Equipment Design (5e Guideline)
From D&D Wiki
5e Equipment Design Guide
Have you ever felt like you creating an item to highlight a unique idea or concept, but were unsure of how to create a piece of equipment? Well, you're in luck, because this guideline is a good place to start, as it should help cover how to create most types of equipment in 5e. As with everything on the wiki, please make sure that you are familiar with the precedent, which in this case for items is set by the 5th edition corebooks, the Player's Handbook, (PHB) and Dungeon Master's Guide, (DMG). Explicit guidelines for creating a magical item are provided on 5e DMG pp. 284-5.
Naming Your Item
Creating A Unique Item
Items come in all shapes and sizes and can have effects as varied as making a flying death machine to changing your outfit at will. When creating an item, ask yourself, has a similar item to this already been made by WotC(see 5e DMG pp. 150-214/5e SRD) and do a quick search on the wiki's relevant equipment section to see whether there is an already existing item that is similar to what you are trying to create.
Mundane items should be able to be used by all characters. They should not have class, race, or background requirements and they should not provide additional features for being a certain class, race, background.
- Mundane Item Description
Adding a description to nonmagical items is essential to understanding what the item looks like. Everyone is not going to know what exactly you mean when you call an item a katana, even if the name fits the item you are creating.
Realistically, changing the cost of mundane weapons does not affect how balanced the item would be, though if an item does have a gold cost that falls too out of line of the standard gold cost for mundane weapons, it likely needs to be adjusted. Weapons should, however, usually have a gold cost similar to its weapon counterpart if it has one. Below are the approximate costs of what a mundane weapon should cost based on the 1st party mundane weapons.
- Simple melee weapons should usually cost between 1 sp and 5 gp
- Simple ranged weapons usually shouldn't cost more than 25 gp
- Martial melee weapons should usually cost between 5 and 50 gp
- Martial ranged weapons should usually cost between 25 and 100 gp
- Renaissance weapons costs vary greatly, but they should usually fall between 50 and 500 gp
- Modern and futuristic items are assumed to be anachronistic in a vanilla D&D campaign, so do not have a purchase cost(—).  Specific campaigns in which these items are considered "mundane" may list prices.
Considerations for the cost include:
- The materials used. For example, a steel-hafted polearm will cost more than a wooden one. Even if the weapon statistics are the same, it matters when the DM needs to adjudicate (such as what might burn, or what is magnetic). It could conceivably matter for a homebrew class's weapon proficiencies, for example, if the class is restricted to cheaper wooden weapons.
- If the item has some versatility (not as in the versatile property!). For example, if the weapon can deal more than one type of damage, this could add an extra 5 gp to its value.
While weapons can have a variety of different properties, there are some combinations of properties that a singular weapon should not have.
- Heavy weapons may not have the light property
- Two-handed weapons may not have the light or versatile properties
- Light weapons may not have the versatile property
Even more so than mundane weapons, a homebrew piece of armor should be unique and not serve the same purpose as another piece of armor, whether homebrew or official. Below you can find a few pointers on how to create a piece of armor.
- Armor should fit into the general theme of medieval armor (no steampunk armor)
- Armor should generally fit into its appropriate category (no heavy metal light armor)
- Light armor should add your Dexterity modifier
- Medium armor should add your Dexterity modifier, but should have a maximum such as (max 2)
- Heavy armor should just provide a static Armor Class, such as 15
A piece of armor's cost should be reflective of how much AC the armor provides, what material the armor is made out of, whether it has any requirements, and whether it has any special properties. See 5e SRD:Armor for the costs of armor of mundane 1st party armor and 5e Armor for the costs of several homebrew pieces of armor.
If you have ever wanted to create a bobble and feel like it wouldn't fit well as a common magical item, well you’re in luck, D&D Wiki is host to an ever-growing list of trinkets on the 5e Trinkets page. While some PC's may consider these items to be worthless, they have the potential to both create interesting backstories on how you obtained such an item and they can be used for plot purposes by DM's. Remember, these items are meant to be mysterious and whimsical, so have fun using and creating them.
