OptionKit lets you add option fields to your products so customers can personalize what they buy. Build text fields, dropdowns, checkboxes, color and image swatches, file uploads, and date pickers, then group them into reusable option sets assigned to products or collections. Premium options can add an upcharge — fixed, percentage, or per-character — carried through to the cart and checkout. Conditional logic shows or hides options, with per-language translations and per-market localization.