Source: https://uptimeify.io/resources/platform-and-support/glossary/tls-handshake

# TLS Handshake

> The TLS handshake is the negotiation at the start of an HTTPS connection where client and server agree on encryption and the server proves its identity with a certificate.

A slow or failing handshake, caused by an expired certificate, an incomplete chain, or a protocol mismatch, blocks the connection before any content loads. It is a common, hard-to-spot cause of "the site is down".