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Overview

website/src/content/docs/actors/index.mdx

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import { faCloudflare, faNodeJs, faReact, faNextjs } from "@rivet-gg/icons";

Quickstart

<CardGroup cols={2}> <Card title="Node.js & Bun" href="/docs/actors/quickstart/backend" icon={faNodeJs} > Set up actors with Node.js, Bun, and web frameworks </Card> <Card title="React" href="/docs/actors/quickstart/react" icon={faReact}> Build real-time React applications with actors </Card> <Card title="Next.js" href="/docs/actors/quickstart/next-js" icon={faNextjs} > Build server-rendered Next.js experiences backed by actors </Card> <Card title="Cloudflare Workers" href="/docs/actors/quickstart/cloudflare-workers" icon={faCloudflare} > Deploy actors on Cloudflare Workers with zero infrastructure </Card> </CardGroup>

Features

  • Long-Lived, Stateful Compute: Each unit of compute is like a tiny server that remembers things between requests – no need to re-fetch data from a database or worry about timeouts. Like AWS Lambda, but with memory and no timeouts.
  • Blazing-Fast Reads & Writes: State is stored on the same machine as your compute, so reads and writes are ultra-fast. No database round trips, no latency spikes. State is persisted to Rivet for long term storage, so it survives server restarts.
  • Realtime: Update state and broadcast changes in realtime with WebSockets. No external pub/sub systems, no polling – just built-in low-latency events.
  • Infinitely Scalable: Automatically scale from zero to millions of concurrent actors. Pay only for what you use with instant scaling and no cold starts.
  • Fault Tolerant: Built-in error handling and recovery. Actors automatically restart on failure while preserving state integrity and continuing operations.

When to Use Rivet Actors

  • AI agents & sandboxes: multi-step toolchains, conversation memory, sandbox orchestration.
  • Multiplayer or collaborative apps: CRDT docs, shared cursors, realtime dashboards, chat.
  • Workflow automation: background jobs, cron, rate limiters, durable queues, backpressure control.
  • Data-intensive backends: geo-distributed or per-tenant databases, in-memory caches, sharded SQL.
  • Networking workloads: WebSocket servers, custom protocols, local-first sync, edge fanout.

Minimal Project

Backend

index.ts

ts
import { actor, event, setup } from "rivetkit";

const counter = actor({
	state: { count: 0 },
	events: {
		count: event<number>(),
	},
	actions: {
		increment: (c, amount: number) => {
			c.state.count += amount;
			c.broadcast("count", c.state.count);
			return c.state.count;
		},
	},
});

export const registry = setup({
	use: { counter },
});

registry.start();

Client Docs

Use the client SDK that matches your app:

Actor Quick Reference

In-Memory State

Persistent data that survives restarts, crashes, and deployments. State is persisted on Rivet Cloud or Rivet self-hosted, so it survives restarts if the current process crashes or exits.

<Tabs> <Tab title="Static Initial State"> ```ts import { actor } from "rivetkit";

const counter = actor({ state: { count: 0 }, actions: { increment: (c) => c.state.count += 1, }, });

