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Verify a draw

Got the link of a draw? Paste it here and see whether the result checks out.

Paste the link you received. The check runs in your browser.

Draw receipt

Guide and details

Paste a verification link. The winners are recomputed from the seed and the list, here in your browser.

What the check does

A verification link from the wheel or the name picker contains the time of the draw, the full list in order, the winners, the seed and a fingerprint. This page ignores the recorded winners, computes them again from the seed and the list, and compares. It also recomputes the fingerprint.

The method, so you can check it without us

The calculation is short enough to reproduce in any language with SHA-256.

  1. The seed is 32 random bytes from crypto.getRandomValues, written as 64 hexadecimal characters.
  2. Block i of the random stream is the SHA-256 of the text seed:i, with i starting at 0. Each block is read as eight 32-bit numbers, most significant byte first.
  3. Each draw uses two numbers from the stream: the lower 21 bits of the first followed by the 32 bits of the second, a 53-bit value. If the value is not below the largest multiple of n that fits in 253, it is discarded and the next two numbers are used. The result is the value modulo n.
  4. For winners without repeats, start from the positions 0 to n − 1. For the k-th winner, counting from 0, draw a number below n − k, add k, and swap that position with position k. The first positions are the winners, in order. When repeats are allowed, each winner is simply one draw below n.
  5. The fingerprint is the SHA-256 of the JSON text {"participants":[…],"seed":"…"}, with the list in order and no extra spaces.

Limits worth knowing

A passing check ties the winners to the seed and the list. It says nothing about how the list was put together, and it cannot show that the organiser drew once. If a draw matters, ask for it to be made live and for the verification link to be published straight away.

Why use Choose Tools

  • One source of randomness

    Every draw calls crypto.getRandomValues and throws away the values that would cause modulo bias. A test fails if Math.random ever appears in the source.

  • The result comes first

    The wheel, the coin and the dice pick the outcome before they move. The animation always has the same length and only shows what was drawn.

  • A receipt you can recompute

    Wheel and name-picker winners are derived from a 256-bit seed with SHA-256. The Verify page repeats the calculation and compares.

  • Lists stay on your device

    They are kept in local storage. Shared links carry the list after the #, which browsers do not send to servers. There is no account.

  • Quiet by default

    Sound is off until you turn it on, and with “reduce motion” set in your system the result appears with no animation.

Questions and answers

What does a passing check prove?

That the recorded winners are exactly what the recorded seed produces over the recorded list, and that the list and seed match the fingerprint. Changing a name, the order or the winner makes the check fail.

What does it not prove?

That the draw was made only once. The seed is created at the moment of the draw on the organiser’s device, so an organiser could draw again and show only the result they prefer. A live draw or a screen recording covers that gap.

Is the list sent to your server when I verify?

No. The receipt sits after the # in the link, and browsers do not send that part of an address. The check runs in the page.