TLS ALPN Negotiation

Test Application-Layer Protocol Negotiation (ALPN) to see which protocol a server selects from your offered list. Commonly used to negotiate HTTP/2, HTTP/3, or other application protocols during TLS handshake.

ALPN Examples

ALPN Negotiation Configuration

Quick select:

Understanding ALPN

What is ALPN?

Application-Layer Protocol Negotiation (ALPN) is a TLS extension that allows the client and server to negotiate which application protocol to use during the TLS handshake.

Common Protocols

  • h2: HTTP/2 - Binary, multiplexed protocol
  • h3: HTTP/3 - Latest HTTP over QUIC
  • http/1.1: Traditional HTTP/1.1
  • spdy/3.1: Legacy SPDY protocol

Protocol Priority

Protocols are offered in preference order. The server selects the first protocol from your list that it supports. Order matters!