</Tab>
<Tab title="Dynamic Initial State">
```ts
import { actor } from "rivetkit";

interface CounterState {
  count: number;
}

const counter = actor({
  state: { count: 0 } as CounterState,
  createState: (c, input: { start?: number }): CounterState => ({
    count: input.start ?? 0,
  }),
  actions: {
    increment: (c) => c.state.count += 1,
  },
});
</Tab> </Tabs>

Documentation

Keys

Keys uniquely identify actor instances. Use compound keys (arrays) for hierarchical addressing:

ts
import { actor, setup } from "rivetkit";
import { createClient } from "rivetkit/client";

const chatRoom = actor({
	state: { messages: [] as string[] },
	actions: {
		getRoomInfo: (c) => ({ org: c.key[0], room: c.key[1] }),
	},
});

const registry = setup({ use: { chatRoom } });
const client = createClient<typeof registry>("http://localhost:6420");

// Compound key: [org, room]
client.chatRoom.getOrCreate(["org-acme", "general"]);

// Access key inside actor via c.key

Don't build keys with string interpolation like "org:${userId}" when userId contains user data. Use arrays instead to prevent key injection attacks.

Documentation

Input

Pass initialization data when creating actors. Input is only available in createState and onCreate, so store it in state if you need it later.

ts
import { actor, setup } from "rivetkit";
import { createClient } from "rivetkit/client";

const game = actor({
	state: { mode: "" },
	createState: (c, input: { mode: string }) => ({
		mode: input.mode, // Store input in state for later access
	}),
	actions: {
		getMode: (c) => c.state.mode,
	},
});

const registry = setup({ use: { game } });
const client = createClient<typeof registry>("http://localhost:6420");

// Client usage
const gameHandle = client.game.getOrCreate(["game-1"], {
	createWithInput: { mode: "ranked" },
});

Documentation

Temporary Variables

Temporary data that doesn't survive restarts. Use for non-serializable objects (event emitters, connections, etc).

<Tabs> <Tab title="Static Initial Vars"> ```ts import { actor } from "rivetkit";

const counter = actor({ state: { count: 0 }, vars: { lastAccess: 0 }, actions: { increment: (c) => { c.vars.lastAccess = Date.now(); return c.state.count += 1; }, }, });

</Tab>
<Tab title="Dynamic Initial Vars">
```ts
import { actor } from "rivetkit";

const counter = actor({
  state: { count: 0 },
  createVars: () => ({
    emitter: new EventTarget(),
  }),
  actions: {
    increment: (c) => {
      c.vars.emitter.dispatchEvent(new Event("change"));
      return c.state.count += 1;
    },
  },
});
</Tab> </Tabs>

Documentation

Actions

Actions are the primary way clients and other actors communicate with an actor.

ts
import { actor } from "rivetkit";

const counter = actor({
	state: { count: 0 },
	actions: {
		increment: (c, amount: number) => (c.state.count += amount),
		getCount: (c) => c.state.count,
	},
});

Documentation

Events & Broadcasts

Events enable real-time communication from actors to connected clients.

ts
import { actor, event } from "rivetkit";

const chatRoom = actor({
	state: { messages: [] as string[] },
	events: {
		newMessage: event<{ text: string }>(),
	},
	actions: {
		sendMessage: (c, text: string) => {
			// Broadcast to ALL connected clients
			c.broadcast("newMessage", { text });
		},
	},
});

Documentation

Connections

Access the current connection via c.conn or all connected clients via c.conns. Use c.conn.id or c.conn.state to securely identify who is calling an action. Connection state is initialized via connState or createConnState, which receives parameters passed by the client on connect.

<Tabs> <Tab title="Static Connection Initial State"> ```ts import { actor } from "rivetkit";

const chatRoom = actor({ state: {}, connState: { visitorId: 0 }, onConnect: (c, conn) => { conn.state.visitorId = Math.random(); }, actions: { whoAmI: (c) => c.conn.state.visitorId, }, });

