Does a wizard need to attune to the magical spellbooks in Tasha's Cauldron of Everything in order to use them as spellbooks?

Question

The wizard at my table does not have any available attunement slots and just discovered an Alchemical Compendium. We are trying to determine if he could use the spellbook only for the spells contained within if he chooses not to attune it. Clearly, he would not be able to use the book's charges and abilities that typically become available by attuning to a magic item.

Does he need to attune to the Alchemical Compendium to use it at all (i.e. even as a regular spellbook)? Or can he "use it as a spellbook" without attunement?

Answer 1

Functioning as a spellbook is a “nonmagical benefit”, so it does not require attunement.

The rules for attunement state:

Without becoming attuned to an item that requires attunement, a creature gains only its nonmagical benefits, unless its description states otherwise.

So any nonmagical benefits of the spell book can be used without attunement. Since a Wizard’s usual spell book is not actually a magic item, just a collection of spell texts, functioning as a spell book is a nonmagical benefit - it’s a benefit you can get from a nonmagical version of this item. So yes, you can use an Alchemical Compendium as a spell book without attuning.

Some magical spellbooks have features that obstruct their use to non-attuned persons.

For example, consider the Crystalline Chronicle, a crystal ball that can function as a spellbook:

While you are touching the crystal, you can retrieve and store information and spells within the crystal at the same rate as reading and writing. [...] It functions as a spellbook for you, with its spells and other writing psychically encoded within it.

In this case, using the Chronicle as a spellbook is a magical benefit, since mundane crystal spheres don't magically store spells or psychically encode anything.

Another example is the Duplicitous Manuscript. To non-attuned persons, the book appears to be nothing more than a smutty romance novel:

To you, this book is a magical spellbook. To anyone else, the book appears to be a volume of verbose romance fiction.

Obviously, if you are not attuned to this book, you will not be able to cast spells from it.