# Twilio personalization
## Overview
When receiving inbound Twilio calls, you can dynamically fetch conversation initiation data through a webhook. This allows you to customize your agent’s behavior based on caller information and other contextual data.
For when the webhook fires and the request shape, see [Conversation initiation webhooks](/guides/elevenagents-customization-personalization#conversation-initiation-webhooks).
https://www.youtube-nocookie.com/embed/cAuSo8qNs-8?rel=0
## How it works
1. When a Twilio call is received, ElevenAgents will make a webhook call to your specified endpoint, passing call information (`caller_id`, `agent_id`, `called_number`, `call_sid`, `conversation_id`) as arguments
2. Your webhook returns conversation initiation client data, including dynamic variables and overrides (an example is shown below)
3. This data is used to initiate the conversation
:::callout{intent="tip"}
The system uses Twilio’s connection/dialing period to fetch webhook data in parallel, creating a seamless experience where:
- Users hear the expected telephone connection sound
- In parallel, ElevenAgents fetches necessary webhook data
- The conversation is initiated with the fetched data by the time the audio connection is established
:::
## Configuration
:::::steps
:::step{title="Configure webhook details"}
In the [settings page](https://elevenlabs.io/app/agents/settings) of ElevenAgents, configure the webhook URL and add any secrets needed for authentication.
Click on the webhook to modify which secrets are sent in the headers.
:::
:::step{title="Enable fetching conversation initiation data"}
In the “Security” tab of the [agent’s page](https://elevenlabs.io/app/agents/agents/), enable fetching conversation initiation data for inbound Twilio calls, and define fields that can be overridden.
:::
:::step{title="Implement the webhook endpoint to receive Twilio data"}
The webhook will receive a POST request with the following parameters:
| Parameter | Type | Description |
| ----------------- | ------ | -------------------------------------- |
| `caller_id` | string | The phone number of the caller |
| `agent_id` | string | The ID of the agent receiving the call |
| `called_number` | string | The Twilio number that was called |
| `call_sid` | string | Unique identifier for the Twilio call |
| `conversation_id` | string | ElevenLabs conversation identifier |
:::
::::step{title="Return conversation initiation client data"}
Your webhook must return a JSON response containing the initiation data for the agent.
:::callout{intent="info"}
The `dynamic_variables` field must contain all dynamic variables defined for the agent. Overrides on the other hand are entirely optional. For more information about dynamic variables and overrides see the [dynamic variables](/guides/elevenagents-customization-personalization-dynamic-variables) and [overrides](/guides/elevenagents-customization-personalization-overrides) docs.
:::
An example response could be:
```json
{
"type": "conversation_initiation_client_data",
"conversation_config_override": {
"agent": {
"prompt": {
"prompt": "The customer's bank account balance is $100. They are based in San Francisco.",
"llm": "gpt-5.6-luna"
},
"first_message": "Hi, how can I help you today?",
"language": "en"
},
"tts": {
"voice_id": "new-voice-id"
},
"conversation": {
"text_only": false
}
},
"dynamic_variables": {
"customer_name": "John Doe",
"account_status": "premium",
"last_interaction": "2026-01-15"
},
"branch_id": "agtbrch_xxxx",
"environment": "production"
}
```
::::
:::::
ElevenAgents will use the dynamic variables to populate the conversation initiation data, and the conversation will start smoothly.
:::callout{intent="warning"}
Ensure your webhook responds within a reasonable timeout period to avoid delaying the call handling.
:::
## Security
- Use HTTPS endpoints only
- Implement authentication using request headers
- Store sensitive values as secrets through the [ElevenLabs secrets manager](https://elevenlabs.io/app/agents/settings)
- Validate the incoming request parameters
## Related pages
- [Administration](./administration-index.md)
- [API reference](./api-reference-index.md)
- [Changelog](./changelog-index.md)
- [ElevenAgents](./elevenagents-index.md)
- [ElevenAPI](./elevenapi-index.md)
- [ElevenCreative](./elevencreative-index.md)
- [ElevenLabs Documentation Docs](../index.md)
- [General Troubleshooting FAQ](./troubleshooting-index.md)
- [General Website FAQ](./website-index.md)
- [Help Center](./help-center-2-index.md)
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