SSL/TLS Certificates Explained: Types, Validation & How to Check (2026)

Every time you visit a website that starts with https://, your browser is using an SSL/TLS certificate to establish an encrypted connection. These certificates are the foundation of web security, protecting everything from login credentials and payment details to email traffic and API calls. In 2026, running a website or mail server without a valid TLS certificate is not just a security risk — it signals to browsers, search engines, and users that your site cannot be trusted.

What Is SSL/TLS and How Does It Work?

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols that encrypt communication between a client and a server. SSL is the older protocol and has been deprecated since 2015; TLS 1.2 and TLS 1.3 are the current standards. Despite this, the term “SSL certificate” persists in common usage, even though modern certificates are technically TLS certificates.

When your browser connects to a server over HTTPS, a process called the TLS handshake occurs. The server presents its certificate, which contains its public key and identity information. The browser verifies that the certificate was issued by a trusted Certificate Authority (CA), checks that it has not expired or been revoked, and confirms that the domain name matches. If everything checks out, the browser and server negotiate an encryption key and begin transmitting data securely.

This entire process happens in milliseconds. TLS 1.3, the latest version, reduces the handshake to a single round trip, making encrypted connections nearly as fast as unencrypted ones.

DV, OV, and EV: Certificate Validation Levels

Not all SSL/TLS certificates are created equal. They come in three validation levels, each requiring a different degree of identity verification from the Certificate Authority.

Domain Validation (DV) is the most basic type. The CA only verifies that you control the domain, typically through a DNS record, an email to the domain owner, or an HTTP challenge file. DV certificates are issued within minutes and are free from providers like Let's Encrypt. They are suitable for blogs, personal sites, and any application where organizational identity verification is not required.

Organization Validation (OV) adds a layer of identity checking. The CA verifies that the organization behind the domain legally exists by checking business registrations and contact information. OV certificates typically take one to three days to issue and cost between $50 and $200 per year. They are common for business websites and SaaS applications.

Extended Validation (EV) is the most rigorous level. The CA performs extensive background checks, including legal existence, physical address, and operational status of the organization. EV certificates previously showed a green address bar in browsers, but most browsers have moved away from this visual indicator. They remain valuable for financial institutions, e-commerce platforms, and any organization where maximum trust is critical. EV certificates cost $100 to $500 or more per year.

How to Check an SSL/TLS Certificate

You can inspect any website's certificate by clicking the padlock icon in your browser's address bar, but for a detailed technical analysis, use our SSL Checker. It shows the certificate issuer, expiration date, key size, signature algorithm, certificate chain, and whether the server supports TLS 1.2 and TLS 1.3.

Key things to check include: the certificate has not expired, it covers the correct domain (including subdomains if using a wildcard), the certificate chain is complete (no missing intermediate certificates), and the server does not support deprecated protocols like SSL 3.0 or TLS 1.0. A broken certificate chain is one of the most common causes of SSL errors, because the server fails to send the intermediate certificate that links the site's certificate to the trusted root CA.

Common SSL/TLS Errors and How to Fix Them

ERR_CERT_DATE_INVALID: The certificate has expired. Renew it immediately through your CA or hosting provider. If you use Let's Encrypt, ensure your auto-renewal cron job or Certbot timer is running correctly.

ERR_CERT_COMMON_NAME_INVALID: The domain in the certificate does not match the URL. This often happens when accessing a site via www.example.com but the certificate only covers example.com, or vice versa. Use a certificate that includes both, or add a Subject Alternative Name (SAN).

ERR_CERT_AUTHORITY_INVALID: The browser does not trust the certificate's issuer. This can happen with self-signed certificates or when the intermediate certificate is missing from the server configuration. Make sure your server sends the full certificate chain.

Mixed content warnings: The page loads over HTTPS but includes resources (images, scripts, stylesheets) over HTTP. Update all resource URLs to use HTTPS or protocol-relative paths.

Let's Encrypt vs Paid Certificate Authorities

Let's Encrypt is a free, automated, and open Certificate Authority that has issued billions of certificates since its launch in 2016. It provides DV certificates that are technically identical in encryption strength to paid alternatives. For most websites, Let's Encrypt is the right choice. Certificates are valid for 90 days and are designed to be renewed automatically using tools like Certbot.

Paid CAs like DigiCert, Sectigo, and GlobalSign offer OV and EV certificates, longer validity periods (up to one year in 2026, down from the previous two years), warranty coverage, and dedicated support. Choose a paid CA when you need organization validation, EV verification, or enterprise support SLAs.

The Certificate Chain Explained

A certificate chain (or chain of trust) links your site's certificate to a root CA that browsers inherently trust. The chain typically has three levels: the root CA certificate (pre-installed in browsers and operating systems), an intermediate CA certificate (used by the root CA to delegate signing), and your end-entity (leaf) certificate. Your server must send both the leaf and intermediate certificates during the TLS handshake. The root certificate is not sent because the browser already has it. Use our SSL Checker to verify that your chain is complete.

Certificate Renewal and Automation

Certificate expiration is one of the most common causes of website outages. In 2026, maximum certificate lifetimes are one year for paid certificates and 90 days for Let's Encrypt. Automate renewal wherever possible. Most hosting providers and CDNs (Vercel, Cloudflare, AWS) handle certificate provisioning and renewal automatically. If you manage your own server, set up Certbot with a cron job or systemd timer and test renewal with certbot renew --dry-run.

SSL/TLS and Your Overall Security Posture

A valid TLS certificate is just one piece of your security infrastructure. Check your HTTP security headers with our HTTP Headers Checker to ensure you have HSTS, Content-Security-Policy, and other protective headers in place. Run a full Domain Health Check to see how your certificate, DNS, and email authentication all work together.

For more on how email security and DNS fit into the bigger picture, read our Email Deliverability Guide and our DNS Record Types Explained article.