A primary feed is the main source of product data in Google Merchant Center: the file, spreadsheet or connection that creates your products and supplies their core details. Google now calls it a primary data source. Products can only be added through a primary source; every other kind of feed adjusts products that already exist.
How a primary feed works
The primary feed lists each product with its required attributes: an ID, title, description, link, image link, price, availability and condition, plus a GTIN and brand for most branded goods. Merchant Center reads it, checks it against the product data specification and either approves each item for Shopping ads and free listings or reports what is wrong.
There are several ways to supply one:
- A file in XML, CSV or TSV format, uploaded by hand or fetched on a schedule from a web address.
- A Google Sheet, which suits a small catalogue edited by hand.
- An API connection, usually built into a platform app such as the Google integrations for Shopify or WooCommerce.
- Products found automatically on your website, which Google can read from the structured data on product pages.
Each primary feed is set up for particular countries and a language, so a shop selling to British customers in pounds needs its products targeted at the United Kingdom and priced in GBP. A supplemental feed sits on top: it can add a custom label or correct a title, but it cannot create a product the primary feed does not contain.
Why it matters
Shopping ads have no keywords. Google decides which searches to show a product for largely from what the feed says, so the primary feed acts as your keyword list, your ad copy and your price tag at once. Weak titles, missing GTINs and vague categories limit where products can appear.
Errors carry a cost beyond reach. A price in the feed that does not match the price on the page, or stock shown as available when it has sold out, can get items disapproved, and repeated mismatches put the whole Merchant Center account at risk.
UK retailers have a few specific traps: consumer prices must include VAT, delivery costs must be set for UK addresses, and availability has to match what the product page says when Google checks it, which during a Boxing Day sale can change by the hour.
Common mistakes
- Running two primary feeds that contain the same product IDs, so items duplicate or overwrite each other.
- Fetching the feed once a day while prices change several times a day.
- Editing products by hand in Merchant Center, then losing the changes at the next scheduled fetch.
- Trusting a plug-in’s default mapping, which often sends the website’s page title rather than a proper product title.
- Ignoring the product issues report until sales from Shopping drop.
How to act on it
Choose one primary source per catalogue and per country, and treat it as the record everything else follows. If your shop platform produces the feed, fix data at the platform end so corrections survive the next refresh. Set the fetch frequency to match how often prices and stock change, and use supplemental feeds or feed rules for anything the platform cannot output.
Then review the product issues report every week, starting with disapproved and limited items that sell well. A clean primary feed is the foundation of the Performance Max and Shopping campaigns I run, and it supports your free listings in Google Shopping too.