Overview

Silt is the E2B of UDP — a sub-100ms, scale-to-zero platform for WebTransport / UDP workloads. Spin up a real-time room in under 100ms, pay nothing while it’s idle, and never touch the QUIC, cert, or routing plumbing.

A room gives every peer two lanes over one WebTransport connection:

• Presence — unreliable datagrams, latest-wins, the ~20Hz position firehose.
• Events — reliable, ordered, for discrete actions you can’t drop.

A plain WebSocket can’t do the unreliable lane — it head-of-line-blocks under loss. That two-lane split is what Silt is for.

import { joinRoom } from "@silt/client";

const room = await joinRoom("https://demo.silt.run/room/graveyard", { id: "alice" });

room.on("presence", (peerId, state) => {
  console.log(peerId, "is at", state);
});

room.presence.set({ x: 10, y: 20, heading: 90 });

Tip

That’s the whole “hello room” — joinRoom → presence.set → on("presence"). No server code: the default room is a pure relay.

Where to go next

QuickstartJoin a room and sync presence in under 5 lines.

The two-lane modelPresence vs events — which lane carries what, and why.

API referenceEvery method and event on the @silt/client surface.

Wire protocolThe two-lane frame format, identity, and reconnect.

Run your ownSelf-host the pure-relay room server.

Why it’s real

• WebTransport hit browser Baseline (March 2026) — the iOS blocker is gone.
• Scale-to-zero with wake-on-packet — a room VM that doesn’t exist until someone arrives, woken on the first inbound packet inside the QUIC handshake’s retransmit window; restore measured under 100ms.
• Runs on Firecracker microVMs; the netns-crossing dataplane is proven live.
• Reference app Drifter — two people fly ships in one shared room over real WebTransport, proven across two devices on the public internet.