Does a mana ability go on the stack and can it be countered?

A mana ability is defined in CR 605.1 as an activated or triggered ability that could produce mana and meets specific criteria (it doesn't target, and isn't a loyalty ability). The critical rule is CR 605.3a: activated mana abilities don't go on the stack — they resolve immediately when activated.

Because mana abilities never enter the stack, no player receives priority after one is activated (CR 605.3b). This means spells like Stifle or Disallow that counter activated or triggered abilities cannot target or counter a mana ability — there is simply no stack object to target or counter.

This rule exists for practical game flow: if tapping a Forest for green mana could be countered or responded to, casting any spell would become an endlessly interruptible chain, grinding the game to a halt.

Concrete example: Your opponent taps a Llanowar Elves to add {G} to their mana pool. You cannot cast Stifle in response, because the Elves' ability is a mana ability — it never went on the stack in the first place, and the green mana is already added.

Note: not every ability that produces mana is a mana ability. If an ability has a target, it is not a mana ability (CR 605.1b) and does use the stack normally, meaning it could be countered.