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.