I made a homebrew item for possible inclusion in our campaign (I'm not the DM), which I thought was neat enough to publish for the community:

 My concern is whether the item is too OP for common rarity. I'd figured that an item able to cast a single 1st-level spell just once a day is fine, but does the spell-storage ability make it too versatile? An uncommon spell-storing item would make sense to store 3 levels worth of spells, based on existing items in the DMG, but it made more sense to me for a Locket to only hold 1 spell inside it. I did give it the capability to downconvert an upcast 1st-level spell back to 1st level when stored, so I can see that being extra handy for Warlocks, for example.

Any thoughts/suggestions? Could the description be clearer? Would you want to use it in your own campaign? Thanks in advance :)

Edit: I should probably give the link: Spell Locket

Quote from naruhoodie >>

My concern is whether the item is too OP for common rarity. I'd figured that an item able to cast a single 1st-level spell just once a day is fine, but does the spell-storage ability make it too versatile? An uncommon spell-storing item would make sense to store 3 levels worth of spells, based on existing items in the DMG, but it made more sense to me for a Locket to only hold 1 spell inside it.

If you take a look at Belt of Giant Strength, there are multiple versions at the same rarity of different strengths, so I think it'd be perfectly reasonable to have a less powerful item at Uncommon rarity, to reflect that it's magical.

After all, when it comes to magic items it's ultimately up to the DM when (or if) you obtain it, and what it will cost; a DM can just make it a cheaper item, or with it being a locket you could wear it in addition to another spell-storing item. So yeah, I think it would be fine as an Uncommon item.

I don’t think that’s too powerful for a Common item as long as you put a couple restrictions on it. Like, once the spell is cast from the locket it disappears and the locket needs to be refilled before it can be used again.

I would use it in a campaign.

Basically it's a less-powerful Ring of Spell Storing which is a Rare item and stores up to 5th level spells. So, I could see 3rd level being Uncommon (like a Pearl of Power although it works a bit differently, recovering slots instead of storing spells) and so a 1st level would be fine as Common. Assuming, of course, the spell is used and gone from the locket.

If you take a look at some other Common magic items their magical/unique effects are all pretty minor, like never getting dirty, self-mending clothes, that kind of thing.

I feel like being able to use a spell of any kind puts it beyond Common, even if it's just a single 1st-level spell. There's plenty of variance in the strength of items within each rarity, so the locket being Uncommon doesn't mean it has to be priced like other Uncommon items, but it seems too magical for Common.

If a DM wants to potentially offer it as a reward though, then they'll either just choose to give it, or have to integrate it into a list themselves, so they're free to make it more likely to be rolled as a neat little early level magic item. For example, if the locket doesn't have a spell within it, then it could be easy for a merchant to think it inert and non-magical and sell it as such.

The DMG specifically states that magic items capable of casting a single Cantrip or 1st-level spell are “common.”

 Magic Item Power by Rarity

Maximum Spell Level. This column of the table indicates the highest-level spell effect the item should confer, in the form of a once-per-day or similarly limited property. For example, a common item might confer the benefit of a 1st-level spell once per day (or just once, if it’s consumable). A rare, very rare, or legendary item might allow its possessor to cast a lower-level spell more frequently.

Yeah, if there was such thing as "Major Common" rarity, it'd definitely fit there. But it does only allow casting from the locket once a day, and you can only cast a spell into the locket when it's open, after which it can't be opened except by casting the spell out of it. So no putting a different spell in until the next day, if you already used it today.

It also requires being able to "tap" the locket to release the spell, which means you need a free hand (or careful precision using the pommel of your weapon.)

I could certainly see a merchant having one that doesn't contain a spell and assuming it's just a normal locket, or even a commoner using it to hold a lock of hair or little trinket with no idea of what it's capable of :) Especially if it'd been in the hands of a possessive mage who cast Arcanist's Magic Aura to hide the fact that it's magic.

I've made some changes to the description, how does this sound? (The changed/added parts are underlinedboldface.)

If you restrict the locket to only holding 1st-level spells with a casting time of 1 Action, Bonus Action, or Reaction, then that would eliminate the need entirely for “If the locket is closed before the spell's casting time has completed, the spell fails and is lost.”

I actually added that to go along with the flavor of a locket, where you could say there's a glow or fog or something coming from the opened locket as the spell is being cast, and closing the locket shuts off the glow/fog (and the spell.)

I don't want to restrict it to spells with single-turn casting times. But I also don't want to specifically say "the opened locket glows while the spell is being cast" so that people can flavor it however they like.

In any case, I added that since I thought it made the locket a bit more interesting. Of course any spell with a casting time longer than 1 turn is effectively being concentrated on (according to the D&D spellcasting rules), so the player failing a CONcentration save during the casting would also make the spell fail. This just adds another route for that to occur.

Edit: Looks like I was confused about the Spellcasting Rules. I'd assumed that a spell interrupted during its casting time was lost along with the spell slot, but it actually isn't!

Now I just need to decide whether interrupting the locket spell's casting will cause it to be lost anyway, or whether it closes itself back up and still contains the spell. (The open/close aspect of the locket adds a layer of complexity you don't get with rings...)