Themes and front-end
Metafields
Metafields are custom fields added to a Shopify object — product, variant, customer, order, company — to store data the platform does not ship with. They are typed and validated, and they are readable from the theme in Liquid, from the API, and from inside a Shopify Function.
Also called: metafield, custom fields, custom data
This is the first tool to reach for when a piece of data appears that Shopify does not have: a variant’s case pack, a product’s technical sheet, a customer code from the ERP. Before installing an app or inventing a convention inside tags, the answer is almost always a metafield.
Typed, and that matters
A metafield is not free text: it has a type (integer, decimal, date, product reference, file, list) and Shopify validates what goes in. That avoids the classic of reading "6 pcs" where the code expected 6.
And the type decides how it reads in the theme. A product reference arrives as the product object, not as an ID you have to resolve by hand.
Variant versus product
The decision people get wrong most often. If the data changes by size or colour, it belongs on the variant. The case pack is a clear example: not every size ships in boxes of 6. A product-level metafield forces an approximation, and the approximation shows up in the warehouse.
Why they matter to Functions
A Shopify Function cannot call anything: all it sees is what its input query hands it. So any business rule that depends on your own data needs that data in a metafield, with its alias in the query. If the data lives in an app or in an external system, the Function cannot use it.
Documentation: metafields.