---
description: Turn off the identity, state, and MCP protocol frames an Agent sends to WebSocket clients, for binary or minimal clients.
title: Protocol messages
image: https://developers.cloudflare.com/agents/agent-class/protocol-messages/og.png?v=c964d35f5aa8e9cf
---

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# Protocol messages

Last updated Oct 29, 2026|Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/agents/agent-class/protocol-messages/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

When a client connects, an Agent sends it JSON protocol frames: its identity (`cf_agent_identity`), its state (`cf_agent_state`), and its MCP servers (`cf_agent_mcp_servers`). It sends state and MCP frames again whenever they change. `useAgent` and `AgentClient` read these frames for you.

Some clients cannot handle JSON text frames, such as IoT devices or MQTT clients. Return `false` from `shouldSendProtocolMessages()` to turn the frames off for them:

```js
import { Agent } from "agents";

export class DeviceAgent extends Agent {
	shouldSendProtocolMessages(_connection, ctx) {
		return ctx.request.headers.get("Sec-WebSocket-Protocol") !== "mqtt";
	}
}
```

```ts
import { Agent, type Connection, type ConnectionContext } from "agents";

export class DeviceAgent extends Agent<Env> {
	shouldSendProtocolMessages(_connection: Connection, ctx: ConnectionContext) {
		return ctx.request.headers.get("Sec-WebSocket-Protocol") !== "mqtt";
	}
}
```

The decision is made once, when the connection is accepted, and survives hibernation. A connection without protocol frames still sends and receives your own messages, receives `this.broadcast()`, and can call `@callable()` methods. `isConnectionProtocolEnabled(connection)` returns the current setting.

This uses the `protocol` option of the `WebSockets` capability. For more information, refer to [Control the protocol per connection](https://developers.cloudflare.com/agents/runtime/capabilities/websockets/#control-the-protocol-per-connection).

### [Readonly connections](https://developers.cloudflare.com/agents/agent-class/readonly-connections/)

Let a connection receive state without changing it.

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