Identifying a spell

[GoodbyeSoberDay]

Now, I understand there are no actual book rules to identify a spell being cast. That said, what (house) rules work for you, at your table? We've been using the same check as one would for copying a spell scroll; i.e., Int (Arcana) check DC 10+spell level to identify, as long as you can actually perceive the spell being cast.

[Kane0]

You know most spells names and basic functions, and if there is a good reason you wouldn't know or want to know details then an Arcana check will usually tell you. DC would usually be between 5 + spell level to 15 + spell level depending on level of detail and rarity of the spell. The sorcerer's subtle metamagic also counteracts the ability for most to identify their spell should they be able to notice that they are casting in the first place.

This way counterspell works quite well for us, and the DM can choose to make some spells mysterious or dramatic for thematic reasons without difficulty.

[Louro]

I started with the DC check.
Then, on a second through and after a group debate we throw the identification DC check from 3.5.

Right now players can tell the difference between a cantrip (sort of swift and simple casting), an arcane spell and a divine one. And that's it.
Command is just a word, so you can never tell if it is just a word or the spell.

However they can identify common spells by seeing their effects. Some uncommon by an arcane check.
Every wizard has its own "style" when it comes to casting, which is even more different for sorceress, and even more for bards. Cleric casting might vary by miles from one god to another.

Identify a casting is an obsolete mechanic that has no place in 5e, IMO.