Check a game’s dice

A free tool · Last updated 28 October 2026

When a game against a bot ends, Backgammon Room shows the key its dice came from. Paste it here and this page works out every roll again, so you can see they’re the rolls you played. It all happens in your browser: nothing you enter leaves this page.

The checker runs in your browser and needs JavaScript, which seems to be off. You can still check by hand with the recipe below.

Which game?

Against a bot Online match

Key

Once the game is over, Game info (ⓘ on the board) shows it under Dice: tap Copy beside it.

Lock (optional)

Just under the key: the fingerprint the game showed before move 1.

Did the game begin with an opening roll?

Yes No

Yes for a single game or a match’s first game. In a match, the winner of each game starts the next without one.

Take-backs made before these rolls

Only in a Practice game: after each take-back the rolls carry on from a fresh line. Otherwise leave it at 0.

The rolls you saw (optional)

In the order they came, starting with the opening roll, for example 4-6 1-3 6-6. Each is compared with the key’s.

What it checks

Before the first roll of a game against a bot, your iPhone picks a secret key and shows its fingerprint, the lock. Every roll comes from the key and the roll’s number, so once the game has started no roll can change, whatever you play and whatever the bot’s level. When the game ends, the key is revealed.

This page hashes the key to see that it gives the lock, then works out every roll from it. If the lock matches and the rolls are the ones you played, the dice were fixed before the game began: neither the app nor the bot chose them. Online, the server seals its number the same way before the first roll and both apps add a number of their own, so no one alone decides the dice. How the dice work explains it all in plain words.

Check it without this page

The lock is the SHA-256 of the key’s 32 bytes. A roll is read from HMAC-SHA256, keyed with the key, of the roll’s label followed by :0 (then :1, :2… if more bytes are needed): a byte of 252 or more is skipped, any other gives a die of (byte mod 6) + 1, and the first two dice read are the roll.

Against a bot, the opening roll’s label is bg-dice-v1:opening:0 (:1, :2… after a tie; your die first) and each turn’s is bg-dice-v1:turn:2, bg-dice-v1:turn:3… The opening roll’s winner plays it as turn 1. A later game of a match has no opening roll and starts at bg-dice-v1:turn:1. In a Practice game, after a take-back: bg-dice-v1:turn:7:line:1.
Online, the key is HMAC-SHA256, keyed with the server’s number, of bg-online-v1:seeds: followed by both apps’ numbers in lowercase hex, separated by a colon. The labels are bg-online-v1:g1:opening:0, then bg-online-v1:g1:roll:1, …:roll:2… (g2 for the second game, which starts at roll:1).
A test: with the key 00 01 02 … 1f, the lock starts 630dcd29, the opening roll is 4-6 and turn 1’s roll would be 5-4.

In Python, with nothing to install:

import hashlib, hmac

key = bytes.fromhex("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f")
print(hashlib.sha256(key).hexdigest())  # the lock

def roll(label):
    dice, block = [], 0
    while True:
        for byte in hmac.new(key, f"{label}:{block}".encode(), hashlib.sha256).digest():
            if byte < 252:
                dice.append(byte % 6 + 1)
                if len(dice) == 2:
                    return dice
        block += 1

print(roll("bg-dice-v1:opening:0"), roll("bg-dice-v1:turn:2"))  # [4, 6] [1, 3]

Questions

Is anything I enter sent to you?: No. The page works everything out in your browser, and the site has no analytics or cookies.
Do I have to enter my rolls?: No. Without them the page lists every roll the key gives, to compare with the game’s replay. With them it compares each one for you.
What if a roll doesn’t match?: Check that the rolls are in the order they came, that the key and the lock come from the same game, and the answers about the opening roll and take-backs. If the key matches the lock and a roll still differs, tell us with the game’s key.

More free tools: Should I double? and the race and shot calculator.