Readonly connections

Readonly connections restrict certain WebSocket clients from modifying agent state while still letting them receive state updates and call non-mutating RPC methods.

Overview

When a connection is marked as readonly:

It receives state updates from the server
It can call RPC methods that do not modify state
It cannot call this.setState() — neither via client-side setState() nor via a @callable() method that calls this.setState() internally

This is useful for scenarios like:

View-only modes: Users who should only observe but not modify
Role-based access: Restricting state modifications based on user roles
Multi-tenant scenarios: Some tenants have read-only access
Audit and monitoring connections: Observers that should not affect the system

import { Agent } from "agents";

export class DocAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		return url.searchParams.get("mode") === "view";
	}
}

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

export class DocAgent extends Agent<Env, DocState> {
	shouldConnectionBeReadonly(connection: Connection, ctx: ConnectionContext) {
		const url = new URL(ctx.request.url);
		return url.searchParams.get("mode") === "view";
	}
}

// Client - view-only mode
const agent = useAgent({
	agent: "DocAgent",
	name: "doc-123",
	query: { mode: "view" },
	onStateUpdateError: (error) => {
		toast.error("You're in view-only mode");
	},
});

// Client - view-only mode
const agent = useAgent({
	agent: "DocAgent",
	name: "doc-123",
	query: { mode: "view" },
	onStateUpdateError: (error) => {
		toast.error("You're in view-only mode");
	},
});

Marking connections as readonly

On connect

Override shouldConnectionBeReadonly to evaluate each connection when it first connects. Return true to mark it readonly.

export class MyAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		const role = url.searchParams.get("role");
		return role === "viewer" || role === "guest";
	}
}

export class MyAgent extends Agent<Env, State> {
	shouldConnectionBeReadonly(
		connection: Connection,
		ctx: ConnectionContext,
	): boolean {
		const url = new URL(ctx.request.url);
		const role = url.searchParams.get("role");
		return role === "viewer" || role === "guest";
	}
}

This hook runs before the initial state is sent to the client, so the connection is readonly from the very first message.

At any time

Use setConnectionReadonly to change a connection's readonly status dynamically:

export class GameAgent extends Agent {
	@callable()
	async startSpectating() {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, true);
		}
	}

	@callable()
	async joinAsPlayer() {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, false);
		}
	}
}

export class GameAgent extends Agent<Env, GameState> {
	@callable()
	async startSpectating() {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, true);
		}
	}

	@callable()
	async joinAsPlayer() {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, false);
		}
	}
}

Letting a connection toggle its own status

A connection can toggle its own readonly status via a callable. This is useful for lock/unlock UIs where viewers can opt into editing mode:

import { Agent, callable, getCurrentAgent } from "agents";

export class CollabAgent extends Agent {
	@callable()
	async setMyReadonly(readonly) {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, readonly);
		}
	}
}

import { Agent, callable, getCurrentAgent } from "agents";

export class CollabAgent extends Agent<Env, State> {
	@callable()
	async setMyReadonly(readonly: boolean) {
		const { connection } = getCurrentAgent();
		if (connection) {
			this.setConnectionReadonly(connection, readonly);
		}
	}
}

On the client:

// Toggle between readonly and writable
await agent.call("setMyReadonly", [true]); // lock
await agent.call("setMyReadonly", [false]); // unlock

// Toggle between readonly and writable
await agent.call("setMyReadonly", [true]); // lock
await agent.call("setMyReadonly", [false]); // unlock

Checking status

Use isConnectionReadonly to check a connection's current status:

export class MyAgent extends Agent {
	@callable()
	async getPermissions() {
		const { connection } = getCurrentAgent();
		if (connection) {
			return { canEdit: !this.isConnectionReadonly(connection) };
		}
	}
}

export class MyAgent extends Agent<Env, State> {
	@callable()
	async getPermissions() {
		const { connection } = getCurrentAgent();
		if (connection) {
			return { canEdit: !this.isConnectionReadonly(connection) };
		}
	}
}

Handling errors on the client

Errors surface in two ways depending on how the write was attempted:

Client-side setState() — the server sends a cf_agent_state_error message. Handle it with the onStateUpdateError callback.
@callable() methods — the RPC call rejects with an error. Handle it with a try/catch around agent.call().

const agent = useAgent({
	agent: "MyAgent",
	name: "instance",
	// Fires when client-side setState() is blocked
	onStateUpdateError: (error) => {
		setError(error);
	},
});

// Fires when a callable that writes state is blocked
try {
	await agent.call("updateSettings", [newSettings]);
} catch (e) {
	setError(e instanceof Error ? e.message : String(e)); // "Connection is readonly"
}

const agent = useAgent({
	agent: "MyAgent",
	name: "instance",
	// Fires when client-side setState() is blocked
	onStateUpdateError: (error) => {
		setError(error);
	},
});

