Free Tools Every Competitive Programmer Should Bookmark

If you've ever lost 20 minutes at 2 AM debugging a submask enumeration loop, or drawn a segment tree on paper for the fifth time this month, this post is for you. I want to share a collection of 31 free, browser-based tools built specifically for competitive programming — no signup, no installs, code stays client-side. They're grouped at Utility Tools Lab's Competitive Programming category , and they cover almost every "I wish there was a tool for this" moment from contest practice. Here's a tour of what's inside. Visualizing structures you normally only imagine Half the pain in CP isn't the algorithm — it's seeing what your data structure is actually doing. Graph Visualizer — paste a CP-style edge list and get a force-directed graph you can drag around. Toggle directed/undirected and 0/1-indexing, then copy the adjacency list back out. Segment Tree Builder — feed in an array, pick sum/min/max/gcd, and watch the tree render, plus grab a full C++ class template. Sparse Table Builder — visualizes every level of the O(1) RMQ precomputation, with live queries. Union-Find (DSU) Visualizer — watch path compression and union-by-rank happen live on a forest view. Path Finder — paint walls on a grid and run BFS to see the shortest path animate, then copy the grid as a C++ 2D vector. Sieve Visualizer — step through the Sieve of Eratosthenes on a color-coded grid. Sorting Visualizer and Binary Search Visualizer — step-by-step animations with live comparison counts, or lo/hi/mid tracking on your own array. These aren't just "nice to look at" — watching the not-found path in binary search, or the moment a submask loop wraps around, is often exactly where off-by-one bugs hide. Code generators that skip the boilerplate Some things in CP are conceptually simple but easy to typo under time pressure. These tools generate ready-to-paste C++: Bitmask Planner — set N ≤ 12, visualize all 2^N states and submask iteration order, get a DP skeleton. PBDS Generator — Order Statistics Tree boi