Many Web applications do not meet the precise needs of their users. Browser extensions offer a way to customize web applications, but most people do not have the programming skills to implement their own extensions.

In this paper, we present spreadsheet-driven customization, a technique that enables end users to customize software without doing any traditional programming. The idea is to augment an application’s UI with a spreadsheet that is synchronized with the application’s data. When the user manipulates the spreadsheet, the underlying data is modified and the changes are propagated to the UI, and vice versa.

We have implemented this technique in a prototype browser extension called Wildcard. Through concrete examples, we demonstrate that Wildcard can support useful customizations—ranging from sorting lists of search results to showing related data from web APIs—on top of existing websites. We also present the design principles underlying our prototype.

Customization can lead to dramatically better experiences with software. We think that spreadsheet-driven customization offers a promising new approach to unlocking this benefit for all users, not just programmers.

This paper is best viewed in the online version (https://www.geoffreylitt.com/wildcard/salon2020), which includes videos demonstrating the interface.