I let one of my characters use this spell to repair physical damage from a monster shoving a sword through a Warforged npc. I let them patch up it’s wound from bleeding but didn’t heal any of its hp because it’s not a healing spell. Is this an acceptable usage of this spell for future sessions?

Mending is ofton used to heal Constructs as seen for example with the steel defender from the battle smith Artificer subclass: https://www.dndbeyond.com/classes/artificer#BattleSmith

So this is a acceptable and even common usecase, as Constructs cant be healed by normal hesling spells in most cases.

Next question is if your Warforged is a Construct or Creature.

As it bleeds its most likely a Creature but Mending can still be used for flavour.

Though you need to allow normal healing in that case as otherwise it couldnt be healed (which you stated but just wanted to point it out).

Prestidigitation to clean out rust, mending to repair the holes left behind.

Since the spell doesn't specify that the repaired object needs to be nonmagical, this could be used to fix a tear in reality if we regard reality as an object and thus you could theoretically use mending to remove a Blade of Disaster, as the spell specifies that it is a "rift" which i would say is synonymous with break.

tldr: use mending to mend all your planar rifts

It does state it can’t fix anything magical it can only fix physical breaks. A planar rift can be classified as magical soooo

Quote from Riesenfriese >>

@GHSkub LODEstones, not LOADstone. A lodestone is just a naturally ocurring magnet. Id price them at a silver coin each.

 It's LeviOsa, not LeviosA

Maybe not. I would say that oozes and rust monsters dissolve the material rather than break it in two. The iron is separated into millions of tiny pieces. But if you had a source of raw material ready from another sword, maybe? Maybe that's enough of a difference to warrant a completely different spell, maybe 1st or 2nd level, that is known primarily by artificers.

Certainly, there are rules for magic item creation in the DMG and Xanathars/Tashas. You spend gold equal to a similarl magic item level, (probally common like 500gp maybe) the materials for the item, (1/2 cost in equipment table) and the components to cast the spell daily on the item for weeks, months, or a year (some components have a GP cost others are up to).

If I cut open an apple, put nails in it, and then cast Mending, I should be able to seal the apple back up without forcing the nails out, right?

Can mending be used to heal a warforged?

one use i've found for this which may or may not work depending on whether your DM rules individual cells as objects or as creatures. but perhaps you can use this spell to close wounds in a way that doesn't necessarily heal them, but does still close them, leaving a bruise. this application of the spell would almost certainly require a medicine check, but given the way the spell is written, it doesn't explicitly state this can't be a use of the spell, even if it is written in a way that means you have to argue for cells being objects rather than creatures

Theoretically would this work on living tissue (primarily since it doesn't say you can't)?

If I took a loaf of bread, cut out the middle, then cast mending, how would this "repair" the bread? Would it make new bread or would it bind the two end pieces together? or would it not work at all?

Took this on a Bard, to repair instruments / broken strings. :)

Could Mending be used on food? Eat half a steak and use Mending on it? Eat some more , repeat the process till everyone is full.

I know it has been 5 years, but still: an arcane focus can replace those lodestones without any additional cost, so...

A lodestone is just a kind of magnetic stone. Its not 

@MatthewNuckles and @Mirel After reading your questions, I looked on reddit, and someone had what I consider a decent point: it's a transmutation cantrip, not a conjuration cantrip. In this case, since you don't have the major broken/torn pieces, you probably wouldn't be able to make infinite bread/steak and it will likely not work (though you can certainly try).

Quote from DnDDetective >>

One thing that people overlook about Mending is its casting time. Because of the spellcasting rules (per the PHB) you would lose any concentration you have active when you cast it (because it takes longer than an action to cast).

Longer Casting Times

Certain spells (including spells cast as rituals) require more time to cast: minutes or even hours. When you cast a spell with a casting time longer than a single action or reaction, you must spend your action each turn casting the spell, and you must maintain your concentration while you do so. If your concentration is broken, the spell fails, but you don't expend a spell slot. If you want to try casting the spell again, you must start over.

 

 The Lyre of Building makes Mending an action, which is a cute trimmer for its other abilities.