Toilet valve leaking at the base

A leak at the base of the toilet valve is usually the seal between the valve and the bowl base, which wears out from repeated flushing over the years — it's a cheap, common part. Before replacing anything, confirm it's actually leaking at the base and not water splashing from the bowl during flush, which looks similar but is a totally different fix (usually a worn flush ball seal). Turn off the water supply and watch exactly where the water first appears. Is it leaking with the water on and off, or only during a flush?