How the teams are made
The names are shuffled with a Fisher–Yates shuffle driven by your browser's cryptographic random number generator, so every arrangement is equally likely. Then people are dealt out one at a time like cards, which keeps team sizes within one of each other.
Number of teams or people per team
Choose “Number of teams” to get exactly that many groups. Choose “People per team” to get as many teams as needed with at most that many people each — 10 people in teams of 4 becomes 4, 3 and 3 rather than 4, 4 and 2.
Tips
Blank lines are ignored, and your list is saved in this browser so you can reshuffle later. Press Make teams again for a new draw. Everything happens on your device; the names are never uploaded.