One of my players (a Forge Cleric - though I'm not sure that it matters) wants to be able to craft useful magical items, as the campaign goes on, rather than merely mundane equipment that's easily available by other means. Crafting is a big part of his character backstory and I like to be a permissive DM whenever possible.

I intend to allow them some flexibility to craft magical items while sticking fairly closely to all of the crafting rules as laid out in this excellent answer by Xirema to a related question. My players will shortly hit level six, when according to the DMG they become capable of crafting Rare items.

In my game, in terms of how many items I usually hand out to my players, I stick pretty close to Xanathar's guidance on item distribution (as found in the Magic Items Awarded by Rarity table, specifically), with a little bit of leniency to account for the fact that my group has 6ish players rather than the average usual 3-5.

If I allow my player to craft additional magical items how can I maintain game balance?

• Reduce the number of items that my players can acquire by other means? This seems to punish the other players.


• Make encounters more difficult than normal to account for my party possessing a higher than usual number of magic items? Doesn't that just negate the reward?


• Or, am I overthinking this and will 5e's bounded accuracy, and each player being limited to three attunement slots, largely take care of any issues for me?

Please back answers up with your own experience in a comparable situation.

Increase the difficulty if needed

I have ample experience in very high magic campaigns, including the buying and crafting of magic items, and the best solution I've found is to just make the challenges more difficult. This way, you maintain the level of difficulty that your table wants to experience.

Doesn't that just negate the reward?

In my experience, it doesn't. When characters acquire magic items they are ready for more difficult challenges. This, in itself, is its own reward. The players can recognize that their effort to collect useful magic items has paid off in their ability to complete more difficult challenges (and collect the rewards of such challenges, whether it be monetary or story rewards).

On the other hand, I have had some (albeit considerably less) player groups who do want an "easy mode" after they spend considerable effort compiling their perfect item set. In these groups, you may want to give them a few sessions where they can stomp through the challenges they were preparing for. Then, when they realize their new power level, you can introduce plot hooks for more difficult challenges.

I think the premise of your question overlooks a pretty substantial issue:

It's actually kind of hard to craft magical items

Even when using the more flexible, less expensive rules provided by Xanathar's Guide to Everything, crafting Magical Items is prohibitively difficult for players, greatly reducing the risk that they could overpower their campaign by crafting tons of magic items. The only real way for players to abuse this system is with a complicit DM.

Cost

The cost of crafting a Rare quality item is 2000gp, plus 10 work-weeks of effort (XGE, pg. 128-129). Ten work-weeks is a substantial amount of time, nearly 3 months. Now, as DM, I make a substantial effort to provide Downtime moments for the campaign relatively frequently, but even by those standards, it would take a character probably 15-20 sessions to successfully craft a single Rare-quality Magic Item. Multiple Party Members (each with the requisite Proficiencies) would be able to collaborate to dramatically lower that time; but that also means they're not doing anything else during their downtime.

And on top of that, 2000gp is not a huge quantity of money for a level 6 party (at an average of 88gp per CR5-10 encounter, DMG pg. 133, it would take roughly 23 random encounters for the party to acquire that much gold), but it is enough that the character probably isn't getting that money without their party members forgoing their share of the adventuring rewards. And bear in mind that that cost is an abstraction: both the DMG and XGE suggest and encourage the idea that crafting Magic Items should involve acquiring rare components (through purchase or adventuring) that mean simply acquiring the gold is insufficient.

Xanathar's Guide to Everything has the following suggestion on how difficult it might be to acquire the necessary ingredients:

An item invariably requires an exotic material to complete it. This material can range from the skin of a yeti to a vial of water taken from a whirlpool on the Elemental Plane of Water. Finding that material should take place as part of an adventure.

The Magic Item Ingredients table suggests the challenge rating of a creature that the characters need to face to acquire the materials for an item. Note that facing a creature does not necessarily mean that the characters must collect items from its corpse. Rather, the creature might guard a location or a resource that the characters need access to.
beginarrayl
hline
textMagic Item Ingredients \ hline
textItem Rarity & textCR Range \ hline
textCommon & text1—3 \ hline
textUncommon & text4—8 \ hline
textRare & text9—12 \ hline
textVery rare & text13—18 \ hline
textLegendary & text19+ \ hline
endarray

If appropriate, pick a monster or a location that is a thematic fit for the item to be crafted. For example, creating mariner's armor might require the essence of a water weird. Crafting a staff of charming might require the cooperation of a specific arcanaloth, who will help only if the characters complete a task for it. Making a staff of power might hinge on acquiring a piece of an ancient stone that was once touched by the god of magic—a stone now guarded by a suspicious androsphinx.

