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484 lines (345 loc) · 10.5 KB
title Add to existing project
pcx_content_type how-to
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import { PackageManagers, TypeScriptExample, WranglerConfig, LinkCard, } from "~/components";

This guide shows how to add agents to an existing Cloudflare Workers project. If you are starting fresh, refer to Building a chat agent instead.

Prerequisites

  • An existing Cloudflare Workers project with a Wrangler configuration file
  • Node.js 18 or newer

1. Install the package

For React applications, no additional packages are needed — React bindings are included.

For Hono applications:

2. Create an Agent

Create a new file for your agent (for example, src/agents/counter.ts):

import { Agent, callable } from "agents";

export type CounterState = {
	count: number;
};

export class CounterAgent extends Agent<Env, CounterState> {
	initialState: CounterState = { count: 0 };

	@callable()
	increment() {
		this.setState({ count: this.state.count + 1 });
		return this.state.count;
	}

	@callable()
	decrement() {
		this.setState({ count: this.state.count - 1 });
		return this.state.count;
	}
}

3. Update Wrangler configuration

Add the Durable Object binding and migration:

{
	"name": "my-existing-project",
	"main": "src/index.ts",
	"compatibility_date": "$today",
	"compatibility_flags": ["nodejs_compat"],

	"durable_objects": {
		"bindings": [
			{
				"name": "CounterAgent",
				"class_name": "CounterAgent",
			},
		],
	},

	"migrations": [
		{
			"tag": "v1",
			"new_sqlite_classes": ["CounterAgent"],
		},
	],
}

Key points:

  • name in bindings becomes the property on env (for example, env.CounterAgent)
  • class_name must exactly match your exported class name
  • new_sqlite_classes enables SQLite storage for state persistence
  • nodejs_compat flag is required for the agents package

4. Export the Agent class

Your agent class must be exported from your main entry point. Update your src/index.ts:

// Export the agent class (required for Durable Objects)
export { CounterAgent } from "./agents/counter";

// Your existing exports...
export default {
	// ...
} satisfies ExportedHandler<Env>;

5. Wire up routing

Choose the approach that matches your project structure:

Plain Workers (fetch handler)

import { routeAgentRequest } from "agents";
export { CounterAgent } from "./agents/counter";

export default {
	async fetch(request: Request, env: Env, ctx: ExecutionContext) {
		// Try agent routing first
		const agentResponse = await routeAgentRequest(request, env);
		if (agentResponse) return agentResponse;

		// Your existing routing logic
		const url = new URL(request.url);
		if (url.pathname === "/api/hello") {
			return Response.json({ message: "Hello!" });
		}

		return new Response("Not found", { status: 404 });
	},
} satisfies ExportedHandler<Env>;

Hono

import { Hono } from "hono";
import { agentsMiddleware } from "hono-agents";
export { CounterAgent } from "./agents/counter";

const app = new Hono<{ Bindings: Env }>();

// Add agents middleware - handles WebSocket upgrades and agent HTTP requests
app.use("*", agentsMiddleware());

// Your existing routes continue to work
app.get("/api/hello", (c) => c.json({ message: "Hello!" }));

export default app;

With static assets

If you are serving static assets alongside agents, static assets are served first by default. Your Worker code only runs for paths that do not match a static asset:

import { routeAgentRequest } from "agents";
export { CounterAgent } from "./agents/counter";

export default {
	async fetch(request: Request, env: Env, ctx: ExecutionContext) {
		// Static assets are served automatically before this runs
		// This only handles non-asset requests

		// Route to agents
		const agentResponse = await routeAgentRequest(request, env);
		if (agentResponse) return agentResponse;

		return new Response("Not found", { status: 404 });
	},
} satisfies ExportedHandler<Env>;

Configure assets in the Wrangler configuration file:

{
	"assets": {
		"directory": "./public",
	},
}

6. Generate TypeScript types

Do not hand-write your Env interface. Run wrangler types to generate a type definition file that matches your Wrangler configuration. This catches mismatches between your config and code at compile time instead of at deploy time.

Re-run wrangler types whenever you add or rename a binding.

npx wrangler types

This creates a type definition file with all your bindings typed, including your agent Durable Object namespaces. The Agent class defaults to using the generated Env type, so you do not need to pass it as a type parameter — extends Agent is sufficient unless you need to pass a second type parameter for state (for example, Agent<Env, CounterState>).