</Tab>
<Tab title="Dynamic Connection Initial State">
```ts
import { actor } from "rivetkit";

const chatRoom = actor({
  state: {},
  // params passed from client
  createConnState: (c, params: { userId: string }) => ({
    userId: params.userId,
  }),
  actions: {
    // Access current connection's state and params
    whoAmI: (c) => ({
      state: c.conn.state,
      params: c.conn.params,
    }),
    // Iterate all connections with c.conns
    notifyOthers: (c, text: string) => {
      for (const conn of c.conns.values()) {
        if (conn !== c.conn) conn.send("notification", { text });
      }
    },
  },
});
</Tab> </Tabs>

Documentation

Queues

Use queues to process durable messages in order inside a run loop.

ts
import { actor, queue } from "rivetkit";

const counter = actor({
	state: { value: 0 },
	queues: {
		increment: queue<{ amount: number }>(),
	},
	run: async (c) => {
		for await (const message of c.queue.iter()) {
			c.state.value += message.body.amount;
		}
	},
});

Documentation

Workflows

Use workflows when your run logic needs durable, replayable multi-step execution.

ts
import { actor, queue } from "rivetkit";
import { workflow } from "rivetkit/workflow";

const worker = actor({
	state: { processed: 0 },
	queues: {
		tasks: queue<{ url: string }>(),
	},
	run: workflow(async (ctx) => {
		await ctx.loop("task-loop", async (loopCtx) => {
			const message = await loopCtx.queue.next("wait-task");

			await loopCtx.step("process-task", async () => {
				await processTask(message.body.url);
				loopCtx.state.processed += 1;
			});
		});
	}),
});

async function processTask(url: string): Promise<void> {
	const res = await fetch(url, { method: "POST" });
	if (!res.ok) throw new Error(`Task failed: ${res.status}`);
}

Documentation

Actor-to-Actor Communication

Actors can call other actors using c.client().

ts
import { actor, setup } from "rivetkit";

const inventory = actor({
	state: { stock: 100 },
	actions: {
		reserve: (c, amount: number) => {
			c.state.stock -= amount;
		},
	},
});

const order = actor({
	state: {},
	actions: {
		process: async (c) => {
			const client = c.client<typeof registry>();
			await client.inventory.getOrCreate(["main"]).reserve(1);
		},
	},
});

const registry = setup({ use: { inventory, order } });

Documentation

Scheduling

Schedule actions to run after a delay or at a specific time. Schedules persist across restarts, upgrades, and crashes.

ts
import { actor, event } from "rivetkit";

const reminder = actor({
	state: { message: "" },
	events: {
		reminder: event<{ message: string }>(),
	},
	actions: {
		// Schedule action to run after delay (ms)
		setReminder: (c, message: string, delayMs: number) => {
			c.state.message = message;
			c.schedule.after(delayMs, "sendReminder");
		},
		// Schedule action to run at specific timestamp
		setReminderAt: (c, message: string, timestamp: number) => {
			c.state.message = message;
			c.schedule.at(timestamp, "sendReminder");
		},
		sendReminder: (c) => {
			c.broadcast("reminder", { message: c.state.message });
		},
	},
});

Documentation

Destroying Actors

Permanently delete an actor and its state using c.destroy().

ts
import { actor } from "rivetkit";

const userAccount = actor({
	state: { email: "", name: "" },
	onDestroy: (c) => {
		console.log(`Account ${c.state.email} deleted`);
	},
	actions: {
		deleteAccount: (c) => {
			c.destroy();
		},
	},
});

Documentation

Lifecycle Hooks

Actors support hooks for initialization, background processing, connections, networking, and state changes. Use run for long-lived background loops, and exit cleanly on shutdown with c.aborted or c.abortSignal.

ts
import { actor, event, queue } from "rivetkit";

interface RoomState {
	users: Record<string, boolean>;
	name?: string;
}

interface RoomInput {
	roomName: string;
}

interface ConnState {
	userId: string;
	joinedAt: number;
}

const chatRoom = actor({
	state: { users: {} } as RoomState,
	vars: { startTime: 0 },
	connState: { userId: "", joinedAt: 0 } as ConnState,
	events: {
		stateChanged: event<RoomState>(),
	},
	queues: {
		work: queue<{ task: string }>(),
	},

	// State & vars initialization
	createState: (c, input: RoomInput): RoomState => ({
		users: {},
		name: input.roomName,
	}),
	createVars: () => ({ startTime: Date.now() }),

	// Actor lifecycle
	onCreate: (c) => console.log("created", c.key),
	onDestroy: (c) => console.log("destroyed"),
	onWake: (c) => console.log("actor started"),
	onSleep: (c) => console.log("actor sleeping"),
	run: async (c) => {
		for await (const message of c.queue.iter()) {
			console.log("processing", message.body.task);
		}
	},
	onStateChange: (c, newState) => c.broadcast("stateChanged", newState),

	// Connection lifecycle
	createConnState: (c, params): ConnState => ({
		userId: (params as { userId: string }).userId,
		joinedAt: Date.now(),
	}),
	onBeforeConnect: (c, params) => {
		/* validate auth */
	},
	onConnect: (c, conn) => console.log("connected:", conn.state.userId),
	onDisconnect: (c, conn) => console.log("disconnected:", conn.state.userId),

	// Networking
	onRequest: (c, req) => new Response(JSON.stringify(c.state)),
	onWebSocket: (c, socket) => socket.addEventListener("message", console.log),

	// Response transformation
	onBeforeActionResponse: <Out>(
		c: unknown,
		name: string,
		args: unknown[],
		output: Out,
	): Out => output,

	actions: {},
});

Documentation

Context Types

When writing helper functions outside the actor definition, use *ContextOf<typeof myActor> to extract the correct context type. Do not manually define your own context interface — always derive it from the actor definition.

ts
import { actor, ActionContextOf } from "rivetkit";

const gameRoom = actor({
	state: { players: [] as string[], score: 0 },
	actions: {
		addPlayer: (c, playerId: string) => {
			validatePlayer(c, playerId);
			c.state.players.push(playerId);
		},
	},
});

// Good: derive context type from actor definition
function validatePlayer(c: ActionContextOf<typeof gameRoom>, playerId: string) {
	if (c.state.players.includes(playerId)) {
		throw new Error("Player already in room");
	}
}

// Bad: don't manually define context types like this
// type MyContext = { state: { players: string[] }; ... };

Documentation

Errors

Use UserError to throw errors that are safely returned to clients. Pass metadata to include structured data. Other errors are converted to generic "internal error" for security.

<Tabs> <Tab title="Actor"> ```ts import { actor, UserError } from "rivetkit";

const user = actor({ state: { username: "" }, actions: { updateUsername: (c, username: string) => { if (username.length < 3) { throw new UserError("Username too short", { code: "username_too_short", metadata: { minLength: 3, actual: username.length }, }); } c.state.username = username; }, }, });

</Tab>
<Tab title="Client">
```ts
import { actor, setup } from "rivetkit";
import { createClient, ActorError } from "rivetkit/client";

