Mage Slayer (Revised)

You have practiced techniques useful in combat against spellcasters, gaining the following benefits:

• When a creature within your melee range starts casting a spell, you can use your reaction to make a melee weapon attack against that creature. If the attack hits, the caster must make a concentration save (with disadvantage, as implied below) or lose the spell.
• When you damage a creature that is concentrating on a spell, that creature has disadvantage on the saving throw it makes to maintain its concentration.
• You have advantage on saving throws against spells cast by creatures within your melee range.

Note: This is a homebrew feat. Ask your DM before using it.