# Getting Started

> crossws provides a cross-platform toolkit to define well-typed WebSocket apps that can then be integrated into various WebSocket servers using built-in adapters.

Writing a realtime WebSocket server that can work in different runtimes is challenging because there is no single standard for WebSocket servers. You often need to go into many details of different API implementations and it also makes switching from one runtime costly. crossws is a solution to this!

## Quick Start

<tip>

You can try crossws with [online playground](https://stackblitz.com/github/h3js/crossws/tree/main/playground).

</tip>

Install `crossws` and `srvx` in your project:

<pm-install name="crossws srvx">



</pm-install>

A simple WebSocket server looks like this:

```js [server.mjs]
// Works with Bun, Deno and Node.js (also Cloudflare or SSE as fallback)
import { serve } from "crossws/server";

serve({
  websocket: {
    open(peer) {
      console.log("[ws] open", peer);
      peer.send({ user: "server", message: `Welcome ${peer}!` });
    },

    message(peer, message) {
      console.log("[ws] message", message);
      if (message.text().includes("ping")) {
        peer.send({ user: "server", message: "pong" });
      } else {
        peer.send({ user: peer.toString(), message: message.toString() });
      }
    },

    close(peer, event) {
      console.log("[ws] close", peer, event);
    },

    error(peer, error) {
      console.log("[ws] error", peer, error);
    },
  },
  fetch: () =>
    fetch(
      "https://raw.githubusercontent.com/h3js/crossws/refs/heads/main/playground/public/index.html",
    ).then((res) => new Response(res.body, { headers: { "Content-Type": "text/html" } })),
});
```

Then, run the server using your favorite runtime:

<code-group>

```bash [node]
node server.mjs
```

```bash [deno]
deno run --allow-env --allow-net server.mjs
```

```bash [bun]
bun run server.mjs
```

</code-group>

<alert>

When using `crossws/server`, export conditions automatically resolve the right runtime adapter and integrate with [💥 srvx](https://srvx.h3.dev). You can alternatively, manually integrate crossws with [Adapters](/adapters).

</alert>

<read-more title="Hooks" to="/guide/hooks">

See [Hooks](/guide/hooks) for more usage details.

</read-more>

<read-more title="Adapters" to="/adapters">

Hooks API is exactly same on all runtimes. See [Adapters](/adapters) for integration details.

</read-more>