View source for SRD:Special Initiative Actions

=====Readying to Counterspell=====

You may ready a [[SRD:Casting Spells#Counterspells|counterspell]] against a spellcaster (often with the trigger "if she starts casting a spell"). In this case, when the spellcaster starts a spell, you get a chance to identify it with a [[SRD:Spellcraft Skill|Spellcraft]] check ([[DC]] 15 + spell level). If you do, and if you can cast that same spell (are able to cast it and have it prepared, if you prepare spells), you can cast the spell as a counterspell and automatically ruin the other spellcaster’s spell. Counterspelling works even if one spell is divine and the other arcane.

A spellcaster can use [[SRD:Dispel Magic|''dispel magic'']] to counterspell another spellcaster, but it doesn’t always work.