Cloudflare Agents SDK

Status: Production Ready ✅ Last Updated: 2025-10-21 Dependencies: cloudflare-worker-base (recommended) Latest Versions: agents@latest, @modelcontextprotocol/sdk@latest Production Tested: Cloudflare's own MCP servers (https://github.com/cloudflare/mcp-server-cloudflare)

What is Cloudflare Agents?

The Cloudflare Agents SDK enables building AI-powered autonomous agents that run on Cloudflare Workers + Durable Objects. Agents can:

• Communicate in real-time via WebSockets and Server-Sent Events
• Persist state with built-in SQLite database (up to 1GB per agent)
• Schedule tasks using delays, specific dates, or cron expressions
• Run workflows by triggering asynchronous Cloudflare Workflows
• Browse the web using Browser Rendering API + Puppeteer
• Implement RAG with Vectorize vector database + Workers AI embeddings
• Build MCP servers implementing the Model Context Protocol
• Support human-in-the-loop patterns for review and approval
• Scale to millions of independent agent instances globally

Each agent instance is a globally unique, stateful micro-server that can run for seconds, minutes, or hours.

Quick Start (10 Minutes)

1. Scaffold Project with Template

npm create cloudflare@latest my-agent -- \
  --template=cloudflare/agents-starter \
  --ts \
  --git \
  --deploy false

What this creates:

• Complete Agent project structure
• TypeScript configuration
• wrangler.jsonc with Durable Objects bindings
• Example chat agent implementation
• React client with useAgent hook

2. Or Add to Existing Worker

cd my-existing-worker
npm install agents

Then create an Agent class:

// src/index.ts
import { Agent, AgentNamespace } from "agents";

export class MyAgent extends Agent {
  async onRequest(request: Request): Promise<Response> {
    return new Response("Hello from Agent!");
  }
}

export default MyAgent;

3. Configure Durable Objects Binding

Create or update wrangler.jsonc:

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "my-agent",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-21",
  "compatibility_flags": ["nodejs_compat"],
  "durable_objects": {
    "bindings": [
      {
        "name": "MyAgent",        // MUST match class name
        "class_name": "MyAgent"   // MUST match exported class
      }
    ]
  },
  "migrations": [
    {
      "tag": "v1",
      "new_sqlite_classes": ["MyAgent"]  // CRITICAL: Enables SQLite storage
    }
  ]
}

CRITICAL Configuration Rules:

• ✅ name and class_name MUST be identical
• ✅ new_sqlite_classes MUST be in first migration (cannot add later)
• ✅ Agent class MUST be exported (or binding will fail)
• ✅ Migration tags CANNOT be reused (each migration needs unique tag)

4. Deploy

npx wrangler@latest deploy

Your agent is now running at: https://my-agent.<subdomain>.workers.dev

Configuration Deep Dive

Complete wrangler.jsonc Example

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "my-agent",
  "main": "src/index.ts",
  "account_id": "YOUR_ACCOUNT_ID",
  "compatibility_date": "2025-10-21",
  "compatibility_flags": ["nodejs_compat"],

  // Durable Objects configuration (REQUIRED)
  "durable_objects": {
    "bindings": [
      {
        "name": "MyAgent",
        "class_name": "MyAgent"
      }
    ]
  },

  // Migrations (REQUIRED)
  "migrations": [
    {
      "tag": "v1",
      "new_sqlite_classes": ["MyAgent"]  // Enables state persistence
    }
  ],

  // Optional: Workers AI binding (for AI model calls)
  "ai": {
    "binding": "AI"
  },

  // Optional: Vectorize binding (for RAG)
  "vectorize": {
    "bindings": [
      {
        "binding": "VECTORIZE",
        "index_name": "my-agent-vectors"
      }
    ]
  },

  // Optional: Browser Rendering binding (for web browsing)
  "browser": {
    "binding": "BROWSER"
  },

