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., https://your-instance.app.n8n.cloud/webhook/retell-dynamic-variables) 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: {{variable_name}} (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.