Plinko Name Picker

What it is for

Whoever runs a draw is often suspected of steering it. The Plinko Name Picker drops a ball through rows of pegs and the slot it lands in picks the name. Behind the fun board there is a proof: the organiser shows a SHA-256 fingerprint of a secret before the drop, a guest adds any word afterwards, and when the secret is revealed anyone can replay the exact drop on this page.

The same engine runs the plinko board in the Party Picks section of Fieldday, which creates the secret for you, animates the ball and keeps the history of earlier draws. Use the tool page to check such a draw, or to run one from a script or an AI agent through the JSON API.

Worked example

Six friends choose who picks tonight's film. Names: Ana, Ben, Cleo, Dev, Eli, Fay, How many to pick 1, Peg rows 12, Secret 7f3a9c2e51d84b06, Audience word pineapple.

Before anyone presses a button, the organiser shares the fingerprint 12d4d190…e4b0a32d. It is the SHA-256 of the text shown under "Fingerprint input": fieldday-party-v1|plinko|{"names":["Ana","Ben","Cleo","Dev","Eli","Fay"],"picks":1,"rows":12}|7f3a9c2e51d84b06.

The result: "Cleo wins the plinko draw (each of the 6 names had a 16.67 % chance)." The board has 12 slots because short lists repeat until there are at least 8 slots, so every name sits on exactly two of them. The ball hit 21 pegs, fell for 4.717 seconds and landed in slot 7.

The audience word really matters. With the same secret, "banana" makes Eli the winner and "kiwi" picks Dev, while the fingerprint stays the same. So the organiser could not know the result when the fingerprint was shared.

The second example picks three raffle winners from ten names: Emma, Omar and Noah. Each winner leaves the board, so the later balls fall on 9 and 8 slots.

How to read the result

• Winner or First pick is the name in the slot where the first ball landed. The Picks table lists every ball with its slot, the number of slots on that board, peg hits and fall time.
• Chance of each name is always 1 divided by the number of names. Before every drop the names are shuffled onto the slots, so it does not matter that the board favours some slots.
• Fingerprint (SHA-256) must match what the organiser published before the drop. Hash the "Fingerprint input" text with any SHA-256 tool to check it yourself.
• The fairness check shows two bar charts. In the example the slots received between 22 and 81 of the 500 test balls, so the board is clearly not uniform. The names got 43 to 58 wins each, close to the expected 50, and the chi-square value of 6.84 with 9 degrees of freedom is normal for a fair draw.

Tips and common mistakes

• Never leave Secret empty for a real draw. Without it the secret is derived from the names, the tool warns that the draw is predictable, and anyone could work out the result in advance.
• Publish the fingerprint first and only then ask for the audience word. If the word comes first, the organiser could try secrets until they like the outcome.
• Changing the order of the names, the peg rows or the number of picks changes the fingerprint. Copy the inputs exactly when you verify a draw.

FAQ

Is a physics board really fair?

The board on its own is not: balls land in the middle more often. Fairness comes from the shuffle before each drop. Every name is equally likely to sit on every slot, so each name wins with exactly the same probability.

Does the replay match in every browser?

Yes. The physics uses only basic arithmetic and square roots, which every JavaScript engine computes identically.

What stops the organiser from choosing a convenient secret?

The fingerprint is published before the audience word exists. Changing the secret afterwards would change the fingerprint, and the word makes it impossible to predict the result while picking a secret.

Can I use it for an official lottery?

It is meant for games, chores and small prizes. Regulated lotteries have their own legal rules on how draws must be run and supervised.