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 1. Copy the webhook URL (e.g. 2. Modify the Retell Custom Function webhook URL (see template description for screenshots) - Edit the function - Modify the URL 3. Modify the logic in the Set node or replace it with your own custom flow 4. 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.