Tools are specialized equipment that allows you to do things you normally wouldn’t be able to do such as create glasswork, create a painting, or sew a blanket. A tool always has an associated tool proficiency, so you need to describe what the character can achieve with that proficiency, e.g. proficiency with this tool lets you add your proficiency bonus to any ability checks you make to (whatever the tool does). Any ability check you make with a tool that you are proficient in allows you to add your proficiency bonus to the check.
Tools should not state what ability score is required to use them as the use of a tool should not be tied to a single ability score,  and DM’s should interpret how a tool is used. For example, a DM could ask for an Intelligence check to come up with on how to incorporate a reloading feature with tinker’s tools onto a crossbow and a Dexterity check to see whether you could create such an apparatus. See 5e PHB pp. 154 for the list of descriptions on 1st party artisan tools.
While often hard to obtain without the right contacts, poisons they can be extremely useful to a trained assassin. The effects of poison and how they are applied vary considerably, but there are some things that should remain consistent across all poisons. Creatures should be able to apply poisons by contact, ingestion, inhalation, or through an injury, poisons should always require a saving throw, poisons should never just kill a creature, and the price of a poison indicates its cost per single dose. Info on what each how poisons are applied can be found on 5e DMG pp. 257.
Mounts and Vehicles
The speed of vehicles is measured in mph and the speed of mounts is measured in movement speed per turn. As a rule of thumb, 1mph equals a movement speed of 10 feet.
Mounts are common tamable creatures that can be used to carry gear and pull vehicles. Creating a mount is fairly straightforward, all you need a creature name, a gold cost, a movement speed, and a carrying capacity. When you are creating the mount think about how its size and physical characteristics translate into stats. See 5e PHB pp. 156-7 for more info on mounts.
See the 5e DMG pp. 119.
- General Balance
If you are unsure of how balanced a magical item you are creating would be, it is a good idea to look up a relevant 1st party magical item to compare it to. See the 5e DMG pp. 150-214 for the full list of magical items and see 5e SRD:Magic Items for magical items that appear in the System Reference Document(SRD). In terms of magical item balance, remember that items that give bonuses that you don't need to hold are better than those you do need to hold, as demonstrated by the +2 shield and the +1 armor being the same rarity(rare).
- Do’s and Don’ts
While you do have a lot of creative freedom when creating a magical item, there are some guidelines you should follow when creating a magical item.
- Don’t have a magical item gain additional effects or charges based on your level, ability scores, class, race, other equipment, or through other means. A piece of equipment should also not grant additional effects to a PC's already existing traits or features.
- Don't include a gold cost for a magical item as the purchasing of magic items and their cost should entirely be under the purview of the DM in the specific campaign that they are running.
- Do use the standardized durations: 1 round, 1 minute, 10 minutes, 1 hour, etc. over durations with round-counting, e.g. 6 turns, 1d4 + 1 turns
- Advantage on any check is extremely strong, if given consider making it circumstantial, for example, you have advantage on Charisma (Persuasion) checks made against dragons.
- Do allow an item to have a prerequisite to attune to it. Examples include 15 Strength, class/es, and a spellcaster. Try and avoid homebrew class requirements as well, as it is far too strict of a requirement.
- Don’t change how much damage a weapon itself deals (a longsword should deal 1d8/10 not 2d8/2d10) or how much Armor Class a piece of armor itself gives (plate should only give 18 AC).
- Don't have an effect that requires an on hit saving throw with every hit as it greatly slows down combat.
- Do explain exactly what bonuses a magical item grants. A +2 battleaxe does not inform players what the +2 entails. Does it mean a bonus to spell attack rolls, just damage rolls, or something else?
- Items themselves shouldn’t have a level requirement, but the DMG does state that PC's should typically obtain certain rarity magical items when they are around a certain level . See the Magic Item Rarity table for specifics.
Remember, a character can only attune to 3 magical items at any time, and PC’s who attempt to attune to any more must first end their attunement with one of their items before being able to attune to another. Also, if a magical item can be abused by passing it around or if having multiple items with bonuses would make a PC too strong, an item should require attunement.  Magical items themselves should never allow you to attune to more magical items, or else PC’s power can get out of control. Attunement slots should never be adjusted by player-accessible entities, as only the DM’s should have full control over this power. By giving a PC an item that allows for them to attune to more magical items, it prevents the DM from fine-tuning the power granted to PC’s by magical items.
