Cambio — an online card game

Cambio is a game of imperfect memory. You're dealt four cards face down, you get to peek at two of them once, and from then on you're guessing — swapping blind, spying with card powers, and racing to slap matching cards onto the pile. Lowest hand when someone calls "Cambio!" wins the round.

I wanted to play it with friends without installing anything, so I built it here.

Play Cambio →

How it plays

On your turn you draw a card — from the deck (only you see it) or the discard pile (everyone sees it) — then either keep it, swapping out one of your own cards blind, or discard it. Some cards have powers when you discard them fresh from the deck:

Card	Power
7, 8	peek at one of your own cards
9, 10	spy at one of an opponent's cards
J, Q	blind-swap any two cards on the table
K	look at one of yours + one opponent's, then optionally swap

At any moment — even when it isn't your turn — if you're holding a card that matches the rank on top of the discard, you can snap it down to shed it. Snap an opponent's card and you get to slide one of your own unwanted cards into their hand. Snap wrong and you draw a penalty card, so it's a real gamble.

When you think your hand is lowest, call Cambio. Everyone else gets one last turn, then all cards flip up and you score. Cards are worth their face value; aces are 1, face cards are 10, and black kings are −1 — the card you want. Play to 100; lowest total wins.

How it's built

The whole thing runs on the principle that the server is the only source of truth, because the entire game is about hidden information — a browser that knows the deck order has already broken the game. So the rules live in a single pure function that the server runs authoritatively; clients only ever receive a redacted view, and a card's identity is sent to you only when you've legitimately earned the right to see it. Bots run on the same code path as humans, so they can't peek either.

Play Cambio →