—Crafting an Item, Xanathar's Guide to Everything, pg. 128

It should be quite obvious that a level 6 party can plausibly acquire items from a CR9-12 scenario, but it will be quite difficult and potentially deadly.

So the reality is that if a character has the money/time/ingredients to craft a good magic item, it's because the rest of the party is collaborating to make it happen, whether or not they're literally doing so as part of the creation process. And if so, I don't really see the problem: D&D is, first and foremost, about collaborative storytelling, and if the players are all working in concert towards a specific goal, well... Mission accomplished.

Magic Items require a Recipe

The other major block to player characters crafting their own Magic Items is the fact that items require a recipe to be successfully crafted. There's plenty of characters that would want to craft a bunch of Belt of Hill Giant's Strength to hand out to their fellow players, but they first need to research/learn the recipe for crafting such a belt, and as DM, you have control over how long it takes to even learn that recipe.

And then they successfully learn that recipe: great! If they want to spend the time to start mass producing that item, they're only limited by how much gold and downtime you give them (again within your control); but they can only make that one type of item, and if they want to make something else, they need to learn how to make those other items.

So there are definitely scenarios where players might be able to craft lots of magic items... all of the same kind, where there's no guarantee that doing so will represent a substantial power boost for every character. 21 Strength is nice, but the Sorcerer still doesn't have Greatsword proficiency, nor do they have a very high Armor Class, so they'll still get stomped if they try to fight in melee combat.

Crafting items that every single party member can benefit from means having recipes for every single kind of item, and you have all the power in the world in deciding how easy or hard it is to get those recipes.

On the other hand: Uncommon and Common items

Setting aside the recipe issue, it's worth mentioning that Uncommon and Common quality items are substantially easier to make, requiring only 2 and 1 workweeks of work respectively, only 200gp and 50gp respectively, and requiring ingredients from far easier encounters. Clearly, if a character wants to fabricate items at this rarity, they'll have a far easier time of it.

By the standards laid out previously, there is a genuine chance that characters could acquire a very high quantity of Uncommon or Common quality Magic Items by efficient use of Downtime.

But here's the trick:

Uncommon quality items.... just aren't that good.

At least not once you're level 6.

Most Uncommon quality items are +1 weapons or items that are of comparable power. A +1 weapon is nice, especially since it counters the resistances of particularly tough creatures, but in most scenarios, it just represents a roughly 10% improvement to overall damage output. That's good, but it's not "break the campaign" good. Same for items like the Bracers of Archery, which are a +2 to damage but with no increase for attack rolls, which again averages out to a roughly 10-15% damage improvement (assuming the character was already optimizing for damage). Again: very nice, but hardly something that will break the campaign.

Other items, like Adamantine Armor, represent a 5-10% reduction in damage, A Shield +1 or a Cloak of Protection represents another ~10% reduction, but again: not quite game-breaking.

And just so it doesn't go unstated: Common quality items barely factor into this discussion, because the effects they have on combat are often pretty minimal.

If a character stacks as many Uncommon-quality items as they can without surpassing Attunement limits, they can expect to have as much as a +30-50% damage output improvement or (because of attunement limits) +20-30% damage input reduction, which is quite substantial; but this implies that they perfectly roll every single item they need to perfectly optimize, AND that they're given way more than enough time and money to successfully craft or acquire said items, which by the standards I've set above (especially given the issue of finding recipes for various items), that's incredibly difficult to accomplish with a single character crafting magic items, especially since they would need to have tool proficiencies for each different category of magic item they wanted to craft.

All for a 50% improvement to damage output and a 30% reduction to damage input, which basically just puts them on par with a character a few levels higher than them.

Considerations like this are why, at my table, if characters are a whole tier ahead of where they need to be to craft certain kinds of magic items, I'm often willing to just let them buy the items they need (for an appropriately expensive quantity of gold, of course)—so at level 6, they're allowed to buy Common or Uncommon quality items; at level 11, they can buy Rare items, and so on. Because like I said: these items just aren't that powerful, and for the amount of gold that they would cost, I've not seen problems with characters becoming overpowered just from having access to items of this quality.

I do think you could run into problems if these same characters could instead arbitrarily equip themselves with lots of Rare-quality items, since those items do represent a quite substantial increase in power, but as established, it's far harder to mass-produce such items.

Conclusion

Concerns about oversaturation of Magic Items, especially when faced with a character that can craft them themselves, are valid, but they need to be tempered with the fact that as DM, you have a lot of control over how many items they can produce, or which items they can produce, hewing to the basic constraints set by the rules in the Dungeon Master's Guide and Xanathar's Guide to Everything.

