How Shuffled works

One verified shuffle per day. Here is exactly what happens when you press the button - and why every claim on this page is literally true.

1. The randomness

The deck is shuffled on the server, never in your browser - nothing about the order is decided on your device, so nothing can be tampered with there. Every random draw comes from Node's crypto module, the cryptographically secure random number generator that underpins TLS encryption and key generation. There is no seed, no timestamp trick, no pattern to predict.

2. The shuffle

We use the Fisher-Yates shuffle, walking the deck from the last card to the first. At each step, the current card swaps places with one chosen by crypto.randomInt, which uses rejection sampling so every position is chosen without bias. Fisher-Yates is mathematically proven to make all 52! possible arrangements precisely equal in probability - the gold standard for unbiased shuffling. A machine shuffle like this is actually more random than a human one: studies show a deck needs seven or more riffle shuffles before it approaches true randomness.

3. The fingerprint

The moment your deck exists, the server computes a SHA-256 hash of the exact card order - a digital fingerprint. Change even one card and the hash changes completely. Because the recipe is stated here, you can recompute it yourself and confirm the cards you see are the cards the server dealt. The shuffle and hashing code is public, verbatim, at github.com/PlayShuffled/shuffled-verification - run it yourself with Node.

4. The comparison

Your deck is then laid alongside every shuffle ever recorded here, one by one, position by position. A match means the same card in the same slot: if your 14th card is the Queen of Hearts and so is a stranger's, that is one match. Your result is the closest relative your shuffle has in the whole archive - and your shuffle stays in the archive, so a future stranger may match against it days or years from now.

5. Your tier

Your result is one number: how many of your 52 cards share a slot with your closest match. That number sets your tier, from Ghost up to Singularity, and its odds.

The odds describe a single pairing. Line up any two shuffles, card for card, and that is the chance they share that many positions. Seven in the same places is a roughly 1-in-13,700 event between two shuffles.

The odds of two decks sharing N positions

Between any two random decks, shared positions follow the fixed-point distribution: the expected number is exactly 1, and the chance of at least one is 63.2%. The per-pair odds for each exact count:

Note: The above represent the chances that any single pair of shuffled decks match at the indicated positions. The Shuffled database, however, compares each of your shuffles to every other shuffle we've recorded. This multiplies quickly - one thousand shuffles make nearly half a million possible pairings; one million make five hundred billion. This means that as the database grows, the likelihood of higher matches becomes greater and greater over time.

Everything else - one shuffle per day, accounts, what happens to your shuffle after today - is answered in the FAQ.