How to run a Provably Fair Giveaway using Bitcoin Blockhash?

To run a provably fair giveaway, enter the list of competitors, specify the target Bitcoin block number, and the number of winners. The tool will use the blockhash of the specified block to randomly select winners from the list of competitors.

Bitcoin Giveaway Manager

Manage your giveaways easily. Pick winners using provably fair method based on bitcoin blockhash.

Instructions

One competitor per line

Paste your list of participants, one name or identifier per line.

Set a target block

Enter the Bitcoin block number whose hash will seed the random draw.

Provably fair

Winners are derived from the blockhash — verifiable by anyone on the blockchain.

Shareable link

Generate a link to share your giveaway setup — data is encrypted client-side.

Participants

How many winners?

Target Block

Results

Block hash:

Decimal number:

Winner:

How the draw works

As the blockhash is just a number, its last 6 digits are converted to decimal using this function:

var decimal = parseInt(blockhash.slice(-6), 16);

Now we have an integer (0 to 16777215) from the blockhash.

After dividing this decimal by the number of participants, we use the modulo operator (%) to get the division remainder, which becomes the index_number.

var index_number = decimal % competitors.length;

         var winner = competitors[index_number];

For additional winners, past winners are removed from the list and one more digit is added from the blockhash.