SMS agent

SMS gives people a plain-text way to use your product. Flow can send through a Flow Messaging SMS sender or through your existing provider.

Connect a sender

SMS is not a flow link --channel trial option. Set up your own SMS sender and credentials. With Flow Messaging, set FLOW_MESSAGING_KEY and FLOW_MESSAGING_SMS_SENDER.

Add the channel explicitly: the starter’s fm.channels() does not automatically include SMS. In the starter’s src/main.ts, replace its channels assignment with:

src/main.ts — replace the channels assignment

const channels = fm ? [...fm.channels(), fm.sms()] : [];

The existing buildAgent({ channels, ... }) call and fm.start connection then include SMS. For production persistence and startup, follow Self-hosting.

Check it worked: send a message to your own SMS number and verify the reply and tool event.

Use your own provider

This configuration fragment adapts a provider client you supply:

Channel configuration fragment

import { sms } from "@flow-engineer/flow";

const channel = sms({
  sendMessage: (to, message) =>
    smsClient.send(to, message.text, message.idempotencyKey),
});

Pass channel to your agent. Verify your provider’s incoming webhook, then call agent.message({ channel: "sms", from, message: text, messageId }) with its trusted fields. Preserve the idempotency key in your provider’s send operation when supported.

What changes on SMS

SMS uses plain-text segments, without buttons, typing indicators or read receipts. Phone identities are normalized; configure defaultCountryCode if your provider sends national numbers. Flow’s channel rules handle STOP, START and HELP—keep consent and opt-outs consistent with your provider and sender configuration.