What a supplemental source does
A supplemental data source adds or updates attributes on products that already exist in your primary data source. It is matched to your products by ID. It cannot add or remove products, and it can't be used on its own.
Google used to call this a supplemental feed, and many guides still do. Feeds became data sources in Google Merchant Center, but it works the same way.
That makes it the safe place for improvements: better titles, product types, custom labels or missing attributes, while your Shopify app or feed tool keeps sending prices, stock and links.
When to use one
- Your feed comes from an app and edits made in Google Merchant Center are overwritten on the next fetch.
- You want a different title on Google from the one on your store page.
- You want to add custom labels, such as best seller or no sales, for campaign structure.
- A batch of products is missing an attribute, such as gender or age group, that the app doesn't send.
How to set one up
- In Google Merchant Center, go to Settings, then Add-ons, and turn on Advanced data source management. The supplemental sources tab only appears with it.
- Go to Settings, then Data sources, and open the Supplemental sources tab.
- Choose Add supplemental product data and pick a file, a Google Sheets template or the API.
- Use the exact product IDs from your primary source, and the same feed label and language.
- Choose which primary data source it should add to, then create it.
Keep it safe
IDs must match exactly, including any prefixes your Shopify app adds, or rows are ignored. Only send the attributes you mean to change. Avoid sending prices or availability from a supplemental source unless you keep them up to date, because an old price there will cause mismatches.
Attribute rules can control which source wins for each attribute if you need finer control.
How UltraROAS.ai does this for you
UltraROAS.ai creates and manages its own supplemental source in your Google Merchant Center. Titles, product types and labels it improves go there, matched to your exact offer IDs. Your main feed keeps ownership of prices, availability, links and identifiers, and if you cancel, the source is unlinked so your own feed takes over.