Rarity and weights

Rarity in nfty is not a label you assign. It comes out of four settings, and a finished Set reports it as a share of the collection. This page explains how the settings combine; for the steps, see Weights and rarity.

The four inputs

Setting	Lives on	Decides
Recipe weight	CookBook	How often each character type is rolled. 0 shelves a Recipe.
Variant weight	Ingredient	How often each option of a layer is picked, relative to its siblings. 0 shelves a variant.
Absent chance	Recipe, per layer	The percent of assets that leave the layer out entirely. 0 always present, 100 never.
Color range weight	Ingredient (Dynamic)	How often each hue and saturation range is used when a color is rolled.

Weights are relative. A variant at weight 3 is picked three times as often as one at weight 1; weights never need to add up to anything.

An asset is rolled in this order: Recipe by weight, then for each layer in paint order: absent or present, then a variant by weight, then (for a Dynamic layer) a range by weight and a color inside it.

Why the absent chance is on the Recipe

One Ingredient file can sit in several Recipes, and in a Kitchen it can be shared between projects. The same hat may be guaranteed on one character and a chase item on another, so the chance belongs to the Recipe that stacks it.

Leaving a layer out is better than adding an empty variant. An empty variant on a Dynamic layer still rolls a color, so two assets that both show nothing get different DNA and the unique DNA figure inflates for no visible reason. An absent layer rolls no color and adds nothing to the DNA.

Rules change the odds too

A rule rejects some combinations, and nfty re-rolls the whole asset (Recipe included) when one fires. So rules move probability around: if stone bodies may never carry keypads, the remaining locks become slightly commoner on stone chests. nfty's exact odds account for this; a simple product of shares does not.

Predicted versus observed

Where	Reports	From
Ingredient panel's IN RECIPE / OVERALL columns, nfty stats	What the weights predict	The CookBook
set.json, the Set browser's RARITY table, nfty inspect <set>	What a cook actually produced	The Set

OVERALL is the share of the whole collection that gets a variant, after the Recipe's weight and the layer's absent chance; aim at that, because it is what a buyer sees. A Set's observed shares drift from the prediction by chance, less so the larger the Set.

Rarity is collection-wide: "3% of assets have this hat" changes the moment the collection grows. Extending a Set rewrites every existing item's rarity field. Images and DNA never change.

An asset's combined chance

The Set browser shows, beside each asset, its combined chance (for example this combo 1 in 43,200). When nfty can find the CookBook that cooked the Set (by its hash), the figure is exact: the probability of that whole roll, with rules accounted for. When it cannot, the figure is marked ~ and is the product of the trait shares, which assumes the layers are independent; its tooltip says so. You can read rarities as percentages or as odds (1 in 24); the page header toggles every figure at once.

Colors and absences are traits

From metadata shape 2 (every new cook), each Dynamic and Static layer publishes a "<Layer> Color" trait named from the rolled color, and a left-out optional layer publishes None. Both count in the rarity table like any other trait. See Color traits and None.