const user = actor({
  state: { username: "" },
  actions: { updateUsername: (c, username: string) => { c.state.username = username; } }
});

const registry = setup({ use: { user } });
const client = createClient<typeof registry>("http://localhost:6420");

try {
  await client.user.getOrCreate([]).updateUsername("ab");
} catch (error) {
  if (error instanceof ActorError) {
    console.log(error.code);     // "username_too_short"
    console.log(error.metadata); // { minLength: 3, actual: 2 }
  }
}
</Tab> </Tabs>

Documentation

Low-Level HTTP & WebSocket Handlers

For custom protocols or integrating libraries that need direct access to HTTP Request/Response or WebSocket connections, use onRequest and onWebSocket.

HTTP Handler Documentation · WebSocket Handler Documentation

Icons & Names

Customize how actors appear in the UI with display names and icons. It's recommended to always provide a name and icon to actors in order to make them easier to distinguish in the dashboard.

typescript
import { actor } from "rivetkit";

const chatRoom = actor({
	options: {
		name: "Chat Room",
		icon: "💬", // or FontAwesome: "comments", "chart-line", etc.
	},
	// ...
});

Documentation

Client Documentation

Find the full client guides here:

Common Patterns

Actors scale naturally through isolated state and message-passing. Structure your applications with these patterns:

Documentation

Actor Per Entity

Create one actor per user, document, or room. Use compound keys to scope entities:

<CodeGroup workspace> ```ts client.ts import { createClient } from "rivetkit/client"; import type { registry } from "./index";

const client = createClient<typeof registry>("http://localhost:6420");

// Single key: one actor per user client.user.getOrCreate(["user-123"]);

// Compound key: document scoped to an organization client.document.getOrCreate(["org-acme", "doc-456"]);


```ts index.ts
import { actor, setup } from "rivetkit";

export const user = actor({
  state: { name: "" },
  actions: {},
});

export const document = actor({
  state: { content: "" },
  actions: {},
});

export const registry = setup({ use: { user, document } });

registry.start();
</CodeGroup>

Coordinator & Data Actors

Data actors handle core logic (chat rooms, game sessions, user data). Coordinator actors track and manage collections of data actors—think of them as an index.

<CodeGroup workspace> ```ts index.ts import { actor, setup } from "rivetkit";

// Coordinator: tracks chat rooms within an organization export const chatRoomList = actor({ state: { rooms: [] as string[] }, actions: { addRoom: async (c, name: string) => { // Create the chat room actor const client = c.client<typeof registry>(); await client.chatRoom.create([c.key[0], name]); c.state.rooms.push(name); }, listRooms: (c) => c.state.rooms, }, });

// Data actor: handles a single chat room export const chatRoom = actor({ state: { messages: [] as string[] }, actions: { send: (c, msg: string) => { c.state.messages.push(msg); }, }, });

export const registry = setup({ use: { chatRoomList, chatRoom } });

registry.start();


