# STOP means stop, automatically.

Every recipient can text STOP to opt out, HELP to get a help response, and START to opt back in. Bird honors these keywords automatically on every send and keeps a per-recipient suppression list you can query — no extra code on your side.

## Opt-out is the one rule that's always on.

Opt-out handling is part of SMS compliance on the Bird SMS API, and unlike registration it applies everywhere you send, with no setup. The reserved keywords STOP, HELP, and START are recognized in inbound messages and acted on per recipient, so a person who opts out stays opted out across your sends until they choose to come back.

## How the keywords behave.

Reserved keywords, enforced per recipient.

## An opt-out arrives as a signed event.

When a recipient opts out, Bird suppresses them and notifies your webhook with an sms.opted_out event so your own records stay in sync. The event is HMAC-signed like every Bird webhook.

## Opt-out is an inbound flow.

STOP, HELP, and START arrive the same way any reply does — as inbound messages on two-way numbers. Bird intercepts the reserved keywords and acts on them before they reach your application logic, so you get the suppression behavior for free and still see everything else your recipients send.

## Honor every opt-out without writing a handler.

Opt-out is one regime of SMS compliance on Bird. STOP, HELP, and START are enforced on every send, with a suppression list you can query from the same API.