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SSL Certificate Checker: How to Verify Website Security

Learn how to read SSL certificates, spot security issues, and understand why HTTPS is non-negotiable in 2026.

Security Tools 2026-04-09 By Risetop Team 11 min read

That little padlock icon in your browser's address bar represents the foundation of web security. Behind it is an SSL/TLS certificate — a digital document that proves a website's identity and enables encrypted communication. But do you know what that certificate actually says, whether it's properly configured, or what happens when it expires?

This guide teaches you how to check SSL certificates, interpret the details, identify common problems, and keep your own website's encryption up to standard.

What Is an SSL Certificate?

An SSL certificate (technically a TLS certificate — SSL is the older, deprecated protocol) is a digital certificate that binds a cryptographic key to an organization's details. When installed on a web server, it activates the HTTPS protocol and enables encrypted connections between the server and the user's browser.

Without SSL/TLS, data travels between your browser and the server in plaintext. Anyone on the same network — at a coffee shop, office, or ISP level — can read everything: passwords, credit card numbers, personal messages, search queries.

⚠️ HTTP is not safe: Any website that still uses HTTP (no padlock) is transmitting all data unencrypted. Google Chrome labels these sites as "Not Secure," and search engines penalize them in rankings.

How SSL/TLS Works (Simplified)

When you visit an HTTPS website, this happens in milliseconds:

  1. TLS Handshake: Your browser contacts the server and they negotiate an encryption protocol and cipher suite.
  2. Certificate Exchange: The server sends its SSL certificate to your browser.
  3. Verification: Your browser checks the certificate against a list of trusted Certificate Authorities (CAs). If the certificate was issued by a trusted CA and hasn't expired, the connection proceeds.
  4. Key Exchange: The browser and server agree on a session key using asymmetric encryption (the certificate's public key). This key encrypts all subsequent communication using fast symmetric encryption.
  5. Encrypted Session: All data between you and the server is encrypted. Even if intercepted, it appears as unreadable ciphertext.

Types of SSL Certificates

By Validation Level

Type Verification Time Cost Best For
DV (Domain Validation) Domain ownership only Minutes Free - $50/yr Personal sites, blogs, basic security
OV (Organization Validation) Domain + organization identity 1-3 days $50-200/yr Businesses, e-commerce
EV (Extended Validation) Domain + organization + legal/physical verification 3-7 days $150-500/yr Financial institutions, enterprises

Important: all three types provide the same level of encryption. The difference is in identity verification, not encryption strength. A free DV certificate from Let's Encrypt encrypts data just as well as a $500 EV certificate.

By Coverage

How to Check an SSL Certificate

Method 1: Browser (Quick Check)

  1. Visit the website in your browser
  2. Click the padlock icon in the address bar
  3. Click "Connection is secure" → "Certificate is valid"
  4. View the certificate details: issuer, validity dates, and domain coverage

This gives you basic information but doesn't show the full picture — certificate chain status, cipher suite, or protocol version.

Method 2: Online SSL Checker (Recommended)

For a comprehensive analysis, use our SSL Certificate Checker Tool. It shows:

Method 3: Command Line

# Check certificate details with openssl openssl s_client -connect example.com:443 -servername example.com /dev/null | openssl x509 -noout -text # Check expiration date echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates # Check certificate chain openssl s_client -connect example.com:443 -showcerts

Key Certificate Details to Check

1. Validity Period

Every certificate has a Not Before and Not After date. Certificates issued after September 2020 have a maximum validity of 398 days (about 13 months), per CA/Browser Forum rules. Many CAs now default to 90-day or 1-year certificates.

If a certificate has expired, browsers will display a full-page warning. Users must explicitly click through to proceed — most won't.

2. Domain Coverage (SAN)

The certificate's Subject Alternative Name (SAN) field lists all domains the certificate covers. If you're accessing blog.example.com but the certificate only covers example.com, the browser will show a name mismatch error.

⚠️ Common Name is deprecated: Older certificates used the CN (Common Name) field for domain matching. Modern certificates must use the SAN field. If a certificate has no SAN, browsers will reject it.

