demo · v143

WebTransport ALPN

Build a client and server protocol list. The simulator runs the v143 negotiation algorithm and shows the headers that would cross the wire, then attempts a real new WebTransport(url, {protocols}) against a URL you choose.

capability probes

negotiation simulator

client protocols (comma-sep, in priority order) server protocols (comma-sep, supported)

chosen protocols

wire (CONNECT request → settings frame)

attempt a real connection

WebTransport URL

click Connect. Most public endpoints reject random clients — the error itself is informative.

the call

// v143: pass an ordered list of application protocols
const wt = new WebTransport("https://example.com/", {
  protocols: ["my-app/2", "my-app/1", "ws-fallback"]
});
await wt.ready;
console.log(wt.protocol);  // "my-app/1" — whatever the server picked