Can you cast a spell during the draw step before you draw your card?

The draw step has a strict sequence defined by the Comprehensive Rules. When the draw step begins, the active player immediately draws a card as a turn-based action (CR 504.1). Turn-based actions are not spells or abilities — they happen automatically without any player receiving priority first.

Priority is only granted to players after all turn-based actions for a step have been completed and the game checks for state-based actions (CR 117.3a). This means no player can cast a spell or activate an ability before the mandatory draw occurs — there is simply no window to do so.

This is different from, say, the upkeep step, which has no turn-based actions, so the active player receives priority immediately and can cast instants or activate abilities right away (CR 503.1).

Concrete example: You are at 1 life and your opponent controls a Thassa's Oracle. At the start of your draw step, you cannot cast a Lightning Bolt to kill the Oracle before you draw your card — you must draw first, then priority is passed and you may act.

The relevant rules are CR 504.1 (draw step turn-based action) and CR 117.3a (when players receive priority), which together confirm the draw happens before any player can cast spells.