A site plugin is a custom element that renders in a slot on a widget built by a Wix business solution, such as the Wix eCommerce Checkout page. This reference is the contract for a plugin you add as an extension: the generated files, the configuration object, the custom element that renders in the slot, and the plugin's settings panel.
The file set and configuration object are the same whether you add the plugin in a Studio Two site project or in a Wix CLI app.
extensions.sitePlugin() configuration fields, the custom element and the slot data it receives, and the settings panel.The configuration file lists the slots the plugin can fill. For the widgets that have slots, each slot's placements values, and the data each slot passes to a plugin, see About Slots.
The configuration file's placements field takes the appDefinitionId, widgetId, and slotId values that each widget's page lists for its slots.
Note: The screenshots and slot locations in About Slots and its widget pages might not match every Wix editor. In some editors, a widget and its slots might look different, or not exist.
Last updated: 2 November 2026