Widget is the interactive part of a WIDGET problem: a self-contained web page, uploaded as a bundle, which the participant solves the problem in. The page is shown in a sandboxed frame under the statement, and it talks to the page around it over the widget protocol: the host asks it for the answer to submit, and hands an answer back to it to show what a submission contained. The answer is a JSON document of the widget's own design; the platform stores and grades it without reading inside.

The bundle follows the problem's versions the way tests and statements do, so a submission made against an earlier version is shown in the widget it was made with.