A LeetCode-style playground where your solution becomes a visual execution trace for trees, graphs, grids, linked structures, and nested maps. JavaScript and Python in the browser, replayable state changes, and optional timing stats for JS.
function invertTree(root) {
if (!root) return null;
const left = invertTree(root.left);
const right = invertTree(root.right);
root.left = right;
root.right = left;
return root;
}Replay how your data structures change. Understand and debug with a real execution trace.
JavaScript runs in a Web Worker; Python uses Pyodide in its own worker so the page stays responsive.
Play, pause, step, replay, and tune playback speed—including keyboard shortcuts.
Measure many runs with median, percentiles, and a chart. Benchmark mode is JS-only today.
Use the built-in editor with familiar patterns for each project category.
Tracked APIs turn structural work into a callstack of frames—no canned animation.
Step forward and backward, change speed, and inspect each operation in the log.
Play, pause, step, replay, and tune playback speed—including keyboard shortcuts.
Replay how your data structures change. Understand and debug with a real execution trace.
Open a curated playground to see the debugger on a real problem, or jump into the full browser.