Cloudflare Agents SDK Builder

Cloudflare Agents SDK

Your knowledge of the Agents SDK may be outdated. Prefer retrieval over pre-training for any Agents SDK task.

Retrieval Sources

Cloudflare docs: https://developers.cloudflare.com/agents/index.md

Topic	Docs URL	Use for
Getting started	Quick start	First agent, project setup
Adding to existing project	Add to existing project	Install into existing Workers app
Configuration	Configuration	wrangler.jsonc, bindings, assets, deployment
Agent class	Agents API	Agent lifecycle, patterns, pitfalls
State	Store and sync state	setState, validateStateChange, persistence
Routing	Routing	URL patterns, routeAgentRequest
Callable methods	Callable methods	@callable, RPC, streaming, timeouts
Scheduling	Schedule tasks	schedule(), scheduleEvery(), cron
Workflows	Run workflows	AgentWorkflow, durable multi-step tasks
HTTP/WebSockets	WebSockets	Lifecycle hooks, hibernation
Chat agents	Chat agents	AIChatAgent, streaming, tools, persistence
Client SDK	Client SDK	useAgent, AgentClient, state, RPC, HTTP
Client tools	Client tools	Client-side tools, autoContinueAfterToolResult
Server-driven messages	Autonomous responses	saveMessages, waitUntilStable, server-initiated turns
Resumable streaming	Chat agents	Stream recovery on disconnect
Email	Email	Email routing, secure reply resolver
MCP client	MCP client	Connecting to MCP servers
MCP server	MCP server	Building MCP servers with createMcpHandler
MCP transports	MCP transports	Streamable HTTP, SSE, RPC transport options
Securing MCP servers	Securing MCP	OAuth, proxy MCP, hardening
Human-in-the-loop	Human-in-the-loop	Workflow approvals, elicitation, timeout handling
Durable execution	Durable execution	runFiber(), stash(), surviving DO eviction
Queue	Queue	Built-in FIFO queue, queue()
Retries	Retries	this.retry(), backoff/jitter
Observability	Observability	Diagnostics-channel events
Push notifications	Push notifications	Web Push + VAPID from agents
Webhooks	Webhooks	Receiving external webhooks
Cross-domain auth	Cross-domain auth	WebSocket auth, tokens, CORS
Readonly connections	Readonly	shouldConnectionBeReadonly
Voice	Voice	Experimental STT/TTS, withVoice
Browse the web	Browser tools	Experimental CDP browser automation
Think	Think	Experimental higher-level chat agent class
Migrations	AI SDK v5, AI SDK v6	Upgrading @cloudflare/ai-chat

Capabilities

The Agents SDK provides:

• Persistent state — SQLite-backed, auto-synced to clients via setState
• Callable RPC — @callable() methods invoked over WebSocket
• Scheduling — One-time, recurring (scheduleEvery), and cron tasks
• Workflows — Durable multi-step background processing via AgentWorkflow
• Durable execution — runFiber() / stash() for work that survives DO eviction
• Queue — Built-in FIFO queue with retries via queue()
• Retries — this.retry() with exponential backoff and jitter
• MCP integration — Connect to MCP servers or build your own with createMcpHandler
• Email handling — Receive and reply to emails with secure routing
• Streaming chat — AIChatAgent with resumable streams, message persistence, tools
• Server-driven messages — saveMessages, waitUntilStable for proactive agent turns
• React hooks — useAgent, useAgentChat for client apps
• Observability — diagnostics_channel events for state, RPC, schedule, lifecycle
• Push notifications — Web Push + VAPID delivery from agents
• Webhooks — Receive and verify external webhooks
• Voice (experimental) — STT/TTS via @cloudflare/voice
• Browser tools (experimental) — CDP-powered browsing via agents/browser
• Think (experimental) — Higher-level chat agent via @cloudflare/think

FIRST: Verify Installation

npm ls agents  # Should show agents package

If not installed:

npm install agents

For chat agents:

npm install agents @cloudflare/ai-chat ai @ai-sdk/react

Wrangler Configuration

{
  "compatibility_flags": ["nodejs_compat"],
  "durable_objects": {
    "bindings": [{ "name": "MyAgent", "class_name": "MyAgent" }]
  },
  "migrations": [{ "tag": "v1", "new_sqlite_classes": ["MyAgent"] }]
}

Gotchas:

• Do NOT enable experimentalDecorators in tsconfig (breaks @callable)
• Never edit old migrations — always add new tags
• Each agent class needs its own DO binding + migration entry
• Add "ai": { "binding": "AI" } for Workers AI

Agent Class

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

type State = { count: number };

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

  validateStateChange(nextState: State, source: Connection | "server") {
    if (nextState.count < 0) throw new Error("Count cannot be negative");
  }

  onStateUpdate(state: State, source: Connection | "server") {
    console.log("State updated:", state);
  }

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

export default {
  fetch: (req, env) => routeAgentRequest(req, env) ?? new Response("Not found", { status: 404 })
};

Routing

Requests route to /agents/{agent-name}/{instance-name}:

Class	URL
Counter	/agents/counter/user-123
ChatRoom	/agents/chat-room/lobby

Client: useAgent({ agent: "Counter", name: "user-123" })

Custom routing: use getAgentByName(env.MyAgent, "instance-id") then agent.fetch(request).

Core APIs

Task	API
Read state	this.state.count
Write state	this.setState({ count: 1 })
SQL query	this.sql`SELECT * FROM users WHERE id = ${id}`
Schedule (delay)	await this.schedule(60, "task", payload)
Schedule (cron)	await this.schedule("0 * * * *", "task", payload)
Schedule (interval)	await this.scheduleEvery(30, "poll")
RPC method	@callable() myMethod() { ... }
Streaming RPC	@callable({ streaming: true }) stream(res) { ... }
Start workflow	await this.runWorkflow("ProcessingWorkflow", params)
Durable fiber	await this.runFiber("name", async (ctx) => { ... })
Enqueue work	this.queue("handler", payload)
Retry with backoff	await this.retry(fn, { maxAttempts: 5 })
Broadcast to clients	this.broadcast(message)
Get connections	this.getConnections(tag?)

React Client

Read client-sdk.md for client selection and current connection examples. For chat UI and tools, also read streaming-chat.md.

References

Core

• references/state-scheduling.md — State persistence, scheduling, SQL
• references/callable.md — RPC methods, streaming, timeouts
• references/routing.md — URL patterns, custom routing, getAgentByName
• references/configuration.md — Wrangler config, bindings, Vite setup

Chat & Streaming

• references/streaming-chat.md — AIChatAgent, resumable streams, tools
• references/client-sdk.md — useAgent, useAgentChat, AgentClient
• references/server-driven-messages.md — Trigger patterns, saveMessages
• references/human-in-the-loop.md — Approval flows, needsApproval

Background Processing

• references/workflows.md — Durable Workflows integration
• references/durable-execution.md — runFiber, stash, surviving eviction
• references/queue-retries.md — Built-in queue, retry with backoff

Integrations

• references/mcp.md — MCP client and server, transports, securing
• references/email.md — Email routing and handling
• references/webhooks-push.md — Webhooks, push notifications
• references/observability.md — Diagnostics-channel events

Experimental

• references/think.md — @cloudflare/think higher-level chat agent
• references/voice.md — @cloudflare/voice STT/TTS
• references/codemode.md — Code Mode for tool orchestration
• references/browse-the-web.md — CDP browser tools