file.json

{ "frames": {
   "file 0.ase": {
    "frame": { "x": 0, "y": 0, "w": 32, "h": 32 },
    "rotated": false,
    "trimmed": false,
    "spriteSourceSize": { "x": 0, "y": 0, "w": 32, "h": 32 },
    "sourceSize": { "w": 32, "h": 32 },
    "duration": 100
   },
   "file 1.ase": {
    "frame": { "x": 32, "y": 0, "w": 32, "h": 32 },
    "rotated": false,
    "trimmed": false,
    "spriteSourceSize": { "x": 0, "y": 0, "w": 32, "h": 32 },
    "sourceSize": { "w": 32, "h": 32 },
    "duration": 100
   },
   "file 2.ase": {
    "frame": { "x": 64, "y": 0, "w": 32, "h": 32 },
    "rotated": false,
    "trimmed": false,
    "spriteSourceSize": { "x": 0, "y": 0, "w": 32, "h": 32 },
    "sourceSize": { "w": 32, "h": 32 },
    "duration": 100
   }
 },
 "meta": {
  "app": "http://www.aseprite.org/",
  "version": "1.1.0.1",
  "image": "file.png",
  "format": "RGBA8888",
  "size": { "w": 96, "h": 32 },
  "scale": "1"
 }
}

Hmm.. will frame.w ever differ in value from spriteSourceSize.w or sourceSize.w? (and same for the heights)

Are these documented somewhere? 🤔
Apologies if the difference is obvious!

I have the same question unfortunately.

The answer is yes when using --trim for a sprite sheet.

"frame" seems to be the rectangle in the output sheet including padding, whereas "spriteSourceSize" excludes it.