Coin Flip

Coin Flip tosses a coin, or up to a thousand at once. A single flip settles an argument; a thousand shows you something a single flip cannot, which is why the tally is the part of this page worth having.

Watch the heads share as the count grows. At ten flips it might be seventy per cent; at a hundred it will usually be within ten of fifty; by a few thousand it sits very close indeed. That is the law of large numbers, and this is one of the few places most people ever watch it happen rather than read about it. What it does not do is make the next flip any more likely to balance things out — each flip is independent, and the share converges because later flips dilute the early run, not because anything corrects it.

Each flip comes from the browser's cryptographic random source, one bit at a time. A real coin is very slightly biased towards the side that started facing up; this one is not biased at all.

• One flip, or up to a thousand at once
• Call heads or tails before flipping
• A running tally across the whole session
• The heads share as a percentage
• Cryptographic randomness, with no bias towards either side
• Nothing stored and nothing sent anywhere
• Readable by a screen reader, with the result announced
• Resets the tally without reloading the page

The coin flip is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Settling a decision between two options
• Choosing who goes first
• Showing how a random share settles towards a half
• Generating a long run of random bits
• Demonstrating that streaks are normal rather than suspicious