Realtime in ten lines

Kumo is a realtime messaging SDK. Open a channel, publish a message, and every connected client gets it in under 50 milliseconds, anywhere on earth.

Installation #

Kumo works in the browser, Node 18+, Bun, Deno and React Native. Pick your package manager.

$ npm install @kumo/sdk

Quickstart #

1. Create a client

   Grab a publishable key from the dashboard. It is safe to ship in frontend code.

2. Join a channel

   Channels are created on first use. Name them anything, like room:lobby.

3. Publish and subscribe

   Every subscriber receives the message, including the sender.

import { Kumo } from '@kumo/sdk' const kumo = new Kumo({ key: 'pk_live_7c1e...', region: 'auto' })const room = kumo.channel('room:lobby') room.subscribe('message', (msg) => {  console.log(msg.data.text, 'from', msg.clientId)}) await room.publish('message', { text: 'Hello from Rajshahi' })// latency p50: 38 ms, p99: 91 ms

Authentication #

Publishable keys can subscribe. To publish from untrusted clients, mint a short-lived token on your server with the scopes the user needs.

const token = await kumo.auth.createToken({  clientId: user.id,  scopes: ['room:*:publish', 'room:*:presence'],  ttl: 3600 // seconds})

Channels #

A channel is a named stream of messages. Names use colons for namespaces, and scopes can match with wildcards like room:*.

Presence #

Presence tells you who is in a channel right now. Use it for online dots, live cursors and "typing" hints.

Message history #

Channels keep the last 24 hours of messages by default. Call room.history({ limit: 50 }) to backfill a chat window.

Edge regions #

Kumo runs in 41 regions. With region: 'auto', each client connects to the closest one and messages cross the backbone, not the public internet.

publish() #

Sends a message to every subscriber of the channel. Returns when the message is stored in at least two regions.

subscribe() #

Registers a listener. Returns an unsubscribe function. Reconnects and replays missed messages for you.

Try it live #

This runs against a simulated sandbox right in your browser. Change the fields and press Send.

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Errors #