Feed rules in Merchant Center let you modify product data from your feed without changing the source file. Rules are applied after your feed is fetched, transforming attribute values before they reach Google's index. This is useful when you cannot modify your CMS or feed source directly.
Append text to titles: add keywords or category labels to the end of product titles automatically. Extract values: pull product type or brand from another field if it is missing. Replace text: remove unwanted characters, promotional language, or formatting inconsistencies. Set static values: apply the same value to all products (useful for condition, availability, or age_group when all products share that attribute). Map values: translate your internal category names to Google's product_type taxonomy.
In Merchant Center Next, go to Products > Feeds, select your feed, then click the Feed rules tab. Click Add rule, select the attribute you want to modify, and choose the rule type. For text transformation, you can use set, append, find and replace, or extract from another attribute. Rules are evaluated in order -- you can chain multiple rules to the same attribute.
Title optimization: your feed has product names like "Blue Sneaker 42" but Google wants more context. A rule can append " | Brand Name | Footwear" to every title. Condition field: if your system exports condition as "new-arrival" instead of "new", a map rule can convert it. GTIN fallback: if GTIN is missing for some products, a rule can set identifier_exists to "no" automatically. Color and size: extract from product_type or title if dedicated fields are missing.
Rules cannot create entirely new data -- they can only transform existing values. Rules run after fetch but before indexing, so issues that prevent fetching (wrong URL, authentication failure) are not fixable with rules. Some attributes like price and availability cannot be safely transformed with rules -- changing these requires updating the source feed.