Supplemental Feeds in Google Merchant Center Explained

Most stores get their product data from a platform app or a single export file. That primary source rarely has everything: GTINs live in another system, titles need rewriting, or certain products need excluding from ads. A supplemental data source (often called a supplemental feed) fills those gaps.

This guide explains what supplemental sources can and can’t do, the add-on you need to use them, how products are matched, how they interact with attribute rules and the “Take latest” operation, and how regional inventory sources and multi-client accounts fit in.

What a supplemental data source is

Google’s data source documentation separates primary and supplemental sources:

	Primary data source	Supplemental data source
Adds or removes products	Yes (the only type that can)	No
Updates attributes	Yes	Yes, for existing products
Stands alone	Yes	No; linked to a primary source
Sets country and language targeting	Yes	No
Matches products by	n/a	Exact ID; feed label must match

A supplemental source is a list of IDs plus the attributes you want to add or change. When Merchant Center processes it, it finds the product with the same ID in the primary source and applies the values. For more on the overall structure, see what is a product feed.

Before you start: the add-on requirement

In Merchant Center, the “Supplemental sources” tab is visible only when the Advanced data source management add-on is enabled. You turn it on under Settings > Add-ons. The same add-on is needed for attribute rules and for creating data sources with custom feed labels.

Supplemental and primary sources live under Settings > Data sources. You create a supplemental source from the Supplemental sources tab in your Merchant Center account. If you’re new to data sources, how to add products to Merchant Center covers the basics.

How product matching works

Matching is where most supplemental sources fail. Google matches by ID exactly, and the feed label must match the primary source.

IDs must match exactly

The ID in your supplemental file must be the same string as the ID in the primary source. Google’s ID documentation warns not to rely on casing: “abc123” and “ABC123” may be confused, including in supplemental matching. Watch for whitespace and invisible characters too.

Common reasons IDs don’t match:

• The platform app builds IDs with a prefix or country code (for example a store or channel prefix plus a product and variant number), and the supplemental file uses the plain SKU.
• Spreadsheet software strips leading zeros or converts long numbers to scientific notation.
• Trailing spaces or non-printing characters copied from another system.
• The supplemental file uses parent IDs while the primary source uses variant IDs.

Practitioner tip: download the product list from Merchant Center and copy IDs from there, rather than from your store admin. That way you use the IDs Google actually holds.

Feed labels must match

Feed labels group products for campaigns. A supplemental source only applies to products with the same feed label. Feed labels are up to 20 characters (uppercase A to Z, 0 to 9, hyphens and underscores, no spaces), and a data source’s language and feed label can’t be changed after creation, so check them before you build anything on top.

What supplemental sources can’t do

• Add products. Rows with IDs that aren’t in a primary source don’t create products. New products have to enter through the primary source.
• Remove products. Leaving a product out of a supplemental file doesn’t remove it. To hide products, use excluded_destination or pause; to remove them, remove them from the primary source.
• Stand alone. A supplemental source without a primary source does nothing.
• Change targeting. Countries, language and feed label are set by the primary source.

Setting up a supplemental source

1. Enable the Advanced data source management add-on under Settings > Add-ons.
2. Download your current products from Merchant Center so you have the exact IDs Google holds.
3. Build the supplemental file or sheet: an id column plus only the attributes you want to add or change.
4. In Settings > Data sources, open the Supplemental sources tab and add the source.
5. Link it to the primary source (and feed label) whose products it should update.
6. Check the attribute rules for each column so the supplemental value is the one used.
7. Process the sources and inspect a few products to confirm the final values.

Keep supplemental files narrow. A file that repeats every attribute from the primary source is harder to maintain and makes it unclear which source is responsible for a value. Practitioner tip: name each supplemental source after its job (“GTIN fixes”, “Ads exclusions”) so the next person understands it.

Common uses

Use	Columns in the supplemental source
Add GTINs your platform doesn’t store	id, gtin (plus brand and mpn where needed)
Improve titles for selected products	id, title
Exclude products from Shopping ads but keep free listings	id, excluded_destination
Add apparel attributes	id, color, size, age_group, gender
Assign shipping or return policy labels	id, shipping_label or return_policy_label
More frequent price and stock updates	id, price, availability (with Take latest)

Identifiers are one of the most common reasons to use a supplemental source. Only add values the manufacturer actually assigned; Google says not to make up or guess identifiers. See how to fix missing product identifiers. For titles, the rules in product titles for Google Shopping still apply.

Which source wins: attribute rules and Take latest

When the same attribute comes from more than one source, Merchant Center’s attribute rules decide the value. Google describes the default rule as taking the value from the supplemental or primary source. You can change that per attribute.

The Take latest operation uses whichever source updated the value most recently. Google uses it to replace the old “online inventory” data sources, which are deprecated: you now create a supplemental source with id, price and availability, linked with a Take latest rule. That lets you push price and stock updates more often than you regenerate the full primary feed.

1. Create a supplemental source containing id, price and availability.
2. Link it to the primary source.
3. In the primary source’s attribute rules, set price and availability to Take latest across the primary and supplemental sources.
4. Save as draft, test the rules on sample products, then apply.
5. Update the supplemental source whenever stock or prices change.

More on rules in product feed rules and attribute mapping.

Regional inventory data sources

If price or availability differs by region, Google has a separate regional inventory data source. Each row has id and region_id, and can include price, sale_price, sale_price_effective_date and availability for that region.

Landing pages for regional products still need to be crawlable: Google’s product page unavailable guide notes that with the regional availability add-on, URLs that include region_id must be crawlable. For selling into several countries rather than regions, see handling multiple countries and currencies.

Multi-client accounts

In a multi-client account (MCA), the parent account can define attribute rules and supplemental sources for its sub-accounts. That’s useful for agencies or brands with several stores that need the same fixes applied consistently. Note that an MCA also matters for website claims: Google’s URL verification guide says a URL can be claimed by only one account, and sub-accounts of an MCA inherit its claim.

Troubleshooting a supplemental source

1. Check the add-on is enabled and the source is linked to the right primary source.
2. Compare a sample of IDs character by character with Merchant Center’s product list.
3. Confirm the feed label matches the primary source.
4. Check the attribute rule for each column: is the supplemental value actually being used?
5. Reprocess or re-fetch the sources, then open a sample product to see the final value.
6. Check Products > Needs attention for new issues the changed values caused. See diagnosing data source errors.

When to get help

Supplemental sources are simple until several sources and rules overlap. If values aren’t applying, or you’re not sure which source is winning, our product feed optimization service can untangle the setup, and our Merchant Center service covers the wider account.

Frequently asked questions

Sources

• Google Merchant Center Help — Create a product data source
• Google Merchant Center Help — Set up your attribute rules
• Google Merchant Center Help — Feed labels
• Google Merchant Center Help — ID [id]
• Google Merchant Center Help — How to fix: Product page unavailable
• Google Merchant Center Help — About online store URL verification
• Google Merchant Center Help — Product data specification

Last reviewed October 10, 2026 against the official documentation listed above. Google changes Merchant Center features and policies regularly — always confirm details in your own account.