Fix: ensure all domain variants (www and non-www, subdomains) are included in the certificate.

Self-Signed Certificate

The certificate is signed by itself rather than a trusted CA. Fix: use a publicly trusted CA like Let's Encrypt for public sites, or add the self-signed certificate to internal trust stores for development.

Expired Certificate

The current date is past the Not After date. Fix: renew the certificate immediately. Most CAs send renewal reminders 30 days before expiry.

Incomplete Chain

The server didn't send required intermediate certificates. Fix: configure your web server to serve the full certificate chain. Most CAs provide a chain file or bundle.

SSL/TLS Best Practices

Use automated certificate management — Certbot and other ACME clients handle Let's Encrypt renewal automatically.
Monitor certificate expiry — Set alerts at 30, 14, and 7 days before expiration.
Deploy modern protocols — TLS 1.2 and 1.3 only. Disable SSL 3.0, TLS 1.0, and TLS 1.1.
Use strong key exchange — Prefer ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) for forward secrecy.
Enable HSTS — HTTP Strict Transport Security tells browsers to always connect via HTTPS.
Check your configuration — Use tools like our SSL Certificate Checker to validate your setup.

Try It Now

Check any domain's SSL certificate immediately with the SSL Certificate Checker. No registration needed, no data stored — your domain lookups are private and processed entirely client-side.

Related Tools

HTTP Headers Inspector — Inspect security and response headers
CORS Header Tester — Debug cross-origin resource sharing
Password Generator — Create strong, unique passwords
Hash Generator — Compute SHA and MD5 hashes

SSL Certificate Checker: Verify TLS Certificates & Stay Secure Online