Counterspell

3rd-Level Abjuration
Casting Time: 1 reaction
Range: 60 feet
Components: S
Duration: Instantaneous

You attempt to interrupt a creature in the process of casting a spell.

Trigger. You see a creature within 60 feet of you casting a spell.

Effect. If the creature is casting a spell of 2nd level or lower, its spell fails and has no effect. If it is casting a spell of 3rd-level or higher, make an ability check using your spellcasting ability (DC 10 + the spell’s level). On a success, the creature’s spell fails and has no effect.

Special. The creature can use its Reaction to try to reshape the fraying magic and cast another spell with the same casting time so long as it is of a spell level equal to or less than half the original spell.

At Higher Levels. The interrupted spell has no effect if its level is less than the level of the spell slot you used.

Source: PHB 228, SRD

Changelog

Altered the spell to only auto-counter a spell that is less than the level of the counterspell.
Added the ability for a counterspelled creature to use their Reaction to cast another less powerful spell.