Can you activate mana abilities while the stack is not empty?

Mana abilities are a special category of activated abilities (or triggered abilities) that produce mana and meet specific criteria. Because they are so fundamental to gameplay, they are granted a unique privilege: they do not go on the stack and therefore do not require priority. This means you can activate them at virtually any time you need mana, including while spells or abilities are already on the stack.

An activated ability is a mana ability if it could add mana to a player's mana pool when it resolves, is not a loyalty ability, and does not have a target (CR 605.1a). These abilities skip the normal priority and stack process entirely — they are activated and resolve immediately (CR 605.3a).

This is critical for casting spells: when you cast a spell and need to pay its mana cost, you are in a window where the spell is being cast but hasn't been placed on the stack yet. You can activate mana abilities during this payment process to generate the mana you need (CR 601.2g). Similarly, if an ability on the stack requires mana to be paid upon resolution (like a kicker or an additional cost trigger), you can tap lands or use other mana abilities right then.

Concrete example: Your opponent casts Counterspell, targeting your creature spell. Both spells are now on the stack. You want to cast Autumn's Veil in response. Before you put Autumn's Veil on the stack, you can tap your Forest for green mana — even though the stack is not empty — because tapping a Forest for mana is a mana ability that bypasses the stack entirely.

Note: Abilities that happen to produce mana but also have a target (e.g., Selvala, Heart of the Wilds's group-hug ability targeting another player) are not mana abilities and do use the stack normally (CR 605.1b). Always check whether the ability meets all the criteria in CR 605.1a.