How to override Google's automatic product category with a supplemental feed

What an override actually does

Start here, because the usual framing is wrong. Google’s documentation says the attribute can be used to override Google’s automatic categorization in specific cases, and the page names them: enforcement of category-specific attribute requirements, targeting of Google Ads campaigns, and alcohol. Nothing on that page says a merchant-submitted value is always preferred.

So the honest expectation is this. Submitting a category reliably determines which category-specific attribute rules apply to your feed and what you can target in Google Ads. It is not a mechanism for correcting how Google classifies your product in every surface, and a guide that promises that is promising something Google does not document.

That still leaves a real job. If your products are sitting in a category whose attribute requirements do not match what you sell, or you need to build Shopping product groups by category, the value has to be in the feed — and a supplemental feed is how you get it there without rebuilding your primary source.

A supplemental feed cannot add products. It can only add attributes to products Google already has.

What a supplemental data source can and cannot do

A supplemental data source adds or overrides attributes on products that already exist in a primary source. Google is explicit about the boundary: it can’t be used to add or remove products or be used as a standalone data source.

It matches on id. Google’s documentation says your product data will only be updated when the supplemental product data sources contain IDs that are in a primary product data source, and asks you to match your Product ID from your product data source exactly. Two further things have to line up as well: the data source label (feed label) and the language. A supplemental feed that silently does nothing is almost always one of those three not matching.

Attributes Google documents as things a supplemental source can handle include overriding the title, adding custom labels, adding GTINs and adding local inventory data. google_product_category is an optional product attribute and supplemental sources are described as carrying required or optional product attributes… missing from your primary data source, which is the general capability this relies on. We have not found a Google page that names this specific attribute in a supplemental context, so treat it as the general case rather than a documented guarantee, and verify against your own feed once it is running.

First: turn on the add-on, or you will not find the tab

This is the step that wastes the most time. The Supplemental sources tab only appears once the Advanced data source management add-on is enabled. Until then you can read every guide correctly and still not see the option.

In Merchant Center: Settings → Add-ons → enable Advanced data source management.

Building the feed

1. Go to Settings → Data sources and open the Supplemental sources tab.
2. Choose Add supplemental product data and pick how it will arrive: a file upload, a Google Sheet, or the API. A Google Sheet is the easiest to iterate on.
3. Fill in the file name, then the fields that make the join work: Product ID, data source label and language. These must match the primary source exactly.
4. Select the primary data source this supplements, then Create data source.
5. The file itself needs two columns and no more: id and google_product_category. Extra columns are extra things to get wrong.

Put the numeric ID in the category column rather than the path. Google accepts either but recommends the ID, and an ID cannot be broken by a rename or a mistyped ampersand.

Generating the file for a real catalog

Two columns for five thousand products is still five thousand category decisions. Our Bulk Category Mapper writes exactly this file: upload your catalog with its id column, and one of the outputs is a two-column supplemental-feed.csv containing only the rows confident enough to submit without review. The rows it was not sure about go into a separate file with their runner-up categories, so you check a short list instead of the whole catalog.

The split matters here more than usual. A supplemental feed is applied without anyone reading it, so the bar for “good enough to include” should be higher than the bar for “probably right”.

Check that it landed

After processing, open a product in Merchant Center and look at its category. If nothing changed, work through the join in order: does the id match character for character, is the data source label the same, is the language the same? Those three account for nearly every silent failure.

If the value was accepted but a category-specific attribute is now being demanded that you were not expecting — an apparel size or colour, say — that is the override working as documented. Those requirements follow the category.