RivetKit JavaScript Client

Use this skill when building JavaScript clients (browser, Node.js, or Bun) that connect to Rivet Actors with rivetkit/client.

First Steps

1. Install the client (latest: 2.2.0)

   npm install rivetkit@2.2.0
   

2. Create a client with createClient() and call actor actions.

Error Handling Policy

• Prefer fail-fast behavior by default.
• Avoid try/catch unless absolutely needed.
• If a catch is used, handle the error explicitly, at minimum by logging it.

Getting Started

See the backend quickstart guide for getting started.

Minimal Client

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

const client = createClient<typeof registry>({
  endpoint: "https://my-namespace:pk_...@api.rivet.dev",
});
const counter = client.counter.getOrCreate(["my-counter"]);
const count = await counter.increment(1);

import { actor, setup } from "rivetkit";

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

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

registry.start();

Stateless vs Stateful

import { createClient } from "rivetkit/client";

const client = createClient();
const handle = client.counter.getOrCreate(["my-counter"]);

// Stateless: each call is independent
await handle.increment(1);

// Stateful: keep a connection open for realtime events
const conn = handle.connect();
conn.on("count", (value) => console.log(value));
await conn.increment(1);

Getting Actors

import { createClient } from "rivetkit/client";

const client = createClient();
const room = client.chatRoom.getOrCreate(["room-42"]);
const existing = client.chatRoom.get(["room-42"]);

const created = await client.game.create(["game-1"], {
  input: { mode: "ranked" },
});

const byId = client.chatRoom.getForId("actor-id");
const resolvedId = await room.resolve();

Connection Parameters

import { createClient } from "rivetkit/client";

const client = createClient();
const chat = client.chatRoom.getOrCreate(["general"], {
  params: { authToken: "jwt-token-here" },
});

const conn = chat.connect();

import { createClient } from "rivetkit/client";

async function getAuthToken(): Promise<string> {
  return "jwt-token-here";
}

const client = createClient();
const chat = client.chatRoom.getOrCreate(["general"], {
  getParams: async () => ({
    authToken: await getAuthToken(),
  }),
});

const conn = chat.connect();

Use params for static connection parameters. Use getParams when the value can change between connection attempts, such as refreshing a JWT before each .connect() or reconnect.

Subscribing to Events

import { createClient } from "rivetkit/client";

const client = createClient();
const conn = client.chatRoom.getOrCreate(["general"]).connect();
conn.on("message", (msg) => console.log(msg));
conn.once("gameOver", () => console.log("done"));

Connection Lifecycle

import { createClient } from "rivetkit/client";

const client = createClient();
const conn = client.chatRoom.getOrCreate(["general"]).connect();

conn.onOpen(() => console.log("connected"));
conn.onClose(() => console.log("disconnected"));
conn.onError((err) => console.error("error:", err));
conn.onStatusChange((status) => console.log("status:", status));

await conn.dispose();

Low-Level HTTP & WebSocket

For actors that implement onRequest or onWebSocket, call them directly:

import { createClient } from "rivetkit/client";

const client = createClient();
const handle = client.chatRoom.getOrCreate(["general"]);

const response = await handle.fetch("history");
const history = await response.json();

const ws = await handle.webSocket("stream");
ws.addEventListener("message", (event) => {
  console.log("message:", event.data);
});
ws.send("hello");

Calling from Backend

import { Hono } from "hono";
import { createClient } from "rivetkit/client";

const app = new Hono();
const client = createClient();

app.post("/increment/:name", async (c) => {
  const counterHandle = client.counter.getOrCreate([c.req.param("name")]);
  const newCount = await counterHandle.increment(1);
  return c.json({ count: newCount });
});

Error Handling

import { ActorError } from "rivetkit/client";
import { createClient } from "rivetkit/client";

const client = createClient();

try {
  await client.user.getOrCreate(["user-123"]).updateUsername("ab");
} catch (error) {
  if (error instanceof ActorError) {
    console.log(error.code, error.metadata);
  }
}

Concepts

Keys

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

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

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

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

import { actor, setup } from "rivetkit";

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

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

registry.start();

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

Environment Variables

createClient() automatically reads:

• RIVET_ENDPOINT (endpoint)
• RIVET_NAMESPACE
• RIVET_TOKEN
• RIVET_RUNNER

Defaults to http://localhost:6420 when unset. RivetKit runs on port 6420 by default.

Endpoint Format

Endpoints support URL auth syntax:

https://namespace:token@api.rivet.dev

You can also pass the endpoint without auth and provide RIVET_NAMESPACE and RIVET_TOKEN separately. For serverless deployments, use your app's /api/rivet URL. See Endpoints for details.

API Reference

Package: rivetkit

See the RivetKit client overview.

• createClient - Create a client
• createEngineDriver - Engine driver
• DriverConfig - Driver configuration
• Client - Client type

Need More Than the Client?

If you need more about Rivet Actors, registries, or server-side RivetKit, add the main skill:

npx skills add rivet-dev/skills

Then use the rivetkit skill for backend guidance.