  // Optional: Workflows binding (for async workflows)
  "workflows": [
    {
      "name": "MY_WORKFLOW",
      "class_name": "MyWorkflow",
      "script_name": "my-workflow-script"  // If in different project
    }
  ],

  // Optional: D1 binding (for additional persistent data)
  "d1_databases": [
    {
      "binding": "DB",
      "database_name": "my-agent-db",
      "database_id": "your-database-id"
    }
  ],

  // Optional: R2 binding (for file storage)
  "r2_buckets": [
    {
      "binding": "BUCKET",
      "bucket_name": "my-agent-files"
    }
  ],

  // Optional: Environment variables
  "vars": {
    "ENVIRONMENT": "production"
  },

  // Optional: Secrets (set with: wrangler secret put KEY)
  // OPENAI_API_KEY, ANTHROPIC_API_KEY, etc.

  // Observability
  "observability": {
    "enabled": true
  }
}

Migrations Best Practices

Atomic Deployments: Migrations are atomic operations - they cannot be gradually deployed.

{
  "migrations": [
    {
      "tag": "v1",
      "new_sqlite_classes": ["MyAgent"]  // Initial: enable SQLite
    },
    {
      "tag": "v2",
      "renamed_classes": [
        {"from": "MyAgent", "to": "MyRenamedAgent"}
      ]
    },
    {
      "tag": "v3",
      "deleted_classes": ["OldAgent"]
    },
    {
      "tag": "v4",
      "transferred_classes": [
        {
          "from": "AgentInOldScript",
          "from_script": "old-worker",
          "to": "AgentInNewScript"
        }
      ]
    }
  ]
}

Migration Rules:

• ✅ Each migration needs a unique tag
• ✅ Cannot enable SQLite on existing deployed class (must be in first migration)
• ✅ Migrations apply in order during deployment
• ✅ Cannot edit or remove previous migration tags
• ❌ Never deploy new migrations gradually (atomic only)

Environment-Specific Migrations

{
  "migrations": [{"tag": "v1", "new_sqlite_classes": ["MyAgent"]}],
  "env": {
    "staging": {
      "migrations": [
        {"tag": "v1", "new_sqlite_classes": ["MyAgent"]},
        {"tag": "v2-staging", "renamed_classes": [{"from": "MyAgent", "to": "StagingAgent"}]}
      ]
    }
  }
}

Agent Class API

The Agent class is the foundation of the Agents SDK. Extend it to create your agent.

Basic Agent Structure

import { Agent } from "agents";

interface Env {
  // Environment variables and bindings
  OPENAI_API_KEY: string;
  AI: Ai;
  VECTORIZE: Vectorize;
  DB: D1Database;
}

interface State {
  // Your agent's persistent state
  counter: number;
  messages: string[];
  lastUpdated: Date | null;
}

export class MyAgent extends Agent<Env, State> {
  // Optional: Set initial state (first time agent is created)
  initialState: State = {
    counter: 0,
    messages: [],
    lastUpdated: null
  };

  // Optional: Called when agent instance starts or wakes from hibernation
  async onStart() {
    console.log('Agent started:', this.name, 'State:', this.state);
  }

  // Handle HTTP requests
  async onRequest(request: Request): Promise<Response> {
    return Response.json({ message: "Hello from Agent", state: this.state });
  }

  // Handle WebSocket connections (optional)
  async onConnect(connection: Connection, ctx: ConnectionContext) {
    console.log('Client connected:', connection.id);
    // Connections are automatically accepted
  }

  // Handle WebSocket messages (optional)
  async onMessage(connection: Connection, message: WSMessage) {
    if (typeof message === 'string') {
      connection.send(`Echo: ${message}`);
    }
  }

  // Handle WebSocket errors (optional)
  async onError(connection: Connection, error: unknown): Promise<void> {
    console.error('Connection error:', error);
  }

  // Handle WebSocket close (optional)
  async onClose(connection: Connection, code: number, reason: string, wasClean: boolean): Promise<void> {
    console.log('Connection closed:', code, reason);
  }

  // Called when state is updated from any source (optional)
  onStateUpdat