Mastering a Foreign Spellbook

Magic is as much art as science, and each wizard uses their own unique notation when adding a spell to their spellbook. Two wizards who learned the exact same spell from the exact same mentor recorded the spell differently and use slightly different verbal, somatic, and material components. If a wizard finds themselves in possession of another wizard's spellbook, they are unable to use that spellbook unless they take the time to master the intricacies of the other wizard's version of the spell.

If you’re a wizard, you can spend 1 day of downtime to master up to four levels of spells from a foreign spellbook. You must spend 2 hours and 10 gp per spell level studying the different notations and practicing with the mix of components. Once you have mastered a spell from that book, you may now use that book to prepare the spells you've mastered. It may take days or weeks to master every spell in a foreign spellbook.

You don't have to master every spell in a foreign spellbook to use it. You can access the spells you have mastered, you're just unable to use the spellbook to prepare spells you haven't mastered, or copied into your own spellbook.