Spellcraft - When?

[Echoen]

When an NPC is casting a spell, which of the following happens?

The DM announces a spell is being cast and requests spellcraft checks of the players,

or

Players must announce they are using spellcraft to identify the spell?

[Noctani]

Echoen wrote:

When an NPC is casting a spell, which of the following happens?

The DM announces a spell is being cast and requests spellcraft checks of the players,

or

Players must announce they are using spellcraft to identify the spell?

Both

If it's the first time the PCs are encountering this NPC or Monster with class levels.The DM should describe the casting in the form of somatic or verbal components or roll something to hide it vs perception to see if they catch it. If the PCs are up against a known opponent PCs need to speak up. The DM shouldn't waste time on spellcraft checks unless the PCs need to know. If the DM describes the action but none of the players catch it, then they MAY not be able to identify it, DM discretion. If DM describes nothing, but a spell-like affect occurs the players should be able to ask for a spellcraft check.

Regardless, no one can catch everything. Work together, not against each other.

[wraithstrike]

I as a GM ask for spellcraft checks to remind the players to make them.

[Eridan]

Dont forget the DC modifiers for Spellcraft checks which can be found under Perception.
+5 for distraction or +2/+5 for bad conditions can be applied in most fights and +1/10ft distance can be important as well.