About Club Checkers

Club Checkers is a free checkers game that runs entirely in your web browser. It started life years earlier as a 3D game backed by a server, and was rebuilt from that original code so anyone can play it instantly.

Who makes it

Club Checkers is made by The Seasoned Programmer. For more, visit the YouTube channel The Seasoned Programmer (@theseasonedprogrammer).

Where it came from

The first Club Checkers was written in C#. A rules engine kept track of the board, generated the legal moves for every position and enforced compulsory captures, multi-jumps and crowning. Players saw the game in 3D, and every piece carried a permanent name, such as the red piece that started on a particular square, so the 3D client could animate exactly the right model when it moved.

The game itself lived on a server. Each move was sent through a message queue to a .NET service, which checked it, asked the computer player for a reply and stored the position in a database until the next request. Several computer players were written along the way: one that moved at random, one that always took the most pieces, and opponents that searched ahead using minimax with alpha-beta pruning.

Rebuilt for the browser

The current version keeps the same rules and the same way of naming pieces, but moves everything into the browser. The rules engine and computer opponent were rewritten in TypeScript, and the computer does its thinking in a background thread called a Web Worker, so the board stays responsive while it calculates. Nothing about your game is sent to a server: there are no accounts, and the game in progress is saved only on your own device.

The rewrite was also a chance to tighten up the rules and the computer player:

• Jumped pieces now stay on the board until the whole move is finished, as the official rules require, so a piece can never be jumped twice in one turn.
• A draw rule ends games where neither side can make progress, instead of letting two kings circle forever.
• The search was rewritten from scratch. It keeps calculating through capture sequences instead of stopping in the middle of an exchange, and the hardest level also judges position, not just the number of pieces.
• Moves animate hop by hop, and the board flips when you play White.

How the computer plays

The Medium, Hard and Expert levels use a negamax search with alpha-beta pruning. Starting from the current position, the computer tries each legal move, then each reply, and so on to a fixed depth: two moves for Medium, four for Hard and eight for Expert. It scores the positions it reaches and assumes both sides play their best. As pieces come off the board there are fewer moves to consider, so the search automatically looks further ahead in the endgame.

Medium and Hard count material, with a king worth a little over three ordinary pieces, the same weights the original game used. Expert also rewards advancing pawns, holding the center and keeping pieces on its back row to stop enemy kings, and it prefers to trade pieces when it is ahead. Easy doesn't search at all: it takes the biggest capture available, or otherwise picks a move at random.

Get in touch

Found a bug or have an idea for the game? Contact us. Or go back and play a game.