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.

By Berend Vrakking, founder of Product Metrics. Updated 7 October 2026.

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

Keep reading

Custom labelsThe attributes a supplemental feed can fill with your own values.
Product feedThe primary source a supplemental feed adds to.
Google Merchant CenterWhere data sources are set up.
Product SegmentationSee each product in one of six segments, by volume and return.
What is Google Merchant Center? An advertiser’s guideWhere supplemental data sources sit in Merchant Center, and what needs the add-on.