A MotionDoc is a Lottie-like — but own — animation document. It is produced by the Figma plugin (Figma Motion → MotionDoc) and consumed by @blinn-motion/core. The format is intentionally small, time-based (seconds), renderer-agnostic, and human-readable enough to hand-author for tests.
Design goal: anything the engine can play, the Figma converter can emit — and the format stays readable. See the full schema for every field.

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Top level

{
  "format": "motion-engine",
  "version": "1.0",
  "meta":   { "name": "Card intro", "source": "figma" },
  "duration": 1.2,                                  // timeline length, SECONDS
  "fps": 60,                                         // suggested sampling fps
  "stage":  { "width": 375, "height": 600, "background": "#0E1116FF" },
  "layers": [ /* Layer[], painted back-to-front */ ]
}

​
Layers nest

A layer’s base position is relative to its parent’s box (top-level layers are relative to the stage). Children inherit the parent’s animated transform — exactly like the DOM. That nesting is why a card can move and its badge moves with it. 
{
  "id": "card",
  "name": "Card",
  "type": "rect",                       // rect | ellipse | text | image | vector | group
  "base": {
    "x": 44, "y": 200, "width": 287, "height": 200,
    "opacity": 1, "rotation": 0, "scaleX": 1, "scaleY": 1,
    "anchor": { "x": 0.5, "y": 0.5 },   // transform-origin, 0..1 of the box
    "cornerRadius": [24, 24, 24, 24],   // [tl, tr, br, bl]
    "fill": { "type": "linear", "angle": 135, "stops": [
      { "pos": 0, "color": "#3B82F6FF" },
      { "pos": 1, "color": "#8B5CF6FF" }
    ] }
  },
  "tracks": [ /* Track[] */ ],
  "children": [ /* nested Layer[] */ ]
}

​
Tracks animate one property

Each track drives a single normalized property over the base value. The op decides how the sampled value combines with the base:
opresultmeaning
setvabsolute
offsetbase + vadditive
scalebase * vmultiplier
{
  "property": "translateY",   // see the property table in the schema reference
  "op": "offset",
  "unit": "px",
  "base": 0,
  "keys": [
    { "t": 0.0, "v": 80, "easing": { "type": "spring", "bounce": 0.45 } },
    { "t": 0.8, "v": 0,  "easing": { "type": "hold" } }
  ]
}
Multiple tracks can target the same property — they compose in order over the base. That’s how a spring entrance and a hover offset can stack cleanly.

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Keyframes hold a value at a time

{ "t": 0.0, "v": 120, "easing": { "type": "cubicBezier", "p": [0.42, 0, 0.58, 1] } }
  • t is absolute time on the timeline, in seconds.
  • v is a number, a [x, y] vector, a "#RRGGBBAA" color, a boolean, or a string.
  • easing governs interpolation from this keyframe to the next (out-interpolation, like CSS transition-timing-function). The last keyframe’s easing is ignored.
Before the first keyframe the value is held; after the last keyframe it is held. So a track only needs keyframes where something actually changes.

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A complete tiny example

This is a real, playable MotionDoc — a card that springs up and fades in while a badge spins.
card.motion.json
{
  "format": "motion-engine",
  "version": "1.0",
  "duration": 1.6,
  "fps": 60,
  "stage": { "width": 375, "height": 600, "background": "#0E1116FF" },
  "layers": [
    {
      "id": "card", "name": "Card", "type": "rect",
      "base": {
        "x": 44, "y": 200, "width": 287, "height": 200,
        "anchor": { "x": 0.5, "y": 0.5 }, "cornerRadius": [24, 24, 24, 24],
        "fill": { "type": "solid", "color": "#2F6BFFFF" }
      },
      "tracks": [
        { "property": "opacity", "op": "set", "unit": "none", "base": 1, "keys": [
          { "t": 0.0, "v": 0, "easing": { "type": "cubicBezier", "p": [0, 0, 0.58, 1] } },
          { "t": 0.45, "v": 1, "easing": { "type": "hold" } }
        ] },
        { "property": "translateY", "op": "offset", "unit": "px", "base": 0, "keys": [
          { "t": 0.0, "v": 80, "easing": { "type": "spring", "bounce": 0.45 } },
          { "t": 0.8, "v": 0, "easing": { "type": "hold" } }
        ] }
      ],
      "children": [
        {
          "id": "badge", "name": "Badge", "type": "ellipse",
          "base": {
            "x": 24, "y": 24, "width": 56, "height": 56,
            "anchor": { "x": 0.5, "y": 0.5 },
            "fill": { "type": "solid", "color": "#FFBE16FF" }
          },
          "tracks": [
            { "property": "rotation", "op": "offset", "unit": "deg", "base": 0, "keys": [
              { "t": 0.0, "v": 0, "easing": { "type": "linear" } },
              { "t": 1.6, "v": 360, "easing": { "type": "hold" } }
            ] }
          ]
        }
      ]
    }
  ]
}