This tool picks uniformly among the twelve calendar months, January through December, using the Web Crypto API for the underlying randomness. It's useful for icebreaker games ("what's your random month?"), randomly assigning a review or audit month, picking a month for a giveaway drawing, or generating placeholder scheduling data. By default each pick is fully independent, but you can switch on "avoid repeats" for a batch so every month shows up once before any month repeats — the same logic as shuffling a deck of 12 cards rather than drawing with replacement.
Yes, in plain random mode each of the 12 months has exactly a 1-in-12 chance on every single draw, regardless of what's been picked before.
It shuffles the 12 months and hands them out in that shuffled order, so within any batch of up to 12 draws no month repeats — once all 12 have appeared, the cycle reshuffles and starts over. It's the same idea as dealing from a shuffled deck instead of picking cards with replacement.
Yes — once the current shuffled cycle of 12 is exhausted, the tool reshuffles and continues, so a batch of, say, 20 will show all 12 months once, then 8 more months from a freshly shuffled next cycle.