Chess999.com
A chess platform where you can play with friends online, challenge an AI, practice openings and endgames, analyze moves with Stockfish, and explore profiles of top players from Lichess and Chess.com.
The Problem
Chess999 was built to bring together the things chess players actually want in one place — casual games with friends, AI practice, move analysis, and access to top player data — without needing to jump between different tools and platforms.
What We Built
I worked on this alongside a co-developer. The stack is Next.js and we built on top of well-established chess libraries rather than reinventing the wheel.
Online play — Players can create a private room to play with friends or open a public room for anyone to join. You can also see how many players are actively playing at any given time. Real-time move syncing is handled through polling.
AI opponent — Play against an AI powered by Stockfish, which also drives the move analysis — showing scores for possible moves, explaining decisions, and suggesting better lines.
Practice mode — Users can work through openings, endgames, and other motifs to sharpen specific parts of their game.
Game analysis — In practice mode, Stockfish runs alongside the game in real time — showing the winning probability for each move as you play so you can learn and adjust on the spot.
Player profiles — Browse profiles and stats of popular players pulled from Lichess and Chess.com via their public APIs.
Board customization — Change board and piece themes, and view full play history.
Technical Challenges
The focus was on integrating existing tools well rather than building from scratch. Wiring up Stockfish for live analysis, connecting the Lichess and Chess.com APIs, and keeping online games in sync through polling were the main moving parts to get right.
Results & Impact
Chess999 is live at chess999.com. It’s a company project with no public source code.