A Forge Cleric gains proficiency in Smith's Tools, and from the sound of things, they probably have a few more Tool Proficiencies that allow them to create other kinds of Magic Items. That'll offer a substantial variety, but it'll hardly encompass the range of items that can be crafted, and given that there are 17 kinds of Artisan's Tools in the game, the 3 or 4 proficiencies they could plausibly have at level 6 simply will not span the whole gamut of items they could possibly want to make.

So facilitate the Cleric's attempts to learn Magic Item Recipes, and I think that if you follow the guidelines provided by these sourcebooks, you'll find that there's simply not much risk of the party becoming overpowered.

There's a few answers to this that all sort of interlock.

Yes, reduce the number of awarded magical items.

You don't need to be super strict about the item count, but if your forge cleric really wants to be a crafter, that's their fun, so you probably should play into that theme and make the PC a major source of items rather than presenting them in treasure hordes.

Reduce the number of random magic items they find, or at least pull down the level of them -- instead of finding a rare and several uncommons, maybe they find a couple uncommons and a several commons.

The common items in Xanathar's Guide (and other items you might invent along the same power level lines) can make it feel like the party is collecting cool magical stuff while not actually raising their power in a meaningful way.

You control which items are available for crafting.

The DMG is pretty clear that you get to tell the player yes or no (or better yet, "yes, and") for any magic item they're looking to build. They have to locate the formula or schema for building the item -- which might be provided by divine inspiration in this case -- and you're free to declare specific items or locations involved in the creation process.

Here's what I would do in your situation:

When the PCs kill a particularly powerful monster or NPC that would otherwise have some Rare+ items in its horde, instead they obtain a magically powerful ingredient. It might might be a part of the monster they just took down (like taking a troll's heart or a dragon's largest fang after you slay it), an object in the horde that has innate power (a chunk of adamant ore, a shimmering crystal shard, a potted bloodvine plant, a mandrake root preserved in salt from a widow's tears), or a preserved monster part (a dried rakshasa paw, a phial of angel's blood, a mummified imp, a gorgon's eye sealed in lucite), whatever seems flavorful to you.

The Cleric gets a moment of divine enlightenment that clues him in on what the item is and what it might be used for -- essentially giving him a list of two to four items that this particular ingredient might be used to empower. So he can't just build any-old-thing at any time, but he can make some choices about what to make and who to make it for (including, for example, choosing what kind of weapon to make when there's a choice), and if he really wants a particular item, you can work with the player to come up with what sort of ingredient they need to locate, with appropriate adventures attached.

Don't worry about it too much.

Even if you go overboard and let the party have too many items, it isn't that bad. The game tends to self-correct; the player characters have limits on how many strong items they can use due to the attunement rules; and if they get too strong it just means they level up faster and start fighting tougher monsters that bring it all back into balance.

Having a bag full of magic stuff they aren't really using is a good opportunity to let them trade away some of it for favors or other benefits, or they can have some NPC companions who would like to use those items even if the PCs have better stuff.

The forge cleric's ability is obviously a feature of the archetype, and should provide some benefit, just like other more combat oriented features of other archetypes. Diminishing it by increasing encounter difficulty or reducing awarded treasure is unfair if you would not do that for any feature of another class/archetype. So, it should certainly be allowed with minimal interference. However, as the character is asking to change the class - making a class feature more powerful - by allowing the creation of magical items instead of simply mundane items, you would be well advised to compensate using any of the means that you suggest.

However, since this is a change that you and your player are working on and is completely homebrew, might I suggest a method of implementation that would minimize the amount of tweaking you would have to make to the campaign while still maximizing player agency?

Instead of changing Artisan's Blessing to allow wholesale creation of magical items, limit its creation of magical items to require magical starting materials (so, mundane materials = mundane item, magical materials = magical item). The 100 gold limit on the item's value is still a problem for most magical items (especially the rare ones the player wishes to create), but that might be relaxed for this particular use.

In a nutshell, the modified ability would allow the cleric to reforge an existing magic item into a different magic item of equivalent value (varying by up to 100 gold in value, which is covered with the supplied mundane materials per the normal feature). You could further restrict that the new magic item must be of a similar type to the old (armor to armor, or even chain mail to chain mail) and the resultant item would still require metal be used in its construction (as required by the mundane version of the feature).

This therefore does not change the magic item economy of the campaign in a way significant enough to require balance changes, but still allows the cleric to increase the party's effectiveness by increasing the utility of obtained magic items.

Possible exploits include incrementally increasing the value of a given magic item by reforging it multiple times. But, since the rarity of a magic item is still capped (at rare for level 6), this isn't likely to be unbalancing considering that the frequency is still limited by Channel Divinity uses (2/day at 6th) and the overall power level is theoretically similar between items in the same tier (it's not, but since you control the gold value of magic items, you can adjust for this). In fact, since magic item prices are not explicitly stated in any official publication (though look here for a good table to use), you could simply allow any magic item to simply be reforged into another magic item of the same rarity, eschewing the gold piece part of the equation. In this case, I would still require a flat 100 gold worth of mundane materials for each reforging just so that there is still a significant (though not insurmountable at 6th level) non-renewable cost to the reforging.

