What is SSL / TLS?

Transport Layer Security (TLS) is the encryption protocol that protects web traffic. TLS is the successor to SSL (Secure Sockets Layer), though people still say SSL colloquially. TLS 1.2 and 1.3 are the current versions; TLS 1.0 and 1.1 are deprecated and should be disabled.

In more detail

TLS does three things: it encrypts the connection so eavesdroppers cannot read traffic, it authenticates the server with a certificate, and it ensures traffic is not tampered with. A misconfigured TLS setup (expired certificate, weak ciphers, old protocol version) can fail any of these.

Most managed platforms (Vercel, Cloudflare, Netlify) handle TLS automatically with free certificates from Let's Encrypt. Self-hosted deployments need certbot or similar to keep certificates fresh.

Why this matters

Why builders care

An expired certificate breaks your site — every browser shows a full-screen warning. For managed hosts this is rare, but custom domain setups can fail silently. Use a monitoring tool to alert you 14+ days before expiry.

Fix guides

Fix SSL / TLS issues

Expired SSL certificate

An expired certificate breaks your site — browsers show a big red warning. Here is how to renew and set up auto-renewal.

Weak SSL cipher

TLS 1.0, TLS 1.1, or weak ciphers like RC4 or 3DES are vulnerable. Here is how to force modern TLS on Vercel, Cloudflare, and self-hosted servers.

Mixed content warnings

Loading HTTP resources from an HTTPS page breaks the security guarantee. Browsers block most of it automatically now — here is how to fix the rest.

Free tools

Check it yourself

SSL checker

Certificate validity, TLS version, and cipher strength — in 10 seconds.

Related terms

Keep learning

HTTP Strict Transport Security

HSTS is an HTTP response header that tells browsers to only connect to your site over HTTPS, even if a user types `http://`. It stops SSL stripping attacks.

Mixed Content

When an HTTPS page loads resources over HTTP, breaking the HTTPS guarantee. Browsers block most of it automatically.

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