Does Gaea's Cradle tap for mana equal to the number of creatures at the moment of tapping or at resolution?

Gaea's Cradle has a mana ability that reads: '{T}: Add {G} for each creature you control.' Like all abilities, the effects of this ability are determined when it resolves, not when it is activated. This is governed by CR 605.3, which states that a mana ability resolves immediately after it is activated, and the game checks the board state at that moment of resolution.

Because mana abilities resolve immediately (CR 605.3a) without using the stack in the normal sense, there is almost no window for the board state to change between activation and resolution in a typical scenario. However, the key principle remains: the creature count is evaluated at resolution (CR 107.3), not at the moment you tap the land.

In the rare edge case where something could somehow alter the board between the tap and resolution — which is essentially impossible for a mana ability since it doesn't use the stack and players cannot respond — the resolution moment is still the legally correct reference point per the rules. The practical answer is that the count is taken at the instant the ability produces mana.

Concrete example: You control 5 creatures and tap Gaea's Cradle. The mana ability resolves immediately. At that moment you still control 5 creatures, so you add {G}{G}{G}{G}{G} to your mana pool. If somehow you controlled only 4 creatures at resolution (hypothetically), you'd get only 4 green mana.

Relevant rules: CR 605.1 defines mana abilities; CR 605.3a explains they resolve immediately; CR 107.3 covers how values are determined at the time effects are applied.