Do magic staves require the wielder to have the spells on their list in order to cast them?

Question

All of the magic staves in the 5E DMG simply state that the wielder can use an action and expend 1 or more of its charges to cast one of the spells from it. Literally none of them require the spell to be on the caster's spell list.

But a few of the magic staves from the Lost Mines of Phandelver--the Staff of Defense and the Spider Staff--specifically say "if the spell is on your class's spell list"...is this a typo? A new addition to the rules on magic staves? Or just something specific to these particular staves (for some unknown reason)?

Answer 1

This is a specific case that overrides the general one

Firstly, on PHB, p. 7:

Specific Beats General

This book contains rules, especially in parts 2 and 3, that govern how the game plays. That said, many racial traits, class features, spells, magic items, monster abilities, and other game elements break the general rules in some way, creating an exception to how the rest of the game works. Remember this: If a specific rule contradicts a general rule, the specific rule wins.

Generally speaking, magic staves (and other magic items) that allow you to cast spells, usually "once per long rest" or "once per dawn", or through the use of expending charges, do not require that you have those spells in your spell list.

The Staff of Defense and Spider Staff, however, both override that by stating "if the spell is on your class's spell list" (LMoP, p. 53), as you note. Therefore, these staves do require that you have access to these spells already, which is different to other magic items that allow the casting of spells.

As @V2Blast points out, the Starter Set came out before the PHB or DMG were released, so such design conventions had likely not been finalized/refined at the time of its release. It may be that these are different from the items in the DMG because they decided to change how such restrictions were implemented, using attunement requirements rather than requiring you to already have access to the spells that a magic item provides.

Answer 2

There is no general rule that requires you to have a spell on your class list to be able to cast it from a staff or other magical item

Neither the description of staves specifically, nor the general rules about casting spells from an item, mention any requirement that a character must have access to a spell from their class to be able to cast it from an item. It's been a few years since LMoP was written, and if that was intended to be a general change it would have made its way into errata by now. Similarly, if it is an error in LMoP, it's an obvious enough one that it should likewise have been corrected. These staves simply have specific rules that require the user to have access to the spells they can produce.

However, it might be notable that all of the staves in the DMG that can cast spells require attunement by a character that is already a thematically appropriate spellcaster (though the spells granted/class-available don't perfectly match in many cases). If I were to hazard a guess, I'd reckon that the staves in LMoP might have been designed slightly differently so that they are still beneficial to a character who is not an appropriate spellcaster, since anyone can attune to them and get some kind of bonus, but can only be fully utilised by the right kind of spellcaster.