// Fires when a callable that writes state is blocked
try {
	await agent.call("updateSettings", [newSettings]);
} catch (e) {
	setError(e instanceof Error ? e.message : String(e)); // "Connection is readonly"
}

To avoid showing errors in the first place, check permissions before rendering edit controls:

function Editor() {
	const [canEdit, setCanEdit] = useState(false);
	const agent = useAgent({ agent: "MyAgent", name: "instance" });

	useEffect(() => {
		agent.call("getPermissions").then((p) => setCanEdit(p.canEdit));
	}, []);

	return <button disabled={!canEdit}>{canEdit ? "Edit" : "View Only"}</button>;
}

API reference

`shouldConnectionBeReadonly`

An overridable hook that determines if a connection should be marked as readonly when it connects.

Parameter	Type	Description
`connection`	`Connection`	The connecting client
`ctx`	`ConnectionContext`	Contains the upgrade request
Returns	`boolean`	`true` to mark as readonly

Default: returns false (all connections are writable).

`setConnectionReadonly`

Mark or unmark a connection as readonly. Can be called at any time.

Parameter	Type	Description
`connection`	`Connection`	The connection to update
`readonly`	`boolean`	`true` to make readonly (default: `true`)

`isConnectionReadonly`

Check if a connection is currently readonly.

Parameter	Type	Description
`connection`	`Connection`	The connection to check
Returns	`boolean`	`true` if readonly

`onStateUpdateError` (client)

Callback on AgentClient and useAgent options. Called when the server rejects a state update.

Parameter	Type	Description
`error`	`string`	Error message from the server

Examples

Query parameter based access

export class DocumentAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		const mode = url.searchParams.get("mode");
		return mode === "view";
	}
}

// Client connects with readonly mode
const agent = useAgent({
	agent: "DocumentAgent",
	name: "doc-123",
	query: { mode: "view" },
	onStateUpdateError: (error) => {
		toast.error("Document is in view-only mode");
	},
});

export class DocumentAgent extends Agent<Env, DocumentState> {
	shouldConnectionBeReadonly(
		connection: Connection,
		ctx: ConnectionContext,
	): boolean {
		const url = new URL(ctx.request.url);
		const mode = url.searchParams.get("mode");
		return mode === "view";
	}
}

// Client connects with readonly mode
const agent = useAgent({
	agent: "DocumentAgent",
	name: "doc-123",
	query: { mode: "view" },
	onStateUpdateError: (error) => {
		toast.error("Document is in view-only mode");
	},
});

Role-based access control

export class CollaborativeAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		const role = url.searchParams.get("role");
		return role === "viewer" || role === "guest";
	}

	onConnect(connection, ctx) {
		const url = new URL(ctx.request.url);
		const userId = url.searchParams.get("userId");

		console.log(
			`User ${userId} connected (readonly: ${this.isConnectionReadonly(connection)})`,
		);
	}

	@callable()
	async upgradeToEditor() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		// Check permissions (pseudo-code)
		const canUpgrade = await checkUserPermissions();
		if (canUpgrade) {
			this.setConnectionReadonly(connection, false);
			return { success: true };
		}

		throw new Error("Insufficient permissions");
	}
}

export class CollaborativeAgent extends Agent<Env, CollabState> {
	shouldConnectionBeReadonly(
		connection: Connection,
		ctx: ConnectionContext,
	): boolean {
		const url = new URL(ctx.request.url);
		const role = url.searchParams.get("role");
		return role === "viewer" || role === "guest";
	}

	onConnect(connection: Connection, ctx: ConnectionContext) {
		const url = new URL(ctx.request.url);
		const userId = url.searchParams.get("userId");

		console.log(
			`User ${userId} connected (readonly: ${this.isConnectionReadonly(connection)})`,
		);
	}

	@callable()
	async upgradeToEditor() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		// Check permissions (pseudo-code)
		const canUpgrade = await checkUserPermissions();
		if (canUpgrade) {
			this.setConnectionReadonly(connection, false);
			return { success: true };
		}

		throw new Error("Insufficient permissions");
	}
}

Admin dashboard

export class MonitoringAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		// Only admins can modify state
		return url.searchParams.get("admin") !== "true";
	}

	onStateChanged(state, source) {
		if (source !== "server") {
			// Log who modified the state
			console.log(`State modified by connection ${source.id}`);
		}
	}
}

// Admin client (can modify)
const adminAgent = useAgent({
	agent: "MonitoringAgent",
	name: "system",
	query: { admin: "true" },
});

