Creating a Supplemental Data Source in Google Merchant Center

A supplemental data source, also known as a supplemental feed, is used in Google Merchant Center to enrich or update the product information already provided by your primary feed. It helps fill in missing attributes, refine existing details, or enhance product data for better advertising performance. Unlike a primary feed, a supplemental feed cannot be used to create or remove products; it can only modify information for items that already exist in your primary feed.

This article explains how supplemental data sources work and guides you through the steps to create and configure one in your Merchant Center account.

Introduction to Supplemental Data Sources 

A supplemental data source (supplemental feed) allows you to provide additional or updated product information for items already in Google Merchant Center. For example, you can add custom_label, refine title, or supply missing attributes such as gtin. A supplemental source cannot function on its own—you must have a primary data source uploaded and approved for it to work. For details on how primary and supplemental data sources interact, refer to Google’s official guide: "Create a product data source."

In multi-client accounts (MCA) or sub-accounts, you can create supplemental data sources at different levels within the account structure. Ensure that each supplemental source is linked to the correct primary data source (with the same country/language target) so updates apply properly. For more information, refer to Google’s guide: "Set up supplemental product data sources for multi-client accounts."

How to Create a Supplemental Data Source

Follow these steps to create and configure a supplemental data source:

1. log in to your Google Merchant Center account.

2. Navigate to Settings > Data sources > Product sources > Supplemental sources, then click Add supplemental product data to begin creating a supplemental data source.

   Note: If you are setting up supplemental sources for the first time, go to Settings > Add-ons and click Activate next to Advanced data source management to enable the add-on first.

   

3. Select your preferred method to upload product data, provide the required files or information, and click Continue.

   

   • Add product data from a file: Upload a file manually, via SFTP, Google Cloud Storage, or your computer.
   • Use Google Sheets (Recommended): Use a generated template or choose an existing Google Sheet. This method is simple to set up, easy to maintain and update, and suitable for most merchants. For more details, refer to Google’s official guide: "Add products to Merchant Center using Google Sheets."

   • Add product data using API: Use the Merchant API if you manage feeds programmatically. For more information, refer to Google’s official guide: "Overview of Merchant API."

     Note: When using the Merchant API, supplemental source updates support partial changes and do not reset the product’s 30-day expiration timer. To refresh the expiration date and prevent products from expiring, you must submit a full product insert or update through your primary data source.

4. Follow the on-screen prompts and enter the required information, which may vary depending on the upload method:
   • File name: Enter the name of the file you will submit (if applicable). It should exactly match the file name and include a valid extension.
   • Product ID (id): Make sure the ID values in your supplemental data source are identical to the IDs in your primary feed so Google can match and apply the updates correctly.
   • Data source label: A label used to help categorize and identify this data source in campaigns (only uppercase letters, digits, hyphen, or underscore).
   • Language: The language used in your product data. Learn more about Supported languages and currencies.

5. Select the primary data source you want this supplemental data to update, then click Create data source.

   

6. Once created, you can view and manage your supplemental data source under the Supplemental sources tab.

   

7. Verify processing and results: 

   • After the first upload or fetch, go to Products > Needs attention in your Merchant Center to check for any errors.

     

   • Confirm that the updated attributes (e.g., titles, labels, custom attributes) are correctly applied to the existing products.

Best Practices and Tips

A supplemental data source is a powerful optimization tool, but it should be used strategically. Follow the guidelines below to maintain data accuracy and prevent product disapprovals.

Strict Data Matching is Required

• ID Consistency: Ensure that the id values in your supplemental source exactly match the IDs in your primary feed. Matching is case-sensitive and must include all prefixes or suffixes. Without an exact match, updates will not be applied.

Use for Enrichment and Overrides Only

• Avoid Over-Reliance: Supplemental sources are intended for enrichment (e.g., adding custom_label) or overriding specific attributes such as title or sale_price.
• Not a Replacement: A supplemental source should not replace your main product data file. Your primary feed must always contain a complete set of required product attributes.

Maintain Data Quality and Compliance

• Follow Specifications: All attributes included in the supplemental source must follow Google’s product data specification. Use valid attribute names, correct formatting, and the same language as your primary feed.
• Monitor Diagnostics: After each update, check the Needs attention tab to verify that your intended changes applied successfully and that no new issues were introduced.

Know the Limitations

• Primary Feed Is the Source of Truth: If you plan large-scale updates, such as a full pricing revision or major structural changes, you should update the primary feed directly.
• Expiration Resets: Some issues, such as the item expired status that appears when a product has not received a full update in 30 days, cannot be resolved with supplemental source updates. To reset the expiration timer, you must submit a full product insert or update through your primary data source.