Is it clear to define a class’s Spellcasting Ability when they are not spellcasters?

Question

For a homebrew project, I have a feature that is magical, but not spellcasting per se (it does not involve spell slots, its effects cannot be targeted by counterspell or dispel magic, etc.). I want to define its save DC and “spell” attack, and it seems to me best to just define a “Spellcasting Ability” per se rather than defining some other ability used for some other kind of non-spell magical attack. It just seems more consistent, and potentially allows the class to automatically benefit from magic items that boost spell save DC and/or spell attack (they won’t be able to attune most such items but I think there are some they can). I also like that it has the side-benefit of allowing a few edge cases to use this Spellcasting Ability instead of the default none.

This is the text I have at the moment, with the ability’s name replaced by ~:

Spellcasting Ability

Though you are not a spellcaster, ~ can have magical effects that call for a saving throw or spell attack. You use your Charisma whenever a feature or effect refers to your spellcasting ability. In addition, you use your Charisma modifier when setting the saving throw DC for your ~ and when making a spell attack as part of a ~:

Spell save DC = 8 + your proficiency bonus + your Charisma

Spell attack modifier = your proficiency bonus + your Charisma

Is this clear? Does it cause any breaking edge cases? The “~” can call for weapon attacks or spell attacks; is this likely to cause any confusion? All saving throw DCs would be calculated as above; does that cause any confusion relative to the previous statement?

Answer 1

I think it does less than you think

Let's try to run through the different concerns:

Magic Items

You're right that most spellcasting buffing items aren't applicable due to attunement restrictions. However the remaining ones don't actually care about you having a spellcasting ability, merely that you're making a spell attack:

While holding [this magic quarterstaff], you gain a +1 bonus to spell attack rolls.

— Skyblinder Staff, Guildmasters' Guide to Ravnica

And there are (to my knowledge) no items which would be eligible to boost your DC and the templating wouldn't work in your favour, as the items boost the DC for the spells themselves, not a number in general:

you gain a bonus to the spell attack rolls and the saving throw DCs of your [class] spells.

Spells and spell attacks

Spells and spell attacks are on some level independent. While obviously most spell attacks are part of spells (and thus have a defined ability through the spell granting feature) there are exceptions. Most of those exceptions are on monsters and thus aren't super relevant. The most clear PC option here is the Sun Soul monk, which gets a spell attack it can make using it's Dexterity.

Now there's nothing here which is an issue for your proposed rule, but my point is that a spell attack having an associated ability is not automatically covered by having a defined "spellcasting ability". You might want to reorder the two sentences, as defining your DC and spell attack modifier is the always relevant line, while defining a spellcasting ability is more incidental and covering for oversights or odd interactions. Though obviously if any ~ or other relevant features grant spells, having a defined spellcasting ability is important.

The places where a character would use a none-spellcasting ability is when the feature which grants spells doesn't define an ability (as is the case for the Totem Warrior).

Also note that it's quite possible for a character to have more than one spellcasting ability (each spell should have one associated with it though) via racial spells, multiclassing or feats like Magic Initiate. Incidentally, I think your current phrasing could be read to override the spellcasting ability of other of other sources, which is presumably unintended and would be an issue in particular for multiclassing.

Confusion

I realistically don't think defining a spellcasting ability would cause much direct confusion. I've seen monks referred to as having wisdom as their spellcasting ability, so if anything you're leaning into shorthand. What I'd worry about is if you're having options in a list which interchangeably grants weapon attacks using Strength or Dexterity and spell attacks using Charisma, you're sowing the seeds for someone to missing what ability a given attack uses. It'll probably read more easily (requiring less mental overhead) if each ~ simply said which ability a given attack uses (though you could handle that with reminder text if you're so inclined). All DC's being set by Charisma should be fine, that's fairly normal. Arguably common enough that it'll read well without actually being defined.