---
title: WebSocket
description: Serve your procedures over a WebSocket and keep one connection for every call.
---

Server via [crossws](https://github.com/h3js/crossws) (optional peer). Same `path` / `createContext` / `onError` as [HTTP](/tacho/transport/http). Streams are not supported - a stream procedure is `INTERNAL_ERROR`.

> **Security:** The WS handler does not authenticate connections by default. Use `createContext` to verify credentials on every message, or guard the upgrade path itself. An unauthenticated socket can call any procedure.

```ts twoslash
// @noErrors
import { handle } from "tacho/transport/ws";
import { serve } from "crossws/server";
import { tacho } from "tacho";

const rpc = tacho();
const router = rpc({ ping: rpc.run(() => "pong" as const) });
// ---cut---
serve({
  websocket: handle(router, {
    path: "/rpc",
    createContext: (peer) => ({
      user: String(peer.context["user"] ?? ""),
    }),
    onError: (err) => console.error(err),
  }),
});
```

Client from `tacho/client/ws`. One socket. `.ready` and `.close()`.

```ts twoslash
import { createClient } from "tacho/client/ws";
import { tacho } from "tacho";

const rpc = tacho();
const router = rpc({ ping: rpc.run(() => "pong" as const) });
type Router = typeof router;
// ---cut---
const ws = createClient<Router>({
  url: "ws://localhost:3000",
  protocols: "tacho",
});
await ws.ready;
await ws.ping();
ws.close();
```

| option       |                                         |
| ------------ | --------------------------------------- |
| `url`        | WebSocket URL.                          |
| `protocols`  | Passed to `WebSocket`.                  |
| `WebSocket`  | Custom constructor. Defaults to global. |
| `serializer` | Custom serializer.                      |