How the flip works
Each flip is an independent draw with probability 1/2 for heads and 1/2 for tails. The page uses the browser's cryptographic random number generator (crypto.getRandomValues) and rejection sampling, so there is no bias toward either side.
Physical coins are very close to fair, but not perfectly. Researchers have measured a slight tendency to land on the side that started face up. A virtual flip has no such tendency.
What to expect from many flips
The share of heads approaches 50% as the number of flips grows, but the count itself wanders. In 100 flips, anything from about 40 to 60 heads is ordinary; the standard deviation is √(n × 0.5 × 0.5) = 5 flips.
Streaks are longer than intuition suggests. In 100 flips, a run of 6 or 7 identical results is typical. Past flips never change the odds of the next one.