- Charges and Regaining Powers
So you want to give a magical item the ability to cast spells multiple times or use power from a pool of power, then creating a magical item with charges should suit your need. Charges can be used to use homebrew properties items have or casting spells, in which case the charge cost should typically cost the same as the spell slot level. It is, however, important to remember that magical items have their own powers, and don’t draw power from you. As such, magical items should regain a certain amount of charges and their uses of certain properties at dawn or after a certain amount of days. This is based on the precedent set by WotC for magical items. See these for an example of how a magical item's properties are recharged figurine of wondrous power, wand of lightning bolts, and staff of thunder and lightning.
Potions and Other Consumable Magic Items
Creating consumable items can be a fun endeavor. These items effects can provide a variety of boons and buffs to a PC or they can be downright silly. Regardless of what the item does, it should only provide an effect when used or drunk and the effect the consumable item provides shouldn't be permanent. Doing so would be like making an item has to require attunement to be balanced not require attunement and is effectively just giving PC's bonus traits/abilities. Also remember, when you use a consumable item such as a potion, scroll, or something else, the item is used up. 
Generally, curses on items shouldn’t be too deliberating since severely punishing a player for attuning to a magical item doesn’t feel good as the PC and often times is just downright cruel. Cursed items should also require attunement as to not overtly punish PC's for being inflicted by a curse just for finding a magical item and because all 1st party cursed item require attunement. Also, when making a cursed item, the item itself should be balanced as a standalone item without the curse, as again, 1st party cursed items are balanced this way. Remember, that attunement to a cursed item cannot be undone except through use of a remove curse spell.  Having to suffer the effects of curse that you can not get rid of because it needs a spell of a much higher level than you have access to can be very frustrating for a player, especially if their character is dramatically changed (gender change, becoming another race, turning a neutral good hero into an chaotic evil murder without talking to your pc about it, etc.) and the effect has no relevance to the story. Remember that cursed items too are rated by rarity.  This helps you to balance the effects of the curse to something appropriate to the level at which the player character will be usually encountering the item. In general, no effect of a cursed item is permanent. In addition, no cursed item provides benefits unless it helps it fulfill the function of its curse, neither is it unique. (A bag of devouring function as a bag of holding so you want to reach inside it, a berserk axe grants an attack bonus so its berserk wielder can better kill people, etc.) Unique items with powerful, long lasting advantages and penalties are the purview of artifacts, the deck of many things (which functions more as an artifact and campaign killer than a "normal" magic item) or items that grant access to the wish spell. Remember, you are trying to develop something FOR your PC's to interact and tell a story with, not to humiliate or punish them. Lastly, your players are very likely to find a way to weaponize cursed items against their enemies or for personal gain, so be careful with items that self replicate, control creatures, polymorph something into another form, etc.
The 5e Dungeon Master's Guide contains an excellent guide on how to create sentient items, covering generating its ability scores, its method of communication, special senses, alignment, characteristics, purpose and conflict on page 214-6 which should be referenced throughout the process. Regardless, this design guide will go through the nuances of creating a sentient item as sentients items are one of the hardest types of equipment to create. But first, know that sentient items shouldn't just be more powerful than other items of its rarity, though they can have a variety of unique effects.
- General Info
The first things to consider when making a sentient item is the name of the item and the name of the sentience that is occupying this item. This name may be identical, but it isn't the name of the sentient item should reflect the appearance and properties of the said sentient item. After that, the item likely needs a unique appearance that sets it apart from any regular item. Finally, you may include a summary as to how this sentient item was created and its background.
Here you should describe the sentient item's personality traits, ideals, bonds, flaws, as if you were making a new character, including what the weapon likes, dislikes, its goals, how the item reacts to a wielder, how it could get into arguments with that wielder and as such create drama for the story.
Finally, a model example of how a sentient item should be formatted and balanced can be found in Sunlight Rose (5e Equipment).
- 5e DMG pp. 267
- 5e PHB pp. 154
- 5e DMG pp. 135
- 5e DMG pp. 138
- 5e DMG pp. 285
- 5e DMG pp. 139
- 5e DMG pp. 138-9
- 5e DMG pp. 135