# WebSocket API
WebSocket API allows your Function to act as a full WebSocket server or client and proxy bidirectional traffic to backend services. This unlocks real-time use cases such as chat, multiplayer games, telemetry dashboards, and AI inference streams—all served directly from the edge for sub-second latency.
:::note
At the moment, this capability is exclusively accessible to customers with **Business**, **Enterprise**, and **Mission-Critical** Support, also available in the **Reserved Capacity** or **Saving Plan** contracts. [Contact the Support team](https://tickets.azion.com/en/support/loginen/support/login/new) to request access to this capability.
:::
## Server and Client Modes
- Use the `upgradeWebSocket()` function to handle server-side WebSocket upgrade requests.
- For client-side, outbound connections, use the standard `WebSocket(url)` API.
## Broadcast Helpers
- Easily broadcast messages to all connected clients using built-in helpers, enabling efficient fan-out with minimal code.
## Metrics and Logs
These events are visible in Real-Time Metrics and LogStream, helping you monitor connection and message activities.
- `websocket.connection.accepted`
- `message.sent`
- `message.received`
## Firewall Support
- Firewall rules can inspect WebSocket traffic before the upgrade process is finalized.
- Ensure your firewall policies are configured to handle WebSocket connections as needed.
## Example
```javascript
export default {
async fetch(request, env, ctx) {
// Check if the request is a WebSocket upgrade
if (request.headers.get("upgrade") === "websocket") {
// Use the upgradeWebSocket function to handle the WebSocket upgrade
const { response, socket } = upgradeWebSocket(request);
// Handle WebSocket events
socket.addEventListener("open", () => {
console.log("WebSocket connection established");
});
socket.addEventListener("message", (event) => {
console.log(`Message received: ${event.data}`);
socket.send("pong"); // Respond with "pong"
});
socket.addEventListener("close", () => {
console.log("WebSocket connection closed");
});
socket.addEventListener("error", (error) => {
console.error("WebSocket error:", error);
});
// Return the response to complete the WebSocket upgrade
return response;
}
// If the request is not a WebSocket upgrade, serve a simple HTML page
const htmlContent = `
WebSocket Example
WebSocket Example
`;
return new Response(htmlContent, {
status: 200,
headers: { "Content-Type": "text/html" },
});
},
};
```