---
title: "Merchant Center supplemental feed | Product Metrics"
description: "A Merchant Center supplemental feed adds to or overrides product data from your primary feed, such as custom labels, titles or a missing GTIN. See an example."
canonical: "https://www.productmetrics.io/glossary/supplemental-feed"
pageType: article
language: en
publisher: "Product Metrics"
author: "Berend Vrakking"
datePublished: 2026-10-07
dateModified: 2026-10-07
---

> Content index: https://www.productmetrics.io/llms.txt

# Supplemental feed (Google Merchant Center)

A Google Merchant Center supplemental feed is a secondary data source that adds details to, or overrides details in, the products of your primary feed.

## Example

Two supplemental rows, one of them ignored:

| id | Primary feed | Supplemental feed | In Merchant Center |
| --- | --- | --- | --- |
| TR2-BLK-42 | custom_label_0: empty | custom_label_0: stars | custom_label_0: stars |
| WB-BRN-44 | custom_label_0: empty | custom_label_0: dogs | custom_label_0: dogs |
| ZZ-000 | Not in the primary feed | custom_label_0: stars | No change, the ID is not in the primary feed |

Rows match products by ID. ZZ-000 has no product in the primary feed to match, so it changes nothing. Illustrative data.

## For one product, and for an account

A supplemental feed works one product at a time: a row finds its product by ID and changes only the attributes it lists, from custom labels and titles to a missing GTIN.

Google’s help pages now call it a supplemental data source, and say product data is updated only when the supplemental source contains IDs that are in a primary data source.

This is the route Product Metrics uses for its segment label. Your primary feed is left as it was, and your campaigns can pick up the label from there.

## Common mistake

A typo in the ID column. The row then matches no product in the primary feed, so it changes nothing, and the label you expected never appears.

## Questions

### What is a supplemental feed in Google Merchant Center?

It is a secondary data source you add next to your primary feed. Google describes it as a way to provide more details, or update existing ones, for products that already exist in the primary feed.

### Can a supplemental feed add new products?

No. Google says a supplemental data source can’t be used to add or remove products, or as a standalone data source. Only a primary data source can add or remove products.

### What can a supplemental feed change?

Google lists six uses: add or override custom labels, add or override promotion IDs, override titles, exclude specific products, add a missing GTIN and add local inventory product data. A product matches its row through its ID.

## Sources

- [Google Merchant Center Help: About supplemental data sources](https://support.google.com/merchants/answer/15157604)
- [Google Merchant Center Help: Create a data source](https://support.google.com/merchants/answer/14990942)

## Keep reading

- [Custom labels](https://www.productmetrics.io/glossary/custom-labels): The attributes a supplemental feed can fill with your own values.
- [Product feed](https://www.productmetrics.io/glossary/product-feed): The primary source a supplemental feed adds to.
- [Google Merchant Center](https://www.productmetrics.io/glossary/google-merchant-center): Where data sources are set up.
- [Product Segmentation](https://www.productmetrics.io/product-segmentation): See each product in one of six segments, by volume and return.
- [What is Google Merchant Center? An advertiser’s guide](https://www.productmetrics.io/blog/what-is-google-merchant-center): Where supplemental data sources sit in Merchant Center, and what needs the add-on.

---

Written by Berend Vrakking, founder of Product Metrics. Last updated 2026-10-07.

HTML version: https://www.productmetrics.io/glossary/supplemental-feed