// Viewer client (readonly)
const viewerAgent = useAgent({
	agent: "MonitoringAgent",
	name: "system",
	query: { admin: "false" },
	onStateUpdateError: (error) => {
		console.log("Viewer cannot modify state");
	},
});

export class MonitoringAgent extends Agent<Env, SystemState> {
	shouldConnectionBeReadonly(
		connection: Connection,
		ctx: ConnectionContext,
	): boolean {
		const url = new URL(ctx.request.url);
		// Only admins can modify state
		return url.searchParams.get("admin") !== "true";
	}

	onStateChanged(state: SystemState, source: Connection | "server") {
		if (source !== "server") {
			// Log who modified the state
			console.log(`State modified by connection ${source.id}`);
		}
	}
}

// Admin client (can modify)
const adminAgent = useAgent({
	agent: "MonitoringAgent",
	name: "system",
	query: { admin: "true" },
});

// Viewer client (readonly)
const viewerAgent = useAgent({
	agent: "MonitoringAgent",
	name: "system",
	query: { admin: "false" },
	onStateUpdateError: (error) => {
		console.log("Viewer cannot modify state");
	},
});

Dynamic permission changes

export class GameAgent extends Agent {
	@callable()
	async startSpectatorMode() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		this.setConnectionReadonly(connection, true);
		return { mode: "spectator" };
	}

	@callable()
	async joinAsPlayer() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		const canJoin = this.state.players.length < 4;
		if (canJoin) {
			this.setConnectionReadonly(connection, false);
			return { mode: "player" };
		}

		throw new Error("Game is full");
	}

	@callable()
	async getMyPermissions() {
		const { connection } = getCurrentAgent();
		if (!connection) return null;

		return {
			canEdit: !this.isConnectionReadonly(connection),
			connectionId: connection.id,
		};
	}
}

export class GameAgent extends Agent<Env, GameState> {
	@callable()
	async startSpectatorMode() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		this.setConnectionReadonly(connection, true);
		return { mode: "spectator" };
	}

	@callable()
	async joinAsPlayer() {
		const { connection } = getCurrentAgent();
		if (!connection) return;

		const canJoin = this.state.players.length < 4;
		if (canJoin) {
			this.setConnectionReadonly(connection, false);
			return { mode: "player" };
		}

		throw new Error("Game is full");
	}

	@callable()
	async getMyPermissions() {
		const { connection } = getCurrentAgent();
		if (!connection) return null;

		return {
			canEdit: !this.isConnectionReadonly(connection),
			connectionId: connection.id,
		};
	}
}

Client-side React component:

function GameComponent() {
	const [canEdit, setCanEdit] = useState(false);

	const agent = useAgent({
		agent: "GameAgent",
		name: "game-123",
		onStateUpdateError: (error) => {
			toast.error("Cannot modify game state in spectator mode");
		},
	});

	useEffect(() => {
		agent.call("getMyPermissions").then((perms) => {
			setCanEdit(perms?.canEdit ?? false);
		});
	}, [agent]);

	return (
		<div>
			<button onClick={() => agent.call("joinAsPlayer")} disabled={canEdit}>
				Join as Player
			</button>

			<button
				onClick={() => agent.call("startSpectatorMode")}
				disabled={!canEdit}
			>
				Switch to Spectator
			</button>

			<div>{canEdit ? "You can modify the game" : "You are spectating"}</div>
		</div>
	);
}

How it works

Readonly status is stored in the connection's WebSocket attachment, which persists through the WebSocket Hibernation API. The flag is namespaced internally so it cannot be accidentally overwritten by connection.setState(). The same mechanism is used by protocol message control — both flag coexist safely in the attachment. This means:

Survives hibernation — the flag is serialized and restored when the agent wakes up
No cleanup needed — connection state is automatically discarded when the connection closes
Zero overhead — no database tables or queries, just the connection's built-in attachment
Safe from user code — connection.state and connection.setState() never expose or overwrite the readonly flag

When a readonly connection tries to modify state, the server blocks it — regardless of whether the write comes from client-side setState() or from a @callable() method:

Client (readonly)                     Agent
       │                                │
       │  setState({ count: 1 })        │
       │ ─────────────────────────────▶ │  Check readonly → blocked
       │  ◀───────────────────────────  │
       │  cf_agent_state_error          │
       │                                │
       │  call("increment")             │
       │ ─────────────────────────────▶ │  increment() calls this.setState()
       │                                │  Check readonly → throw
       │  ◀───────────────────────────  │
       │  RPC error: "Connection is     │
       │              readonly"         │
       │                                │
       │  call("getPermissions")        │
       │ ─────────────────────────────▶ │  getPermissions() — no setState()
       │  ◀───────────────────────────  │
       │  RPC result: { canEdit: false }│

What readonly does and does not restrict

Action	Allowed?
Receive state broadcasts	Yes
Call `@callable()` methods that do not write state	Yes
Call `@callable()` methods that call `this.setState()`	No
Send state updates via client-side `setState()`	No

The enforcement happens inside setState() itself. When a @callable() method tries to call this.setState() and the current connection context is readonly, the framework throws an Error("Connection is readonly"). This means you do not need manual permission checks in your RPC methods — any callable that writes state is automatically blocked for readonly connections.

