Populate Retell dynamic variables with Google Sheets data for call handling

Overview - This workflow provides Retell agent builders with a simple way to populate dynamic variables using n8n. - The workflow fetches user information from a Google Sheet based on the phone number and sends it back to Retell. - It is based on Retell's Inbound Webhook Call. - Retell is a service that lets you create Voice Agents that handle voice calls simply, based on a prompt or using a conversational flow builder. Who is it for For builders of Retell's Voice Agents who want to make their agents more personalized. Prerequisites - Have a Retell AI Account - Create a Retell agent - Purchase a phone number and associate it with your agent - Create a Google Sheets - for example, make a copy of this one. - Your Google Sheet must have at least one column with the phone number. The remaining columns will be used to populate your Retell agent’s dynamic variables. - All fields are returned as strings to Retell (variables are replaced as text) How it works - The webhook call is received from Retell. We filter the call using their whitelisted IP address. - It extracts data from the webhook call and uses it to retrieve the user from Google Sheets. - It formats the data in the response to match Retell's expected format. - Retell uses this data to replace dynamic variables in the prompts. How to use it See the description for screenshots! - Set the webhook name (keep it as POST). - Copy the Webhook URL (e.g., and paste it into Retell's interface. Navigate to "Phone Numbers", click on the phone number, and enable "Add an inbound webhook". - In your prompt (e.g., "welcome message"), use the variable with this syntax: {{variablename}} (see Retell's documentation). - These variables will be dynamically replaced by the data in your Google Sheet. Notes - In Google Sheets, the phone number must start with '+. - Phone numbers must be formatted like the example: with the +, extension, and no spaces. - You can use any database—just replace Google Sheets with your own, making sure to keep the phone number formatting consistent. 👉 Reach out to us if you're interested in analysing your Retell Agent conversations.