Congklak

The problem

Congklak is a seed-sowing board game played across the archipelago under many names: dakon, congkak, sungka. The rules differ by region. Does the game end when a player has no legal move, or as soon as they have three empty holes? Does landing in an empty hole on your own side capture the opposite hole, or end your turn? Must a seed go all the way round the board before it can capture? Published sources disagree on all three.

Every congklak app I found picks one reading and presents it as "the rules". Two players who learned the game in different places can't tell whether the app is wrong or they are. I built this version for Indonesian players who want to recognise the game they grew up with, for newcomers who need to be taught, and for anyone curious where the rules come from.

What I built

You choose which region's rules to play

The app ships three rulesets, each tied to its sources. One follows the most widely used reading. One follows Sleman regency's cultural documentation, where the game ends at three empty holes. One follows Malaysia's national culture department, where you capture only after a full lap. The active ruleset is always named on screen. A comparison view replays the same moves under two rulesets side by side and marks the first move where they part ways.

Each source is weighed and recorded

The sources page lists five sources in three kinds: government cultural documentation, a specialist board-game reference, and a news article. Each carries a stated confidence. The Sleman source contradicts itself on when the game ends, so I recorded both readings and implemented the one it states most firmly. The news article reverses the capture rule compared with both other kinds. I logged it as a known disagreement and didn't implement it. I also turned down a fourth ruleset, because no source backed the differences it would have added.

Rules are data, so a new region needs no new code

Each ruleset is a data file with its options, sources and recorded disagreements. The game code never checks for a region by name. The build refuses to ship a ruleset without a citation. When the Malay lap rule needed something the format couldn't express, I extended the format and left the game logic untouched.

The 98 seeds are counted after every move

The board holds exactly 98 seeds. A sowing loop that loses or duplicates one is the classic bug in this family of games, and it's silent: play just continues, wrongly. I wrote a check that counts all 98 after every step of every turn, before I wrote the sowing itself. Because the rules engine always gives the same result from the same moves, undo, replays, the computer opponent and online play all build on it.

I tested the finished site by hand

The test suite covered the engine well, but it couldn't see the interface bugs. The computer opponent never moved at animated speeds. The three typefaces in the design were never loaded. The board shrank to 160 pixels wide on a phone. Also, the first version sowed anticlockwise, while all three sources say clockwise. I found each of these by using the built site in two browsers, and a layout test now pins the direction.

Result

Congklak is live and public, in Indonesian and English, and a ruleset without a citation fails the deploy. You can play a friend on the same device, the computer at three difficulty levels, or someone on another device by code with no game server. Seeds travel hole by hole with speed control, and a preview shows where a move will end before you make it. There is also a replay viewer and a learn mode with three board lessons. Traditional words such as lumbung, biji, menembak and dakon stay in the interface. I built it on 3 and 4 August 2026.