Unified Messaging API

Bring your existing agent to the apps people already use. Flow Messaging gives it one HTTP API and event format for WhatsApp, iMessage and Telegram, with SDKs for TypeScript and Python. Keep your model and tools. Receive a message, run your agent and reply to the same conversation; Flow handles channel delivery and sending rules.

Receive and reply

TypeScript

import { FlowMessaging, contentText } from "@flow-engineer/messaging";

const flow = new FlowMessaging(); // reads FLOW_MESSAGING_KEY

for await (const event of flow.events.stream({ types: ["message.received"] })) {
  const said = contentText(event.data.message.content);
  await event.conversation.reply("You said: " + said, {
    idempotencyKey: event.id,
  });
}

Install with npm install @flow-engineer/messaging. The quickstart gets you a test key and a Telegram sandbox conversation before running this loop. Check it worked: send a message from your phone and receive it back as “You said: …”.

The API is V0, at /v0, with one endpoint per message kind. Code written for /v1: see Moving from /v1.

Choose a channel

Start on the shared sandbox, then connect your own bot.

Connect your own number with a live key.

iMessage

Try Flow’s shared line free, then get a line of your own.

The Telegram sandbox is available for testing. Flow’s shared iMessage line comes with the free trial your first sign-in at flow.engineer starts; dedicated iMessage lines, with group chats and SMS and RCS from the same number, are set up with the Flow team. The shared WhatsApp sandbox is not open to test keys. The US SMS/MMS channel is in pilot, not general availability. GET /v0/senders tells you which senders your key can use.

What Flow handles

You do	Flow does
Receive events	Delivers one event format through signed webhooks, a live stream or polling
Reply into a conversation	Uses that conversation’s sender and channel
Send one kind per endpoint	Sends exactly that, or refuses it with `422` and a hint; converts nothing
Retry with the same key	Deduplicates the API request
Follow delivery events	Reports sent or failed, plus delivered and read where supported

See sending rules for reply windows, pacing and new-contact budgets. These rules apply whether you send over HTTP, a stream or a webhook response.

Pick your integration

Use an SDK or HTTP

TypeScript, Python or any language that makes HTTP requests.

Use your agent framework

Connect an existing agent without changing its model or tools.

Build with a coding agent

Setup instructions, a skill and an optional development MCP.

Build on Flow Framework

Use Flow’s conversation runtime as well as the messaging connection.

The SDKs are open source under Apache-2.0 in flow-engineer/sdk. The HTTP API is versioned by date; pin a version for production.

Get started

Observe

Test before you ship

Concepts

Channel guides

Agent frameworks

Compare

HTTP API

Unified Messaging API

Receive and reply

Choose a channel

Telegram

WhatsApp

iMessage

What Flow handles

Pick your integration

Use an SDK or HTTP

Use your agent framework

Build with a coding agent

Build on Flow Framework

​Receive and reply

​Choose a channel

Telegram

WhatsApp

iMessage

​What Flow handles

​Pick your integration

Use an SDK or HTTP

Use your agent framework

Build with a coding agent

Build on Flow Framework

Receive and reply

Choose a channel

What Flow handles

Pick your integration