Who can create copies of spells that can subsequently be copied into spellbooks, etc?

Question

Character A finds a spell written on a wall and copies it. He takes the copy to character B who copies it into her spellbook or Book of Shadows for her future use. Assume the spell is one B can prepare and use. Character B is a wizard, a tome warlock, or has the ritual caster feat.

What must be true about A for this to be possible?

The best answer will cite sources and cover multiple cases with a simple TL;DR.

Answer 1

Wizards are described as only being able to copy Wizard spells in the spellbook sidebar, and the available sources only appear to be one of four locations:

1. A spell in another caster's spellbook
2. A spell on a scroll
3. A spell in your own spellbook (reduced cost)
4. A spell you currently have prepared (reduced cost)

Nevertheless, you're still restricted to Wizard spells in your Wizard spell book. You couldn't add cure wounds to your Wizard spellbook, even if you were a Bard, had the spell prepared, found a scroll for the spell, or even somehow found a spellbook with cure wounds in it.

Furthermore, you can only copy spells into your spellbook, not in small part due to the fact that copying a spell is synonymous with understanding and learning to cast a spell. If you cannot do the latter (because the spell isn't one you can learn) then you certainly cannot do the former.

As I've mentioned above, I consider "spellbook" to be primarily a description rather than an actual specific object. The cost difference between "book" and "spellbook" in the PHB isn't justified anywhere, but to me it reads merely as a quality and size distinction. A "book" can be any book of any length with any quality. It could be a 20 page pocket prayer manual on unbleached papyrus, gut-bound to a wooden shingle. A "spellbook" is high quality book (leather bound with vellum pages) that's large enough to hold 100 pages of spells.

Thus, when you say, "the book has the fireball spell in it" you've already determined that its a spellbook. If you find a book that is not high quality that contains a written spell on it in spellbook format, it would not be useful and you would say, "the book describes the fireball spell, but as you study it you find it is imperfect and lacks vital details that have been lost due to the quality of the manuscript."

Similarly, a Wizard spell copied by a non-Wizard would be useless. It would lack the meaning and detail that the original caster needed to prepare the spell, and any other caster studying the work would not have enough information to translate the spell and copy it into their own spellbook.

On the other hand, if you attempt to copy a spell without meeting the proper requirements (having the spell on your class spell list, spending the time and the inks, using a book of sufficient quality) then you can't use the copy to prepare the spell. That tells me it's fundamentally incomplete and, therefore, not a copy and then also not a spell in a spellbook. Therefore, "copy a spell" and "add a spell to one of my spellbooks" are also synonymous terms.

A Warlock would similarly only be able to copy any Ritual spell he or she finds into his or her Book of Shadows from similar sources. A character with the Ritual Caster feat would only be able to copy ritual spells of the class he or she selected when choosing the feat.

Answer 2

1. Character A is a Wizard and copies the Wizard spell into her spellbook which she brings to Character B so that he can copy the spell into his spellbook. The spell must be of a level for which both Wizards have slots.
2. Character A is a Warlock with a Book of Ancient Secrets who copies the Wizard ritual into her Book which she brings to Character B so that he can copy the spell into his spellbook. The spell must be equal to or less than half of her Warlock level (rounded up). The spell must be of a level for which the Wizard has slots.
3. Character A has the Ritual Caster feat and copies the Wizard ritual into her ritual book which she brings to Character B so that he can copy the spell into his spellbook. The spell must be equal to or less than half of her total level (rounded up). The spell must be on the spell list that she picked when she acquired the feat. The spell must be of a level for which the Wizard has slots.

Copying a spell into a spellbook (PHB 114), the Book of Ancient Secrets (PHB 110), or a ritual book (PHB 169) takes 2 hours per level of the spell and costs 50 go per level. Because there are 2 copies in this example, you would double the time and cost, so that even a 1st level ritual will take 4 hours and 100 gp.

4. There is another option (XGtE 133), but it is highly impractical. Character A can scribe a spell scroll. However, she must be proficient in the Arcana skill, provide the material components of the spell, must have the spell prepared (DM could houserule preparing it from the wall or she must have first copied it into her spellbook to prepare it; either way this should require her to be a Wizard*), and then must pay the time and cost to create the scroll. 1 day/25 gp for 1st level, 3 days/250 gp for 2nd level, and increasing somewhat exponentially. Also note that there is a chance of failure with this option as well where the scroll would be destroyed during the attempt (Intelligence(Arcana) vs 10+spell level DC (DMG 200)).

*I believe that Character A cannot be a Warlock to scribe this spell because they cannot prepare the spell from their Book, only cast it as a ritual. This is also true for those with the ritual casting feat. Among arcane casters, only Wizards can prepare spells that they don't know. Divine casters also don't really know any spells - they can prepare a small number of spells out of a large list of spells available to them.