I built a browser number strategy game where arithmetic becomes board control

love mars Posted on May 31 I built a browser number strategy game where arithmetic becomes board control # gamedev # javascript # showdev # sideprojects The idea Most math games feel like timed quizzes: answer fast, move on, repeat. I wanted to build something with a different texture. In Number Duel , arithmetic is not the homework you do before the fun starts. It is the move system. You pick numbers to shape the board, limit your opponent, and set up future threats. The math is simple enough to play immediately, but the choices start to feel surprisingly tactical. How it works Each player has an active number from 0 to 9. On a turn, the two active numbers combine to create a target. You claim the matching cell on a 5x5 board. Connect four cells in a row to win. For example, in Sum Duel : I pick 9 You pick 3 The target becomes 12 The player whose turn it is can claim a 12 cell The interesting part is that your number does not only create your own move. It also controls what your opponent can do next. That shared constraint is where the strategy lives. Three modes are live Sum Duel is the most approachable mode. Active numbers are added together, so the board is easy to read and the tactics are about timing, blocking, and forcing useful totals. Product Duel makes the board spikier. Multiplication creates repeated targets, unreachable zones, and more dramatic tempo swings. Fifteen Duel is a smaller puzzle mode using the numbers 1-9. First to claim three numbers that sum to 15 wins. The hidden trick: the eight winning triples are exactly the rows, columns, and diagonals of the 3x3 magic square, so the mode is secretly tic-tac-toe in disguise. The hardest problem was onboarding The game logic was not the hard part. The hard part was getting the rules to click before a new player bounced. I tried to make the first screen do most of the teaching: Put the board front and center Highlight legal cells so players do not need to calculate every option Keep the first match sho