Lastly, as with all things, each reforging should be looked over with a critical eye. Let your player know up front that you reserve the right to veto any planned reforge if you feel the resulting item could negatively impact your campaign or otherwise makes no sense (like reforging consumables in most cases).

As mentioned elsewhere, crafting takes a long time, even with an alternate rulesset that reduces the time taken. It's unlikely to be a problem unless you have large swathes of downtime and lot and lots of money.

That said, if you're content to allow them to create additional items, but you're concerned about it causing a magic item economy issue.

Limited use and/or Attunement

Attunement is 5e's natural mechanism for limiting Magic Item use. You get three slots, choose them wisely.

In my games, when I want to give out extra magical loot, but I'm concerned about going over the limits, I give the items uses. Maybe it's a potion, a throwable, a scroll, or it's

a weathered, leather-bound notebook with an old quill pen that never seems to run out of ink. Only three pages remain within the notebook; the rest have been torn out. Burned into the front cover are the words "Write and rip to place the item within your grip. Something new or something old; something less than a pound of gold".

Plot Crafting

It's worth noting that you could have story elements that require a "master craftsman" or "we need to make the MacGuffin". I've never done that with this specific circumstance (a crafting character), but I've used the same effect for other character specialties (Expert Performers, or Sailors, or the like).

Or just reduce to the loot you give and let the crafting shore up the difference

I know you said you wanted to avoid feeling like the creator of a quantum ogre. So, this is partially for some 3rd party reader, partially just saying what I would do, and partially trying to change your mind.

Maybe this is a fundamental difference between us as DMs, but I am 100% willing to secretly mislead my players so that they feel like their decisions are important (or fabricate scenarios to the same effect). I love doing it with Trinkets: "You step into the hazy bauble shop and speak to the elderly gypsy behind the counter. After a few moments of conversation, your catches her eye and she asks you where you got it."

The players don't know what they don't know. At the end of the day, it's about everyone having a good time. If this method would detract from your table's (yours included), then that doesn't work for your table.

The conditions whose combination makes the problem impossible to solve are:

1. Everyone gets magic items of similar value by default


2. A player can craft powerful magic items


3. without significant costs


4. And use them for themselves

So the solution is to relax some of the restrictions.

1

You've said that you don't want to reduce the number of magic items the players get; but perhaps some of the magic items could be acquired by crafting, instead of simply looting or buying them. The same way a cleric heals the party, they could instead craft items for the party.

2

Sometimes, it's more about flavour than power. You could allow some minor enchantments that don't skew the balance too much; or, if you randomly generate loot, you could allow specific magic items to be crafted. Crafting consumables, especially if they consume spell slots, or merging magic items (be careful about attunement slots) could also work.

3

Typically, there are three ways: gold, quests, xp.

The gold one depends on your campaign actually using gold for something: for example, one of my players bought a shop, while another player got a better sword. Both are happy with their choice and can see the fairness of it.

Quests is a bit tricky, especially as the party might not want to go for a quest. If they do, just to help the crafter, it's still someone getting more items than others for equal contributions. Perhaps if only the crafter goes on a quest so they consume resources; or maybe the others get bonus XP for being helpful.

Which brings us to XP. It doesn't have to be a sacrifice, although note that "everyone gets 1000 XP and you get special ingredient X" is pretty much equivalent to "you lose 1000 XP to get the ingredient", rationally speaking. I'm quite fond of this, as it can be used to balance things; the crafter gains some powers but is a bit lower level to compensate. Of course there's no set ratio of XP to gold (and the magic item prices are messed up), but I usually go for 2 XP for 1 gp and follow the Sane Magic Item prices from GitP (based on some frivolous attempt to simulate a level using magic items).

The beauty of this is that you can make the trade voluntary and reversible, therefore if the player doesn't like it, they can fix it themselves.

4

Similar to 1, if everyone gets more magic items, everyone is happy. Perhaps you'll have to boost the difficulty of the encounters a bit; but you do that when they level up as well, right?

Overall

The sad thing is that there's no support for advancement through magic items. Although you could camouflage class features as magic items, but that's a bit lame.

What I do in my games is a mix of all of the above: I have some value for gold (can even hire tutors for XP), I lower the number of magic items found, require some XP sacrifices, and focus on minor adjustments and customisations. It is not bulletproof, but I'm not publishing a system that will be played widely; in a single table, the randomness of a d20 offsets going from a +1 to a +2.