Mister Nester is an interactive console for learning and experimenting with data nesting in d3.js. The interface presents a text area where tabular data—such as county-level population and Hispanic percentage by year—can be pasted, and a preview pane displays the nested structure generated from it. The visualization updates in real time as the input is edited, using the d3.v3 library to parse and reorganize the data into a hierarchical format. Users can select from sample datasets and trigger the nesting process via a button, making the tool a practical playground for understanding how d3 handles nested data relationships.