You’ve found a problem in your product data. Maybe the titles need a keyword, a batch of products is missing GTINs or you want to tag your best sellers with a custom label. Your main feed may come straight from your store platform and you’d rather not touch it. This guide is for store owners and feed managers who want to use a supplemental feed in Google Merchant Center to patch product data on top of the primary feed. By the end you’ll know what it can and can’t do, how to add one and how it matches your products.
A supplemental feed (Google now calls it a supplemental data source) is a secondary source that adds details to, or updates details on, products that already exist in your primary source[1]. You turn on the Advanced data source management add-on, add a supplemental source under Data sources, link it to your primary source and match rows using the product ID[1].
Good to know
Google’s current wording is “supplemental data source”, and its glossary entry for “Data source” says it was previously known as “Feeds”[5]. Older guides still say “feed” and mean the same thing. If you need the basics first, read the beginner’s guide at https://oxfordimpulse.com/beginners-guide-google-merchant-center-feed/ and then come back.
What a supplemental feed can and can’t do
Think of it as a patch. Google defines it as “a secondary data source used to provide more details or update existing details”[1]. The primary source stays in charge of which products exist. The supplemental source only adds to them or updates their details.
Google’s own use cases include[1]:
- Custom labels
- Promotion IDs
- Titles
- Excluded destination
- Missing GTINs
- Local inventory
These are examples, not a complete list of what a supplemental source can change, so test with a small file first and check the result.
Here’s what it can’t do. It can’t add products. It can’t remove products. It can’t work as a standalone source. Only primary data sources add or remove products[1]. If you upload a row for a product ID that doesn’t exist in the primary source, there is nothing for it to patch.
Watch out
A supplemental source is not the same as attribute rules. Attribute rules transform data inside a primary source, on its Attribute rules tab[2]. A supplemental feed supplies your own values from a separate file or sheet. Rules suit pattern-based changes across many products. A supplemental feed suits product-by-product values you’ve decided yourself.
Step 1: Turn on Advanced data source management
If you can’t find the Supplemental sources tab, check this first. The tab only shows when the “Advanced data source management” add-on is on[1].
- Open Merchant Center and click the Settings (gear) icon.
- Choose Add-ons.
- Find Advanced data source management and turn it on.
Step 2: Check your primary source and product IDs
Diagnose before you build anything. A supplemental source is only as good as its match to the primary one, so spend a few minutes on this.
- Go to Settings (gear) > Data sources and open your primary source.
- Look at the product IDs. These are the id values in the feed. Write down the exact format, including capitals, dashes and any prefixes.
- Note the Feed Label and the language of the primary source.
Matching works through the ID. The ID in your supplemental file has to match a product in the primary source, and the Feed Label must exactly match the primary source’s label[1]. The match has to be exact, so copy the value as it appears.
If your patch is about GTINs, see https://oxfordimpulse.com/what-is-gtin-google-merchant-center/ for a plain explanation of what a GTIN is.
Step 3: Prepare your supplemental file
Google lets you choose from three input types: a file, a Google Sheets template or an API[1]. A Google Sheet can be easy to maintain, because a teammate can edit it without touching code.
A simple layout keeps the file easy to check:
- One column for the product ID.
- One column for each attribute you want to change, using Google’s attribute names, such as title, gtin or custom_label_0.
- One row per product you want to patch. Leave out products you don’t want to change.
Tip
Build your first file with five products, not 5,000. If the patch works, add more products. If it doesn’t, you have only five rows to debug.
Also decide what each row should do. A value in a cell adds that detail or updates the existing one[1].
Step 4: Add the supplemental data source
Now create it. These are the on-screen steps from Google’s help documentation[1].
- Click the Settings (gear) icon, then Data sources.
- Open the Supplemental sources tab.
- Click Add supplemental product data.
- Choose an input type: file, Google Sheets or API. Click Continue.
- Enter the file name, the Product ID, the data source label and the language.
- Select the primary data source you want to link it to.
- Click Create data source.
Don’t skip the linking step. You select the primary data source to link the supplemental source to, so make sure you pick the right one[1]. If your products show no change, check the link first.
