Stencil is BigCommerce’s integrated theme engine for storefronts hosted directly by BigCommerce. The visual presentation and client-side functionality of a Stencil storefront is controlled by a theme package that is uploaded or obtained from the theme marketplace.
For developers familiar with traditional server-side frameworks and common HTML template patterns that comprise their view layers, Stencil likely has a lower barrier to entry compared with a fully composable solution. The trade-off is more limited flexibility for customization of server-side functionality.
The officially maintained, open-source Cornerstone theme is an optimized, responsive, and fully functional starting point for your custom theme development. Cornerstone is the default theme applied on every new Stencil storefront.
The following technologies are key parts of the existing tech stack in Stencil and the default Cornerstone theme, or else key tools for common customizations.
Developers have full freedom to customize the dependencies and libraries loaded within their Stencil package, as well as to inject JavaScript for complex features. This means that most custom features can be achieved, as long as a client-side strategy is feasible. However, due to the nature of Stencil as an integrated theme engine, customization affecting server-side behavior is more limited.
The BigCommerce Page Builder is a visual editor available in the store control panel that allows admin users to build and format content throughout the storefront without the need for changing theme files or writing code.

Page Builder provides two key features to customize your store’s content:
Page Builder is the visual editor solution specifically for Stencil themes. Your own theme supports the editing interface by defining and applying customizable settings, as well as defining the regions in which widgets can be used.