You understood the solution. You wrote the code. But it's WA — off-by-one, null pointer, wrong boundary. Paste your code and see exactly which line breaks and why. Stop guessing. Watch every variable, every pointer, every step.
Find My BugIs it <= or <? Step through your binary search and see exactly when the pointer overshoots. No more guessing — see the boundary condition fail in real time.
Your linked list traversal crashes on node.next but node is None. Watch head, curr, slow, fast pointers move through the list and spot the exact step where the null dereference happens.
Wrong answer? Runtime error? One click and AI highlights the exact line, explains why i+1 should be i, and suggests the fix. Spend time grinding, not stuck on one problem.
TraceLit is the first visual algorithm tracer for technical interview preparation. You paste your own Python code, enter test cases, and step through execution line by line while watching linked lists, trees, and other data structures transform in real time.
Paste your Python code and a test case. TraceLit executes your code step by step, capturing every variable and data structure at each line. You step forward and backward through the trace, watching pointers move and nodes update in an interactive visualization.
TraceLit currently supports Python. It accepts standard LeetCode-style function signatures and input formats such as [1,2,3,4,5] for linked lists and [1,null,2,3] for binary trees.
Yes. TraceLit is completely free to use during the beta period. No sign-up or installation is required — just open the web app and start tracing.
Unlike Python Tutor, TraceLit renders linked lists and trees as interactive visual graphs instead of memory diagrams. Unlike VisuAlgo, TraceLit runs your own code rather than pre-built algorithm animations. TraceLit is purpose-built for coding interview prep with data structure visualization and AI-powered debugging.
TraceLit visualizes linked lists (ListNode) and binary trees (TreeNode) as interactive graphs with pointer tracking (head, curr, prev, slow, fast). It also displays arrays, hash maps, and all primitive variable types in a step-by-step locals table.
TraceLit is in beta and we're building it around you. Bug reports, feature requests, or just a quick thought — please share it. Your feedback directly shapes what we ship next.
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