What "random" means in this generator
Each number this tool produces is drawn uniformly: every value in the range is equally likely, and draws do not influence each other (unless you switch duplicates off, which samples without replacement). The engine is the browser's built-in Math.random, a pseudorandom generator: it runs a deterministic algorithm from a seed you never see, producing sequences that pass statistical tests for uniformity and independence well enough for simulations, sampling exercises, games and teaching. It is not built for cryptography; do not generate passwords or keys with it.
With and without replacement
The toggle matters more than the range. Drawing with replacement models dice, coins and most Monte Carlo work: the pool never changes, and repeats are not just allowed, they are expected (in 10 draws from 1 to 100, a repeated value somewhere is unremarkable; in 100 draws it is a near-certainty by the birthday effect). Drawing without replacement models lotteries, shuffled decks and survey samples from a list: each value can appear once at most, which is why the count cannot exceed the size of the range.
A teacher needs 12 distinct students from a class numbered 1 to 30. Set minimum 1, maximum 30, count 12, duplicates off: the tool returns 12 different numbers in one click, a simple random sample of the class list. Leave duplicates on and the same settings mimic 12 independent dice-style picks, where a student could be picked twice.
Rerolling until the draw "looks random". Human eyes flag clusters and repeats as suspicious, but genuine uniform draws are full of them. A draw with no repeats and even spacing is the unusual one; filtering for prettiness quietly destroys the uniformity you wanted.
Frequently asked questions
Are these numbers truly random?
They are pseudorandom: generated by an algorithm, but statistically uniform and unpredictable enough for simulations, sampling and games. They are not suitable for passwords, keys or anything security-critical.
Why did I get the same number twice?
Because duplicates are on. With replacement, every draw is independent, so repeats happen naturally. Turn duplicates off to sample without replacement.
How many numbers can I generate at once?
Up to 10,000 per click. For a no-duplicates draw, the count cannot exceed the number of values in the range.