Is it really random?
Numbers come from crypto.getRandomValues, the browser’s cryptographically secure random source, not the predictable Math.random. Out-of-range values are thrown away and redrawn instead of using a plain remainder, so every number in the range is exactly equally likely.
Lucky draws and raffles
Number your entries from 1 to N, set the range, tick “no duplicates” and choose how many winners you need. Each number can then come up only once, just like drawing slips from a box. For lottery-style picks, set for example 1 to 49 and 6 numbers.
Limits
Up to 10,000 numbers per draw, and any whole numbers between about −9 quadrillion and 9 quadrillion.
Is anything sent to a server?
No. Every calculation runs in your browser. Nothing you type here is uploaded or stored anywhere else.