Spell Steal

5th-level abjuration

Casting Time: 1 reaction, which you take when you see a creature withing 60 feet of you casting a spell
Range: 60 feet
Components: V, S
Duration: Concentration, up to 10 minutes.

You attempt to snatch a spell from a creature in the process of casting within range. If the creature is casting a spell of 3rd level or lower, the spell has no effect and is stolen. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell’s level. On a success, the creature’s spell has no effect and is stolen. A stolen spell is stored inside you or your arcane focus for the duration of the spell.

As long as you are concentrating on Spell Steal, you can cast a stolen spell using the spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell. A spell casted in this way does not require you to consume a spell slot. The effects of this spell end when a stolen spell is casted.

If you do not cast the stolen spell for the entire duration of the spell, the spell is etched into to your memory. A stolen spell that is etched into your memory requires no concentration to hold and can be cast using the spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell. While a spell is etched into you memory, you may add it to your spellbook given that you have the necessary materials and time required to copy it. A stolen spell remains etched into your memory until you cast it, copy it to your spell book, or finish a long rest.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, a spell that is two levels or lower than the spell slot you used has no effect and is stolen.