```ts client.ts
import { createClient } from "rivetkit/client";
import type { registry } from "./index";

const client = createClient<typeof registry>("http://localhost:6420");

// Coordinator per org
const coordinator = client.chatRoomList.getOrCreate(["org-acme"]);
await coordinator.addRoom("general");
await coordinator.addRoom("random");

// Access chat rooms created by coordinator
client.chatRoom.get(["org-acme", "general"]);
</CodeGroup>

Run Loop

Use a run loop for continuous background work inside an actor. Process queue messages in order, run logic on intervals, stream AI responses, or coordinate long-running tasks.

ts
import { actor, queue, setup } from "rivetkit";

const counterWorker = actor({
	state: { value: 0 },
	queues: {
		mutate: queue<{ delta: number }>(),
	},
	run: async (c) => {
		for await (const message of c.queue.iter()) {
			c.state.value += message.body.delta;
		}
	},
	actions: {
		getValue: (c) => c.state.value,
	},
});

const registry = setup({ use: { counterWorker } });

Workflow Loop

Use this pattern for long-lived, durable workflows that initialize resources, process commands in a loop, then clean up.

ts
import { actor, queue, setup } from "rivetkit";
import { Loop, workflow } from "rivetkit/workflow";

type WorkMessage = { amount: number };
type ControlMessage = { type: "stop"; reason: string };

const worker = actor({
	state: {
		phase: "idle" as "idle" | "running" | "stopped",
		processed: 0,
		total: 0,
		stopReason: null as string | null,
	},
	queues: {
		work: queue<WorkMessage>(),
		control: queue<ControlMessage>(),
	},
	run: workflow(async (ctx) => {
		await ctx.step("setup", async () => {
			await fetch("https://api.example.com/workers/init", {
				method: "POST",
			});
			ctx.state.phase = "running";
			ctx.state.stopReason = null;
		});

		const stopReason = await ctx.loop("worker-loop", async (loopCtx) => {
			const message = await loopCtx.queue.next("wait-command", {
				names: ["work", "control"],
			});

			if (message.name === "work") {
				await loopCtx.step("apply-work", async () => {
					await fetch("https://api.example.com/workers/process", {
						method: "POST",
						body: JSON.stringify({ amount: message.body.amount }),
					});
					loopCtx.state.processed += 1;
					loopCtx.state.total += message.body.amount;
				});
				return;
			}

			return Loop.break((message.body as ControlMessage).reason);
		});

		await ctx.step("teardown", async () => {
			await fetch("https://api.example.com/workers/shutdown", {
				method: "POST",
			});
			ctx.state.phase = "stopped";
			ctx.state.stopReason = stopReason;
		});
	}),
});

const registry = setup({ use: { worker } });

Documentation

Actions vs Queues

  • Actions are not durable. Use them for realtime reads, ephemeral data, and low-latency communication like player input.
  • Queues are durable. Use them to serialize mutations through the run loop, avoiding race conditions with SQLite and other local state. Callers can still wait for a response from queued work.

Authentication, Security, & CORS

  • Validate credentials in onBeforeConnect or createConnState and throw an error to reject unauthorized connections.
  • Use c.conn.state to securely identify users in actions rather than trusting action parameters.
  • For cross-origin access, validate the request origin in onBeforeConnect.

Authentication Documentation · CORS Documentation

Versions & Upgrades

When deploying new code, set a version number so Rivet can route new actors to the latest runner and optionally drain old ones. Use a build timestamp, git commit count, or CI build number as the version. It is very important to configure versioning before deploying to production. Without versioning, actors can regress by running on older runner versions, and existing actors will never be forced to migrate to new runners. They will continue running indefinitely on the old runners until they exit.

Documentation

Anti-Patterns

Never build a "god" actor

Do not put all your logic in a single actor. A god actor serializes every operation through one bottleneck, kills parallelism, and makes the entire system fail as a unit. Split into focused actors per entity.

Never create an actor per request

Actors are long-lived and maintain state across requests. Creating a new actor for every incoming request throws away the core benefit of the model and wastes resources on actor creation and teardown. Use actors for persistent entities and regular functions for stateless work.