> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sendo.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Keywords

> Understand STOP/START/HELP keywords.

Keywords are special words that can be used to opt-in or opt-out of messaging from your campaign. They are used to comply with the [CTIA guidelines](https://api.ctia.org/wp-content/uploads/2023/05/230523-CTIA-Messaging-Principles-and-Best-Practices-FINAL.pdf) for SMS messaging.

Sendo automatically handles the processing of these keywords, so you don't have to worry about this. When a campaign is created, we set default keywords for `STOP`, `START` and `HELP` requests. You can change these keywords, and the message that is sent back to a contact in response, at any time from your campaign settings page.

### STOP keywords

When a contact sends a message containing the `STOP` keyword, they will be opted out of all future messages from your campaign. They will receive a confirmation message in response, which you can customize from your campaign settings page. All future message to this user will fail with a `1310` error code, unless that contact opts back in.

<Warning>The `STOP` keyword cannot be removed, but additional variations can be added.</Warning>

**Default response:** "NETWORK MSG: You will no longer receive messages from this number. Reply START to subscribe again."

### START keywords

When a contact sends a message containing the `START` keyword, they will be opted back in to your campaign. They will receive a confirmation message in response, which you can modify from your campaign settings page. This keyword can be customized.

**Default response:** "NETWORK MSG: You've subscribed to receive messages from this number. Reply STOP to unsubscribe."

### HELP keywords

When a contact sends a message containing the `HELP` keyword, they will receive a message with instructions on how to opt-in or opt-out of your campaign. This keyword can be customized, and <Tooltip tip="For example, you can add an email address for support requests or a help center link to the message.">additional information</Tooltip> can be added to the response message.

**Default response:** "NETWORK MSG: Text STOP to unsubscribe. Text START to reactivate your subscription if you have opted out."