A note on custom matching
By default you match on the ID[1]. Google also offers custom data source matching on an attribute other than the ID, but it’s limited to some merchants and capped at 30,000 rows[3]. If you don’t see the option, match on the ID.
Step 5: Check that the patch worked
Don’t assume. After the first upload, check it.
- Open the supplemental source and look for any errors or warnings.
- Go to Products in Merchant Center and open two or three of the patched products. Check that the new value is showing.
- Compare against the landing page. A patched title or GTIN should still agree with what’s on the product page, or you’ll create a new problem.
Be patient, too. Changes may not show straight away, so check again later before you assume it failed.
Step 6: Keep it updated and within limits
A patch is not a one-off if your data changes. If you’ve set custom labels from a sheet, someone has to own that sheet.
Know the quotas. Google allows up to 200 data sources per standalone account or sub-account, and uploads are capped at 500 per day for supplemental sources versus 100 per day for primary sources[4]. That leaves room, but it matters if you automate updates every few minutes through the API. Batch your changes instead.
Fix the cause where you can. If the same product keeps needing the same patch, ask whether the real fix belongs in your store platform or in the primary feed. A supplemental feed is the right tool for data your platform can’t hold. It’s the wrong tool for covering up a permanent error you could fix at the source.
Common mistakes and how to avoid them
- Mismatched IDs. Copy the IDs from the primary source instead of retyping them. Watch for leading zeros that spreadsheets strip.
- Wrong Feed Label. It has to match the primary source exactly[1].
- Expecting new products to appear. They won’t. Add them to the primary source[1].
- Forgetting to link the primary source. Check the link first when nothing changes[1].
- Using it instead of attribute rules. If you need a pattern-based change across many products, consider attribute rules[2].
- Patching data that disagrees with the page. Prices, availability and titles should reflect what a shopper sees.
Supplemental feed checklist
Once your first patch is live, check the Products list again later, then decide which fixes belong in the primary feed for good. For the wider picture of how your setup fits together, read https://oxfordimpulse.com/google-merchant-center/ and, if you’d like help reviewing your feed, Oxford Impulse can take a look.
FAQs
What is a supplemental feed in Google Merchant Center?
Why can’t you see the supplemental sources tab?
The tab only appears when the Advanced data source management add-on is on. Go to Settings (gear) > Add-ons and switch it on[1].
Can a supplemental feed add new products?
No. Only primary data sources add or remove products, and a supplemental source can’t work as a standalone source[1]. Add new products to the primary source first.
How does a supplemental feed match your products?
It matches by ID. The ID in your supplemental file must match a product in the primary source, and the Feed Label must exactly match the primary source[1].
Can you match on something other than the ID?
Custom matching on a non-ID attribute exists, but it’s limited to some merchants and capped at 30,000 rows[3]. If you don’t see it in your account, use the ID.
How do you add a supplemental data source?
Go to Settings (gear) > Data sources > Supplemental sources tab and click Add supplemental product data. Choose the input type, fill in the file name, Product ID, label and language, pick the primary source and click Create data source[1].
What input types can you use?
You can use a file, a Google Sheets template or the API[1]. A Google Sheet can be easy for small teams to maintain because a teammate can edit it without touching code.
How do you override product data in Merchant Center without editing your main feed?
What’s the difference between a supplemental feed and attribute rules?
Attribute rules transform data inside a primary source from its Attribute rules tab[2]. A supplemental feed brings in separate values you supply yourself. Use rules for patterns and a supplemental feed for product-specific values.
Are there limits on supplemental uploads?
Yes. Uploads are capped at 500 per day for supplemental sources, compared with 100 per day for primary sources[4]. Batch your changes rather than uploading constantly.
Sources
- Google Merchant Center Help: Create a product data source support.google.com
- Google Merchant Center Help: Set up your attribute rules support.google.com
- Google Merchant Center Help: Set up custom data source matching support.google.com
- Google Merchant Center Help: Understanding quotas in Google Merchant Center support.google.com
- Google Merchant Center Help: Data source (previously known as Feeds) support.google.com