Refer to Configuration for more details on type generation.

7. Connect from the frontend

React

import { useState } from "react";
import { useAgent } from "agents/react";
import type { CounterAgent, CounterState } from "./agents/counter";

function CounterWidget() {
	const [count, setCount] = useState(0);

	const agent = useAgent<CounterAgent, CounterState>({
		agent: "CounterAgent",
		onStateUpdate: (state) => setCount(state.count),
	});

	return (
		<>
			{count}
			<button onClick={() => agent.stub.increment()}>+</button>
			<button onClick={() => agent.stub.decrement()}>-</button>
		</>
	);
}

Vanilla JavaScript

import { AgentClient } from "agents/client";

const agent = new AgentClient({
	agent: "CounterAgent",
	name: "user-123", // Optional: unique instance name
	onStateUpdate: (state) => {
		document.getElementById("count").textContent = state.count;
	},
});

// Call methods
document.getElementById("increment").onclick = () => agent.call("increment");

Adding multiple agents

Add more agents by extending the configuration:

// src/agents/chat.ts
export class Chat extends Agent {
	// ...
}

// src/agents/scheduler.ts
export class Scheduler extends Agent {
	// ...
}

Update the Wrangler configuration file:

{
	"durable_objects": {
		"bindings": [
			{ "name": "CounterAgent", "class_name": "CounterAgent" },
			{ "name": "Chat", "class_name": "Chat" },
			{ "name": "Scheduler", "class_name": "Scheduler" },
		],
	},
	"migrations": [
		{
			"tag": "v1",
			"new_sqlite_classes": ["CounterAgent", "Chat", "Scheduler"],
		},
	],
}

Export all agents from your entry point:

export { CounterAgent } from "./agents/counter";
export { Chat } from "./agents/chat";
export { Scheduler } from "./agents/scheduler";

Common integration patterns

Agents behind authentication

Check auth before routing to agents:

export default {
	async fetch(request: Request, env: Env) {
		// Check auth for agent routes
		if (request.url.includes("/agents/")) {
			const authResult = await checkAuth(request, env);
			if (!authResult.valid) {
				return new Response("Unauthorized", { status: 401 });
			}
		}

		const agentResponse = await routeAgentRequest(request, env);
		if (agentResponse) return agentResponse;

		// ... rest of routing
	},
} satisfies ExportedHandler<Env>;

Custom agent path prefix

By default, agents are routed at /agents/{agent-name}/{instance-name}. You can customize this:

import { routeAgentRequest } from "agents";

const agentResponse = await routeAgentRequest(request, env, {
	prefix: "/api/agents", // Now routes at /api/agents/{agent-name}/{instance-name}
});

Refer to Routing for more options including CORS, custom instance naming, and location hints.

Accessing agents from server code

You can interact with agents directly from your Worker code:

import { getAgentByName } from "agents";

export default {
	async fetch(request: Request, env: Env) {
		if (request.url.endsWith("/api/increment")) {
			// Get a specific agent instance
			const counter = await getAgentByName(env.CounterAgent, "shared-counter");
			const newCount = await counter.increment();
			return Response.json({ count: newCount });
		}
		// ...
	},
} satisfies ExportedHandler<Env>;

Troubleshooting

Agent not found, or 404 errors

  1. Check the export - Agent class must be exported from your main entry point.
  2. Check the binding - class_name in the Wrangler configuration file must exactly match the exported class name.
  3. Check the route - Default route is /agents/{agent-name}/{instance-name}.

No such Durable Object class error

Add the migration to the Wrangler configuration file:

{
	"migrations": [
		{
			"tag": "v1",
			"new_sqlite_classes": ["YourAgentClass"],
		},
	],
}

WebSocket connection fails

Ensure your routing passes the response unchanged:

// Correct - return the response directly
const agentResponse = await routeAgentRequest(request, env);
if (agentResponse) return agentResponse;

// Wrong - this breaks WebSocket connections
if (agentResponse) return new Response(agentResponse.body);

State not persisting

Check that:

  1. You are using this.setState(), not mutating this.state directly.
  2. The agent class is in new_sqlite_classes in migrations.
  3. You are connecting to the same agent instance name.

Next steps