Asset fields

Field	Type/default	Meaning
prompt	string, required unless mirror, portrait, outfit, or a template loop (animation.template)	The subject wording wrapped by the selected style's prompt prefix and suffix. A template loop is described by its template; a v3, pro, or sentence (skeleton-v3 with no template) loop still needs the motion in words.
width / height	integer 16–8192	Per-asset dimensions for generators that accept rectangular output. Provider limits may be lower.
size	integer 16–8192	Per-asset square size where the generator uses one dimension.
file	string	Output path below the style's outDir; defaults to <category>/<assetId>.png.
category	string	Optional output subdirectory and logical grouping.
source	string	Manifest-relative committed art used instead of generation. For a set of PNG outputs (a frames animation, a tiles set) a path that is not a file is the stem of a hand edit laid beside the generated members (<stem>-<role>.png each); the set still generates. Mutually exclusive with revision.
sourceByStyle	object	Per-style source, keyed by style id; wins over source for that style. Written by pixelkiln edit for a hand edit of an asset that is in several styles.
remoteId	string	The provider's own id for art that already exists on the account, so adopt maps it without matching bytes: an object id, a character id, or <character id>#<animation group id>. Not part of the spec's identity.
revision	object	Controlled dependency on another asset: image-to-image, inpaint, or outpaint; on PixelLab also reduce-colors, correct-pixelart, remove-background, normal-map, the animate modes (animate, animate-pixminimax, animate-skeleton), interpolate, and edit-animation. engine: "pro-flash" selects PixelLab's Pro Flash tier for image-to-image/inpaint. See controlled revisions.
state	object	character styles: a pose or outfit of another character asset. See Characters.
animation	object	character styles: a loop of another character asset in one direction. directions (a list, instead of direction) declares the loop for several directions at once and fills the unnamed flips with mirrors; see One loop, several directions. mode: "skeleton-v3" with no template animates the asset's prompt as a sentence (3–15 frames, default 8; a v3 base); see Loops from a sentence. motionFrom (an asset id) makes a sentence loop follow another direction's loop and share its motion; directions writes it for you.
portrait	object	character styles: a bust of a base or state's south sprite, { "of": "<asset>", "size": 64 }; size is 16, 32, 48, 64 (default), 128, or 160. See Portraits.
outfit	object	character styles: an existing loop's frames re-clothed from an outfit image, { "of": "<loop asset>", "reference": "<image>" }, with optional additionalInstructions. See Outfit transfer.
mirror	string	Another asset of the same style flipped left to right, made locally at no cost. See Mirrors.
vfx	object	vfx styles, PixelLab only: the effect to render. { "preset": "explosion", "parts": [{ "name": "scorch_mark" }], "sprite": "art/chars/hero.png", "fps": 12 }; start from one preset or one recipe (a recipe JSON or a .vfx.json record), with optional parts, sprite, fps, and name. Or give a description (with optional artist: lite or pro, a local PNG sprite, and name) for PixelLab's paid VFX artist instead; it excludes preset, recipe, parts, and fps. Replaces prompt as the required field. See vfx and Described effects.
scene	object	map styles, PixelLab only: draw this object into a scene image, in its style. { "image": "scene.png", "placement": { "oval": 0.3 } }; placement is oval or rectangle (a fraction, 0.05–0.95) or mask (a PNG the size of the scene). See Drawing into a scene.
connect	object	terrain styles, PixelLab only: share a terrain with another set in the same style, keyed by this set's own side. { "lower": { "of": "coast", "terrain": "upper" } } makes this set's lower terrain coast's upper. The other set generates first; regenerating it makes this one stale. A sidescroller set connects only lower. Cycles are rejected.
batch	object	1dir styles: rides along on another 1dir asset's item_descriptions submission instead of generating on its own — { "of": "<leader asset id>", "index": <1-based slot> }. See 1dir.
pieces	array	uiAsset styles: exact shape regions (rounded_rect/circle/polygon) the panel is composited from, each with a unique id. See uiAsset.
elements	string array	uiAsset styles: named, auto-positioned UI scaffolds (button, health_bar, window, ...). Combine with pieces; omit both for a plain full-canvas panel. See uiAsset.
proportions	preset or object	character styles: this base's proportions, over the style's.
reference	string or object	character styles, bases: the character's own south-facing sprite (or { "south": ..., "east": ... }), which PixelLab rotates instead of drawing from the prompt. See Characters.
concept	string	character styles, pro bases: a manifest-relative concept image (up to 1024px) the design is seeded from.
styleCharacter	string	character styles, pro bases: this base's style anchor, over the style's.
providerInputs	JSON scalar/sequence map, {}	Named per-asset inputs consumed by the active provider. ComfyUI accepts scalars and, for frames, one ordered 2–64 value sequence. Image bindings upload PNG/JPEG inputs.
styles	string array, []	Restrict the asset to named styles. Empty means every style of the asset's kind: vfx styles for an asset with a vfx block, every other style otherwise.
promptByStyle	string map, {}	Replace only the asset prompt for a named style.
cell	[column,row]	The grid cell this asset owns in a mounted sheet; see stable-cell mounting.
outputRole	string	Select one structural output when a generator returns a set.
tags	string array, []	Asset tags added to provider objects where supported.

providerInputs is provider-owned and participates in generation identity. Changing a value makes only that asset stale. A provider may replace a local runtime path with a content hash before hashing the spec; unsupported providers reject non-empty inputs rather than ignoring them. Only a provider that declares a sequence contract may accept an array. ComfyUI uses the array named by providerOptions.comfyui.frames.vary; other inputs stay constant across the set.

One asset using the fields most projects reach for:

{
  "assets": {
    "anvil": {
      "prompt": "a compact blacksmith anvil",
      "promptByStyle": { "mono": "a compact blacksmith anvil, dark iron" },
      "width": 48,
      "height": 32,
      "category": "tools",             // assets/generated/base/tools/anvil.png
      "tags": ["prop", "forge"],
      "styles": ["base", "mono"],      // skip every other style
      "cell": [2, 0],                  // its cell on a mounted sheet
      "source": "edits/anvil.png"      // a hand edit stands in for the generated file
    }
  }
}