3. Certificate Chain

An SSL certificate doesn't work alone — it's part of a chain of trust:

  1. Root Certificate: Self-signed certificate from a trusted CA, pre-installed in browsers and operating systems
  2. Intermediate Certificate(s): Bridge between the root and your server's certificate
  3. Server Certificate: The certificate for your specific domain

If the server doesn't send the intermediate certificates, the browser can't build the chain to a trusted root — even though your certificate is valid. This is one of the most common SSL configuration errors.

4. Protocol and Cipher Suite

The TLS protocol version and cipher suite determine the strength of encryption:

  • TLS 1.3: ✅ Current standard. Fast, secure, modern ciphers only.
  • TLS 1.2: ✅ Acceptable with proper cipher configuration.
  • TLS 1.0 / 1.1: ❌ Deprecated and disabled in all modern browsers (2020-2021).
  • SSLv3: ❌ Completely broken. Vulnerable to POODLE attack.

Common SSL Problems and Solutions

Problem: "NET::ERR_CERT_AUTHORITY_INVALID"

Cause: The certificate was issued by a CA that isn't trusted by the browser. This usually means a self-signed certificate or an incomplete chain.

Fix: Use a certificate from a trusted CA (Let's Encrypt is free). If you're using a trusted CA, ensure all intermediate certificates are installed on the server.

Problem: "NET::ERR_CERT_DATE_INVALID"

Cause: The certificate has expired or the server clock is wrong.

Fix: Renew the certificate. Set up automatic renewal (certbot for Let's Encrypt). Verify the server's system clock is accurate.

Problem: "NET::ERR_CERT_COMMON_NAME_INVALID"

Cause: The certificate doesn't cover the domain you're accessing.

Fix: Get a certificate that includes the correct domain in its SAN. For multiple subdomains, use a wildcard certificate.

Problem: Mixed Content Warning

Cause: An HTTPS page loads resources (images, scripts, CSS) over HTTP. The padlock may appear broken or show "Not Secure."

Fix: Update all resource URLs to use HTTPS or relative paths. Use the browser's Developer Tools Console to find mixed content warnings.

Getting a Free SSL Certificate (Let's Encrypt)

Let's Encrypt provides free, trusted SSL certificates with automated renewal. It's the most popular choice for websites worldwide, with over 400 million active certificates.

# Install certbot (Ubuntu/Debian) sudo apt install certbot python3-certbot-nginx # Get a certificate for your domain sudo certbot --nginx -d example.com -d www.example.com # Test automatic renewal sudo certbot renew --dry-run # For non-nginx setups sudo certbot certonly --standalone -d example.com
💡 Auto-renewal: Certbot automatically installs a cron job or systemd timer for renewal. Certificates are valid for 90 days, and certbot renews them at 30 days before expiry. Verify renewal is working with sudo certbot renew --dry-run.

SSL for Developers

If you're developing locally, you need HTTPS too — many APIs (geolocation, camera, service workers) require a secure context.

# Generate a self-signed certificate for local development openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days 365 -nodes # Or use mkcert for trusted local certificates mkcert -install mkcert localhost 127.0.0.1 ::1

For Node.js development, set NODE_OPTIONS=--use-openssl-ca or configure your server to use the generated certificates.

SSL Monitoring and Best Practices

  • Set up expiry alerts: Don't wait until your certificate expires. Set up monitoring to alert you 30 days before expiry.
  • Use certificate transparency logs: Monitor CT logs to detect unauthorized certificates issued for your domain (potential phishing or MITM attacks).
  • Enable HSTS: Add the Strict-Transport-Security header to force browsers to always use HTTPS for your site.
  • Disable old protocols: Only allow TLS 1.2 and TLS 1.3. Disable SSLv3, TLS 1.0, and TLS 1.1.
  • Use strong cipher suites: Prefer AES-GCM and ChaCha20 ciphers. Disable RC4, DES, and export-grade ciphers.

Check any website's SSL certificate instantly with our free SSL Certificate Checker Tool — detailed analysis including chain status, cipher suite, and expiry countdown.

Conclusion

SSL/TLS certificates are the backbone of web security. Every website should use HTTPS — it's no longer optional. Free certificates from Let's Encrypt make this accessible to everyone, and automated tools like certbot eliminate the maintenance burden.

Whether you're a website owner ensuring your visitors are protected, a developer debugging HTTPS issues, or a security-conscious user verifying that a site is safe to use, understanding SSL certificates is an essential skill. Use an SSL checker regularly to catch problems before your users do.