Google Shopping Supplemental Feeds: How to Fix and Enrich Your Product Data

For Shopping and Performance Max, the quality of your product data determines how often your products show up, and which searches they show up for.

The problem is that you often can’t get at individual fields easily. Your ecommerce platform fills some attributes automatically, or won’t let you edit them at all. A supplemental feed lets you adjust that data after the fact, without rebuilding your entire feed.

In this post, I’ll walk through what a supplemental feed does, how to set one up, and when it’s worth the effort.

What is a supplemental feed?

A supplemental feed is a second data source that you set up in Merchant Center alongside your primary feed. It adds to or overrides individual attributes on products that are already in your account from the primary feed.

The two are linked by the id. For each id in the supplemental feed, Google checks whether the product exists in the primary feed, then pulls in the values from the supplemental feed. If you provide a title for id ABC123, that title replaces the one from the primary feed. Every other attribute on that product stays the same.

One limit to know up front: a supplemental feed can’t create new products. It only works on ids that already exist.

Why supplemental feeds? What do you actually need them for?

To see the point of a supplemental feed, it helps to look at feed management tools first. Tools like Channable, DataFeedWatch, and Feedonomics pull your product data out of your shop, transform it with rules, and push the result into Merchant Center as your primary feed.

When you’re running a tool like that, you make most of your edits right there.

A supplemental feed works one step downstream. It sits on top of the feed that’s already in Merchant Center and corrects or adds individual attributes.

That’s the right move whenever you can’t get at certain fields any other way, or you just need a quick fix without touching your whole feed setup.

Here are the cases that come up most often:

• Standardize or optimize titles: roll out a consistent brand + model + variant structure across your whole catalog.
• Fill in missing attributes: add GTIN, product_highlights, material, or color for products where they’re missing in the primary feed.
• Assign custom labels: tag products by static categories like brand, product category, or margin, so you can build your campaigns and asset groups around them.
• Add sale prices and promotions: surface sale prices or promotion flags.
• Fix disapproved products: correct the products Google rejected, without touching the primary feed.
• Make bulk changes: update many products at once instead of editing each row by hand in your shop.

You can attach several supplemental feeds at once, one per job: one for custom labels, another for title overrides, a third for missing GTINs.

That keeps each data source clean and makes it obvious which feed controls which attribute.

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How do you set up a supplemental feed?

To set one up, you need two things: a data source with your new values, and the connection in Merchant Center. The data source always has an id column plus the attributes you want to add or override.

You’ve got a few options for the data source:

• Google Sheet: the most flexible option for manual overrides. You edit the values right in the sheet, and Merchant Center syncs them on a schedule. For most shops, this is the best place to start.
• Scheduled URL fetch: handy when another system already outputs the extra data as a file and you want to pull it in on a regular schedule.
• File upload: good for one-off or occasional fixes.
• Content API: for large, automated setups with a custom integration.

Here’s how you create the supplemental feed in Merchant Center Next:

1. Under Settings, open Add-ons and turn on “Advanced Data Source Management.” That’s what unlocks supplemental sources in the first place.
2. Under Data sources, next to “Primary sources,” open the “Supplemental sources” section.
3. Click “Add supplemental product data” and connect your source (Google Sheet, file, URL, or API).
4. Name the columns to match the official attribute names exactly, starting with the id column.
5. Link the supplemental feed to the right primary feed and target country.

Once it’s connected, the values kick in on the next fetch. The most common thing that trips people up here is the id match.

Not every attribute belongs in a supplemental feed. Stable, descriptive fields are a good fit: title, description, product_highlights, gtin, material, or color.

Be careful with volatile attributes like price and availability. Those change often and have to match your shop and landing page at all times. A supplemental feed you maintain by hand goes stale fast here and creates price mismatches that get products disapproved.

Custom labels are worth a second look. Static groupings like brand, product category, or margin work well. Labels that shift dynamically with performance or price change constantly, so they belong at your automatic feed source.

When is a supplemental feed worth it?

A supplemental feed is the best fit for a smaller catalog that doesn’t change all the time. When your products and their ids stay put over the long run, your overrides stick, and you only touch them when something actually changes.

In that setup, there’s a lot you can do:

• sharpen your titles and make them consistent across the catalog
• set custom labels for static categories and build your campaigns around them
• fill in missing attributes like product_highlights or material

Shopify is an especially handy example. When you use the Shopify Google app, it pushes your product data into Merchant Center automatically, but it only gives you limited control over individual field values. With a supplemental feed, you can override titles, custom labels, or missing attributes through a Google Sheet without leaving the app. The same goes for any setup where you don’t have a solid plugin or tool to enrich your product data.

It’s a different story with a large catalog that changes constantly. When products are always coming and going, maintaining a supplemental feed by hand gets hard to keep up with. In that case, go with a feed management tool like Channable. It pulls your product data from the shop automatically, enriches it with rules, and keeps it current.

The enrichment happens right at the source and scales with your catalog.

Building a supplemental feed with AI

When it comes to filling in all those attributes, there’s a faster way now. AI tools like Claude are great at prepping a Google Sheet as a supplemental feed, because this kind of structured, spreadsheet-heavy work is right in their wheelhouse.

The approach is simple: hand the model the relevant Merchant Center documentation, the guidelines for titles and attributes, and your own best practices. From there, Claude or another AI tool gives you policy-compliant output you can drop straight into the sheet.

This pays off more than you’d think. Most shops fill in only a handful of required attributes and leave a lot of useful fields empty: product_highlights, material, color, or size. Every attribute you fill gives Google more context about which searches your product fits. That’s exactly the kind of repetitive work across hundreds of products that AI can take off your plate.

AI clearly has more to offer here, especially for enriching large catalogs. But even now, the basic recipe already works: a well-briefed model, a ready Google Sheet, and a connected supplemental feed.

FAQ: Common questions about supplemental feeds

Conclusion

A supplemental feed is your tool for fine-tuning product data without rebuilding the primary feed. It’s strongest with a stable catalog, and anywhere your ecommerce platform or feed tool can’t get at certain fields.

To get started, you need a Google Sheet with the correct ids and attribute names, the right connection in Merchant Center, and a sense for which fields are stable enough to maintain there. For the actual filling-in, it’s worth trying AI tools, since they can take a big chunk of that per-product work off your plate.

Thanks for reading this far. Good luck cleaning up your product data and your Shopping campaigns.

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