Caveats

Side effects in callables still run

The readonly check happens inside this.setState(), not at the start of the callable. If your method has side effects before the state write, those will still execute:

export class MyAgent extends Agent {
	@callable()
	async processOrder(orderId) {
		await sendConfirmationEmail(orderId); // runs even for readonly connections
		await chargePayment(orderId); // runs too
		this.setState({ ...this.state, orders: [...this.state.orders, orderId] }); // throws
	}
}

export class MyAgent extends Agent<Env, State> {
	@callable()
	async processOrder(orderId: string) {
		await sendConfirmationEmail(orderId); // runs even for readonly connections
		await chargePayment(orderId); // runs too
		this.setState({ ...this.state, orders: [...this.state.orders, orderId] }); // throws
	}
}

To avoid this, either check permissions before side effects or structure your code so the state write comes first:

export class MyAgent extends Agent {
	@callable()
	async processOrder(orderId) {
		// Write state first — throws immediately for readonly connections
		this.setState({ ...this.state, orders: [...this.state.orders, orderId] });
		// Side effects only run if setState succeeded
		await sendConfirmationEmail(orderId);
		await chargePayment(orderId);
	}
}

export class MyAgent extends Agent<Env, State> {
	@callable()
	async processOrder(orderId: string) {
		// Write state first — throws immediately for readonly connections
		this.setState({ ...this.state, orders: [...this.state.orders, orderId] });
		// Side effects only run if setState succeeded
		await sendConfirmationEmail(orderId);
		await chargePayment(orderId);
	}
}

Best practices

Combine with authentication

export class SecureAgent extends Agent {
	shouldConnectionBeReadonly(connection, ctx) {
		const url = new URL(ctx.request.url);
		const token = url.searchParams.get("token");

		// Verify token and get permissions
		const permissions = this.verifyToken(token);
		return !permissions.canWrite;
	}
}

export class SecureAgent extends Agent<Env, State> {
	shouldConnectionBeReadonly(
		connection: Connection,
		ctx: ConnectionContext,
	): boolean {
		const url = new URL(ctx.request.url);
		const token = url.searchParams.get("token");

		// Verify token and get permissions
		const permissions = this.verifyToken(token);
		return !permissions.canWrite;
	}
}

Provide clear user feedback

const agent = useAgent({
	agent: "MyAgent",
	name: "instance",
	onStateUpdateError: (error) => {
		// User-friendly messages
		if (error.includes("readonly")) {
			showToast("You are in view-only mode. Upgrade to edit.");
		}
	},
});

const agent = useAgent({
	agent: "MyAgent",
	name: "instance",
	onStateUpdateError: (error) => {
		// User-friendly messages
		if (error.includes("readonly")) {
			showToast("You are in view-only mode. Upgrade to edit.");
		}
	},
});

Check permissions before UI actions

function EditButton() {
	const [canEdit, setCanEdit] = useState(false);
	const agent = useAgent({
		/* ... */
	});

	useEffect(() => {
		agent.call("checkPermissions").then((perms) => {
			setCanEdit(perms.canEdit);
		});
	}, []);

	return <button disabled={!canEdit}>{canEdit ? "Edit" : "View Only"}</button>;
}

Log access attempts

export class AuditedAgent extends Agent {
	onStateChanged(state, source) {
		if (source !== "server") {
			this.audit({
				action: "state_update",
				connectionId: source.id,
				readonly: this.isConnectionReadonly(source),
				timestamp: Date.now(),
			});
		}
	}
}

export class AuditedAgent extends Agent<Env, State> {
	onStateChanged(state: State, source: Connection | "server") {
		if (source !== "server") {
			this.audit({
				action: "state_update",
				connectionId: source.id,
				readonly: this.isConnectionReadonly(source),
				timestamp: Date.now(),
			});
		}
	}
}

Limitations

Readonly status only applies to state updates using setState()
RPC methods can still be called (implement your own checks if needed)
Readonly is a per-connection flag, not tied to user identity

Store and sync state
Protocol messages — suppress JSON protocol frames for binary-only clients (can be combined with readonly)
WebSockets
Callable methods