Connect Retell Voice Agents to Custom Functions

Overview This workflow allows you to trigger custom logic in n8n directly from Retell's Voice Agent using Custom Functions. It captures a POST webhook from Retell every time a Voice Agent reaches a Custom Function node. You can plug in any logic—call an external API, book a meeting, update a CRM, or even return a dynamic response back to the agent.

Who is it for For builders using Retell who want to extend Voice Agent functionality with real-time custom workflows or AI-generated responses.

Prerequisites Have a Retell AI Account A Retell agent with a Custom Function node in its conversation flow (see template below) Set your n8n webhook URL in the Custom Function configuration (see "How to use it" below) (Optional) Familiarity with Retell's Custom Function docs Start a conversation with the agent (text or voice)

Retell Agent Example To get you started, we've prepared a Retell Agent ready to be imported, that includes the call to this template. Import the agent to your Retell workspace (top-right button on your agent's page) You will need to modify the function URL in order to call your own instance. This template is a simple hotel agent that calls the custom function to confirm a booking, passing basic formatted data.

How it works Retell sends a webhook to n8n whenever a Custom Function is triggered during a call (or test chat). The webhook includes: Full call context (transcript, call ID, etc.) Parameters defined in the Retell function node You can process this data and return a response string back to the Voice Agent in real-time.

How to use it Copy the webhook URL (e.g. https://your-instance.app.n8n.cloud/webhook/hotel-retell-template) Modify the Retell Custom Function webhook URL (see template description for screenshots) Edit the function

Modify the URL

Modify the logic in the Set node or replace it with your own custom flow Deploy and test: Retell will hit your n8n workflow during the conversation

Extension Ideas Call a third-party API to fetch data (e.g. hotel availability, CRM records) Use an LLM node to generate dynamic responses Trigger a parallel automation (Slack message, calendar invite, etc.)

👉 Reach out to us if you're interested in analyzing your Retell Agent conversations.