SkelToJson - Spine 2D Binary to JSON Converter

Convert Spine 2D binary .skel files to human-readable JSON — supports Spine 4.2.x and 4.3.x.

What is Spine 2D?

Spine is a 2D animation tool widely used in games, apps, and web content. It lets artists rig a skeleton of bones onto 2D images, then animate them with keyframes — producing smooth, lightweight character animations without frame-by-frame sprite sheets.

.skel vs .json — What's Inside?

Spine exports skeleton data in two formats:

.skel — Binary format (compact, not readable)

The .skel file is a binary encoding of the entire skeleton. It's optimized for size and loading speed, but completely unreadable — it's just raw bytes:

c2b3a848 2ee43256 07342e32 2e343300
c3160000 c3de0000 43960000 44610000
42c80000 00011f61 6e746963 69706174
696f6e ...

.json — JSON format (human-readable, editable)

The JSON export contains the same data in a structured, readable format. Here's the structure:

Conversion Example

Input: anticipation.skel — 224 bytes of binary data

Output: anticipation.json — structured, readable:

{
  "skeleton": {
    "hash": "2ee43256c2b3a848",
    "spine": "4.2.43",
    "x": -150,
    "y": -444,
    "width": 300,
    "height": 900,
    "referenceScale": 100
  },
  "bones": [
    { "name": "root" }
  ],
  "slots": [
    {
      "name": "anticipation",
      "bone": "root",
      "attachment": "anticipationv2/anticipationv2_"
    }
  ],
  "skins": [
    {
      "name": "default",
      "attachments": {
        "anticipation": {
          "anticipationv2/anticipationv2_": {
            "y": 6,
            "width": 300,
            "height": 900,
            "sequence": { "count": 31, "start": 0, "digits": 2, "setup": 0 }
          }
        }
      }
    }
  ],
  "animations": {
    "animation": {
      "attachments": {
        "default": {
          "anticipation": {
            "anticipationv2/anticipationv2_": {
              "sequence": [
                { "mode": "loop", "index": 0, "delay": 0.03333 },
                { "time": 1, "mode": "loop", "index": 0, "delay": 0.03333 }
              ]
            }
          }
        }
      }
    }
  }
}

This is a simple skeleton with 1 bone, 1 slot, and a sequence-based attachment animation. Real game skeletons will have hundreds of bones, complex mesh deformations, IK chains, physics simulations, and dozens of animations.

Installation

pip install SkelToJson

CLI Usage

# Convert a single file
skel-to-json skeleton.skel

# Convert with custom output path
skel-to-json skeleton.skel -o output.json

# Convert all .skel files in a directory
skel-to-json skeletons/

# Convert directory with custom output directory
skel-to-json skeletons/ -o output/

Python API

from SkelToJson import convert_skel_to_json, convert_directory, SkelConverter

# Convert a single file
convert_skel_to_json("skeleton.skel", "skeleton.json")

# Convert all .skel files in a directory
convert_directory("skeletons/", "output/")

# Low-level: convert raw bytes to dict
converter = SkelConverter()
result = converter.convert(skel_bytes)

Supported Formats

License

MIT