Counterspell doesn’t work how you’d think

 Apparently. See Bilbron’s yt on “tactical aspects of combat, efficiency" (this is 5e  D&D) https://www.youtube.com/watch?v=t-4Ci4EEPwE

Comments talk about it too.  

Says… u cant know what spell is being cast AND cast counterspell at same time. Why? Well, RAW…

A. It takes a reaction to do Arcana check to see if u know what spell it is. 
B. It would take another reaction (only one per round per character) to do the Counterspell.
Seems most ppl just ignore that detail. 

***i think i see a way. Two casters and one checks arcana, then yells out what spell it is, while other caster then uses the Counterspell.