Rarity chance pools¶

Use rarity_chances.json to give an item a custom weighted roll.

Basic format¶

{
  "minecraft:diamond_sword": {
    "COMMON": 20,
    "UNCOMMON": 25,
    "RARE": 25,
    "EPIC": 20,
    "LEGENDARY": 8,
    "MYTHICAL": 2
  },
  "examplemod:boss_blade": {
    "EPIC": 50,
    "LEGENDARY": 35,
    "MYTHICAL": 14,
    "SUPREME": 1
  }
}

Use the full registry ID: modid:item_name.

Weight rules¶

Weights are relative integers.
Only positive weights enter the pool.
A missing tier cannot roll.
The numbers do not need to total 100.
A zero-only or empty pool falls back to Common.

Chance formula:

tier weight ÷ sum of all positive weights

Use the odds calculator to check a custom pool.

Change vanilla odds¶

Vanilla equipment already appears in rarity_chances.json. Edit those entries directly.

Do not change TOML defaultPool and expect diamond or netherite gear to follow it. The automatic pool is only for recognized equipment without an explicit JSON entry, usually modded gear.

Make a deterministic tier¶

A one-tier pool still stores a normal roll but always chooses the same tier:

{
  "examplemod:quest_pickaxe": {
    "SUPREME": 1
  }
}

This is the recommended way to make deterministic utility gear because its stored rarity will also control perk count and perk-tier quality.

Fixed rule versus one-tier pool¶

Goal	Use
Cosmetic tier for a collectible	`custom_rarities.json`
Random equipment roll	`rarity_chances.json`
Guaranteed equipment tier with normal stored rarity	One-tier chance pool
Guaranteed utility-tool tier and matching perk quality	One-tier chance pool

Avoid defining a fixed rarity and a random pool for the same utility tool. The visible fixed tier can outrank the hidden stored roll while utility perks still use the stored roll, producing mismatched quality.

When an item rolls¶

An explicit pool item rolls when it is first revealed—normally when placed in a player's main hand. Login and respawn are catch-up triggers.

Pool changes affect only unrolled items. The stored result on existing stacks remains.

Modded equipment with no explicit entry¶

The mod attempts to recognize combat weapons, armor, shields, and utility tools. Recognized items use defaultPool automatically.

If detection misses an item, add it explicitly to this JSON. If it rolls rarity but has no useful stats, add a complete package to rarity_attributes.json as well.

SetID-specific pools¶

Use setid_raritychances.json when only a tagged variant of an item should use the pool. See SetID item variants.

Apply changes¶

Run:

/sr reload

The new pool is used by future unrolled items. It does not reroll existing stacks.