Flip a Coin
A fair coin, plus the tally that makes it worth flipping more than once. The streak is the interesting number — runs of five look wrong and are not.
Heads
0
Tails
0
The last twenty
What this tool does
A fair coin with a scoreboard. One press gives you heads or tails; the tally underneath keeps the running counts, the current streak, and the last twenty results as a row of chips. That tally is the reason to use this rather than a coin on a table: people are reliably bad at judging whether a sequence is random, and seeing five heads in a row in your own results is a far better demonstration of what randomness actually looks like than any explanation.
Two honest limits. The flip is JavaScript’s Math.random(), which is a fair coin for a game and is not a source of cryptographic randomness — nobody is securing anything with a coin toss, but the page does not claim more than it has. And on a small number of flips the percentages swing wildly: ten flips landing 70% heads is not evidence of a biased coin, it is what ten flips look like. The tool says so rather than letting the number imply otherwise.
How to use it
- Press Flip the coin for a single result. The button locks for a moment while the animation runs, so a double-click cannot produce two flips.
- Watch the tally underneath. Heads and tails counts, the current streak, and the last twenty results all update together.
- Press Flip ten times if you want to see a distribution rather than a single result. Ten flips at once is where the tool gets interesting.
- Press Copy the result to paste the last flip and the session tally into a message.
Common use cases
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Settling an argument
One flip, one answer, and the tally means you can go again without losing track of what has already happened.
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Demonstrating randomness
Flip ten at once and count the heads. Runs that look suspiciously long turn up far more often than people expect.
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Deciding something arbitrary
Who goes first, who pays, which way to walk. Low stakes and immediate.
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Teaching probability
The running percentage converging towards 50% over a few hundred flips is a decent demonstration, and the streaky path it takes to get there is the more interesting lesson.
Frequently asked questions
Is the coin fair?
Yes. It is a fifty-fifty draw with no weighting and no memory of previous flips. It is not cryptographic randomness, and it does not claim to be, but for a game it is a fair coin.
Why did I get five heads in a row?
Because that happens. Over twenty flips, a run of four or five in a row is unremarkable — people consistently underestimate how streaky real randomness is. The last twenty chips are shown so you can see the pattern rather than imagine it.
Does the tally persist if I reload?
No. Everything is held in the page, and reloading or closing the tab clears it. There is a Reset button if you want to clear it without reloading.
What does Flip ten times do?
It rolls ten independent flips at once and adds them all to the tally. It is the quickest way to see a distribution rather than a single result, and the summary line afterwards explains why ten is still a very small sample.