Can you substitute the pact of the Tome's Book of Shadows with a Spellshard?

Question

Can you substitute the pact of the Tome's Book of Shadows with a Spell Shard?

Spellshard

Wondrous item, common

This polished Eberron dragonshard fits in the hand and stores information similar to a book. The shard can hold the equivalent of one book that's no more than 320 pages long. A shard can be created blank or already filled with information. When the shard is created, the creator can set a passphrase that must be spoken to access the information stored within.

While holding the shard, you can use an action to open your mind to the shard, seeing its content in your mind. On subsequent rounds, reading the text or scribing new text on blank "pages" in the shard requires concentration (as if concentrating on a spell) and takes the same amount of time it takes you to read and write normally. Thinking of a particular phrase or topic draws you to the first section in the shard that addresses it.

A wizard can use a spellshard as a spellbook, with the usual cost in gold and time to "scribe" a spell into the shard.

Since the Spellshard is pretty much an Arcane I-pad, Kinddle or E-reader and mechanincaly its a spell book with better bookmarks.

Answer 1

Replacing an existing Book of Shadows with a found Spellshard: No

If an existing warlock who has the Pact of the Tome feature finds a Spellshard, they definitely cannot start using it as their Book of Shadows. The Book of Shadows is created by the warlock's patron, and no warlock feature allows duplicating or transferring its magical properties. The only way to get a new Book of Shadows is to perform a ceremony and receive the new Book from your patron.

Requesting a Spellshard-like Book of Shadows from your patron: Maybe

The Pact of the Tome feature does not provide much detail about what a Book of Shadows can look like. While the Wizard has a small portion of a sidebar indicating that a Spellbook does not need to actually be a book, making a clear case for various other things that can hold writing, the Warlock has no similar section that I can find.

That said, I doubt a DM would have a problem with Warlocks deciding on the details of the appearance of a Book of Shadow, probably including "magical iPad" if it is appropriate for the campaign setting and patron. It wouldn't necessarily have the exact effects of a Spellshard, but something aesthetically similar is likely to be within reason.

Answer 2

The Book of Shadows is not a spellbook; no.

Although it functions similarly once you take the Book of Ancient Secrets invocation, nothing about the rules of the Pact of the Tome feature explicitly identifies the Book of Shadows as a spellbook, so items that refer to a spellbook's functionality won't work with it.

Specifically in the case of the spellshard's wording, a feature would have to say you use of a book works "like a Wizard" to qualify. Notably, the Ritual Caster feat does not have that wording, so RAW, it wouldn't work for that either.