Is the deck fair?

Every hand you play on your own is shuffled before the first card and locked, so you can check afterwards that you were dealt from the deck that was fixed at the start. Here is how it works, how to check a hand yourself, and every test from millions of deals.

How a hand is dealt

1. Before the hand, your device draws a secret key: 32 random bytes from its secure random source (iOS's on an iPhone, Web Crypto in a browser).
2. Before any card is dealt, the app writes down the key's fingerprint: its SHA-256 hash. A hash can't be worked backwards to the key, and no other key gives the same one.
3. The deck is built from the key alone, with the published method below. The same key always gives the same deck, card for card.
4. When the hand is over, the key is filed with the hand.

Anyone can then hash the key and see the fingerprint that was written down before the deal, and rebuild the deck from the key and see the cards that were dealt. A deck changed during the hand, say to react to how you bet, would not match.

In the app, open Settings, then How dealing works. Under Check a hand is any recent hand of yours with its key, its fingerprint and a Verify button, and a link that opens it in the checker on this site, which rebuilds the deck in your browser with its own code.

What a lock proves, and what it doesn't

A lock proves the deck was fixed before the first card and never changed during the hand. On its own it can't prove the key was drawn fairly. That is what the tests below are for: millions of deals from the code the app runs, checked against what a fair deck does. The method and the code are published here so anyone can read them.

No outside firm has audited the shuffle. These are our own tests, and every one of them is on this page.

The bots never see your cards

The bots decide from what a player at a real table could see: their own cards, the board, the bets. To check, the report makes bot decisions twice from the same starting point, the second time with your cards swapped for two others. If a bot looked at your cards, some decisions would change. None did.

Hands that aren't shuffles

The welcome hand, the lessons and Watch it back deal cards set up in advance, on purpose. They have no lock, the app doesn't list them as shuffled hands, and they aren't counted in your numbers.

Every test

Each line says what was counted, over how many deals, what a fair deck gives and what came. The last number is how often a fair deck would be at least this far from what it gives: a test fails below 1 in 10,000. With this many tests a fair deck lands below 1 in 20 on a few of them, about one in every twenty tests, and that is what to expect.

All in: did the favourite hold?

The first two seats of every hand, played as if both were all in on the turn. For each, every river that could come was counted, so the cards say how often each hand should win. Then the real river was dealt. If the deck favoured or punished anybody, what happened would drift from what the cards said.

Every game

Every game the app deals, every hand's lock checked, and every card counted as the first one dealt.

Check a hand yourself

Paste a key and a fingerprint, or open a hand from the app, and your browser rebuilds the deck.

Download the deals

The first 100,000 hands from the report, with their keys, fingerprints and the cards in the order they were dealt, so you can run your own tests.

For the technical

Card order before the shuffle: spades 2 to ace, then hearts, diamonds and clubs (a short deck leaves out the twos to fives). In a draw game that runs out of cards, the thrown cards are shuffled again with a shuffle seeded from the locked deck and the cards thrown, so that is fixed by the lock too.

The whole report, with every number on this page: report.json.