You may have started out as a street magician or an unrespected magic initiate but by now you have clawed your way to the top. No one knows the things you have done and stole to become the wizard you are today. You will show them who the real master is. With Arcane Thief subclass you will learn to take magical power for yourself.

Pocket Magic

Beginning when you select this school at 2nd level, you can copy spells from spell scrolls in half of the time.

Arcane Inquisitor

Starting at 2nd level, you have a skilled eye for discerning the magical world. You gain the Detect Magic spell which you can cast at will without expending a spell slot. This spell does not count against your known spells and is always prepared.
Additionally you have advantage on Concentration checks made to maintain this spell.

Magical Extortionist

At 6th level, you have become a specialist in thwarting the efforts of other spellcasters and can learn from their failures. You gain the Counterspell spell. This spell does not count against your known spells and is always prepared.
When you succeed on your Counterspell you may roll an Arcana check against a DC of 8 + (twice spell’s level). On a successful check, you have temporarily memorized this spell and you gain the ability to attempt to copy the countered spell to your spellbook for the next 24 hours. When copying a spell in this way you can do so at half the gold cost and time. You lose the ability to copy this spell after 24 hours or a long rest, whichever comes first.

Mystic Opportunist

At 10th level, you are adept at stealing arcane power from others. When you succeed in countering a spell using Counterspell, you regain a spell slot equal to half that of the spell which was countered rounded down.

Wizard's Bane

Starting at 14th level, you are unparalleled in thwarting the magical efforts of those you encounter. You have advantage on Intelligence (Counterspell) checks while under the effects of the Detect Magic spell.