Regarding the "Magic Item Power by Rarity" table (DMG, p. 285) that was referred to in another response, I have found that magic items add rarity to increase their frequency of use or range of effects. So, a good set of rules of thumb are:

1. Once per day is the base rarity
2. A charged item regains d3-d6 +1 charges per day at a cost of one rarity higher than the spell that created it
3. An 'at-will', or continuous effect, item produces a magic item that is two rarity levels higher than its originating spell
4. If the spell requires Concentration, then the magic item typically requires attunement
5. If it has multiple effects then increase the rarity by at least one more level, unless it has a self-destruct mechanism, like several Staffs with multiple spells.

For example:

• A charged wand of Magic Missile (L1) is Uncommon
• A charged wand of Polymorph (L4) is Very Rare and requires attunement
• An 'at-will' Ring of Featherfall (L1) is Rare and requires attunement
• A charged Staff of Frost has multiple spells, with Wall of Ice (L6) as it's highest level spell, but can be destroyed by overuse, so it's Very Rare.

Finally, if the result is overpowered then the rarity is probably one higher, e.g. Ring of Invisibility (L2) is Legendary, not Very Rare. And if it only gives a bonus to a single ability check, or other limited effect, then it's probably one rarity lower, as with the 'at-will' Ring of Jumping (L1), which is only Uncommon, not Rare as we might otherwise expect.

Obviously, this method isn't perfect or complete, but I do find it to be a useful heuristic for building custom magic items. Hopefully that helps!

Regarding the "Magic Item Power by Rarity" table (DMG, p. 285) referenced in illustro's answer, I have found that magic items add rarity to increase their frequency of use or range of effects. So, a good set of rules of thumb are:

1. Once per day is the base rarity
2. A charged item regains d3-d6 +1 charges per day at a cost of one rarity higher than the spell that created it
3. An 'at-will', or continuous effect, item produces a magic item that is two rarity levels higher than its originating spell
4. If the spell requires Concentration, then the magic item typically requires attunement
5. If it has multiple effects then increase the rarity by at least one more level, unless it has a self-destruct mechanism, like several Staffs with multiple spells.

For example:

• A charged wand of Magic Missile (L1) is Uncommon
• A charged wand of Polymorph (L4) is Very Rare and requires attunement
• An 'at-will' Ring of Featherfall (L1) is Rare and requires attunement
• A charged Staff of Frost has multiple spells, with Wall of Ice (L6) as it's highest level spell, but can be destroyed by overuse, so it's Very Rare.

Finally, if the result is overpowered then the rarity is probably one higher, e.g. Ring of Invisibility (L2) is Legendary, not Very Rare. And if it only gives a bonus to a single ability check, or other limited effect, then it's probably one rarity lower, as with the 'at-will' Ring of Jumping (L1), which is only Uncommon, not Rare as we might otherwise expect.

Obviously, this method isn't perfect or complete, but I do find it to be a useful heuristic for building custom magic items. Hopefully that helps!

Regarding the "Magic Item Power by Rarity" table (DMG, p. 285) that was referred to in another response, I have found that magic items add rarity to increase their frequency of use or range of effects. So, a good set of rules of thumb are: 1) once per day is the base rarity; 2) a charged item regains d3-d6 +1 charges per day at a cost of one rarity higher than the spell that created it; & 3) an 'at-will', or continuous effect, item produces a magic item that is two rarity levels higher than its originating spell; 4) if the spell requires Concentration, then the magic item typically requires attunement; and 5) if it has multiple effects then increase the rarity by at least one more level, unless it has a self-destruct mechanism, like several Staffs with multiple spells.

For example, a charged wand of Magic Missile (L1) is Uncommon; a charged wand of Polymorph (L4) is Very Rare and requires attunement; an 'at-will' Ring of Featherfall (L1) is Rare and requires attunement; a charged Staff of Frost has multiple spells, with Wall of Ice (L6) as it's highest level spell, but can be destroyed by overuse, so it's Very Rare.

Finally, if the result is overpowered then the rarity is probably one higher, e.g. Ring of Invisibility (L2) is Legendary, not Very Rare. And if it only gives a bonus to a single ability check, or other limited effect, then it's probably one rarity lower, as with the 'at-will' Ring of Jumping (L1), which is only Uncommon, not Rare as we might otherwise expect.

Obviously, this method isn't perfect or complete, but I do find it to be a useful heuristic for building custom magic items. Hopefully that helps!

Regarding the "Magic Item Power by Rarity" table (DMG, p. 285) that was referred to in another response, I have found that magic items add rarity to increase their frequency of use or range of effects. So, a good set of rules of thumb are:

1. Once per day is the base rarity
2. A charged item regains d3-d6 +1 charges per day at a cost of one rarity higher than the spell that created it
3. An 'at-will', or continuous effect, item produces a magic item that is two rarity levels higher than its originating spell
4. If the spell requires Concentration, then the magic item typically requires attunement
5. If it has multiple effects then increase the rarity by at least one more level, unless it has a self-destruct mechanism, like several Staffs with multiple spells.

For example:

• A charged wand of Magic Missile (L1) is Uncommon
• A charged wand of Polymorph (L4) is Very Rare and requires attunement
• An 'at-will' Ring of Featherfall (L1) is Rare and requires attunement
• A charged Staff of Frost has multiple spells, with Wall of Ice (L6) as it's highest level spell, but can be destroyed by overuse, so it's Very Rare.

Finally, if the result is overpowered then the rarity is probably one higher, e.g. Ring of Invisibility (L2) is Legendary, not Very Rare. And if it only gives a bonus to a single ability check, or other limited effect, then it's probably one rarity lower, as with the 'at-will' Ring of Jumping (L1), which is only Uncommon, not Rare as we might otherwise expect.

Obviously, this method isn't perfect or complete, but I do find it to be a useful heuristic for building custom magic items. Hopefully that helps!