Google Merchant Center Supplemental Feed Guide

What a Supplemental Feed Is

A supplemental feed is a secondary data source that provides additional or replacement attribute values for products already in your primary feed. It cannot add new products; those must come from the primary feed. What it can do is override or supplement attributes: add missing fields, correct values, or add custom labels without touching your original data source.

Common Use Cases

Adding custom labels: your primary feed may not have campaign segmentation data. A supplemental feed can add custom_label_0 through custom_label_4 values based on your own categorization (margin tier, clearance status, seasonal relevance) without requiring a database change to your primary feed. Fixing attribute errors: if your primary feed has systematic errors (wrong condition values, missing GTINs, incorrect availability) and you cannot modify the source quickly, a supplemental feed can override those values while you fix the underlying issue. Adding promotional data: sale_price and sale_price_effective_date can be managed through a supplemental feed that gets updated during promotional periods without modifying the entire product catalog.

How Supplemental Feeds Are Matched

The matching key is the product's item_id (or id attribute). For each item_id in the supplemental feed, Merchant Center looks for the corresponding product in the primary feed and applies the supplemental data. If an item_id in your supplemental feed does not match any product in the primary feed, the supplemental data is ignored. Ensure your supplemental feed uses the same item_id format as your primary feed.

Setting Up a Supplemental Feed

In Merchant Center, navigate to Products then Feeds. Click the plus button to add a new feed. Select "Supplemental feed" as the feed type. Choose your upload method (Google Sheets, file upload, or URL fetch) and configure it. Under "Linked primary feeds," select which primary feed this supplemental feed should apply to. You can link one supplemental feed to multiple primary feeds if they share the same item_id format.