Cosmetics with Blockbench — LeiCraftClient Docs

LeiCraftClient cosmetics are OptiFine player-item models: simple 3D boxes attached to a body part, plus a PNG texture. You make them in Blockbench, a free 3D editor for Minecraft models, with the OptiFine Player Models plugin.

What you need

Blockbench, as the desktop app or the web app at blockbench.net. At the time of writing the current version is 5.2.
The plugin OptiFine Player Models by Ewan Howell (installed from inside Blockbench, see below).
A LeiCraftClient community page to upload to. See Upload and publish.

Set up Blockbench

Install the plugin

In Blockbench, open File → Plugins…, switch to the Available tab and search for OptiFine Player Models. Click Install.

Create a project

Open File → New (or use the start screen) and choose OptiFine Player Model. Click Create New OptiFine Player Model.

Look at the groups

The new project already contains six groups: head, body, leftArm, rightArm, leftLeg and rightLeg. You can't delete them, and every cube must be inside one of them. The group decides which body part your item is attached to.

Build the model

Add cubes inside the group of the body part your item should follow. You can create your own groups inside these six groups to keep things organized.

Group	Follows	Ideas
`head`	Head turning and nodding	Hats, horns, halos, glasses
`body`	Body, also when sneaking	Backpacks, wings, scarves
`leftArm`, `rightArm`	Arm swinging	Bracelets, shoulder pads, gloves
`leftLeg`, `rightLeg`	Leg movement while walking	Boots, leg bands

An item can use several groups at once, for example a pair of boots on both legs.

What is not possible

No animations. OptiFine player models are static boxes. Your item still moves with its body part, because it follows the vanilla movement (walking, arm swings, sneaking, head turning). It can't have its own animation.
Only these six body parts. You can't attach anything to the cape, the elytra or an item in the hand.
Arms on slim skins: slim (Alex) arms are 1 pixel narrower than wide (Steve) arms, so arm items made for one arm type don't sit perfectly on the other. Make a second variant for this, see Skin-model variants.

Tips for clean models

A cube's faces are only drawn from the outside. Flat cubes with a thickness of 0 are visible from both sides, so they work well for thin parts like feathers or flat signs.
In-game, every texture pixel is either fully visible or fully transparent. Half-transparent pixels don't make glass-like see-through parts.
Keep the Blockbench project file (.bbmodel) so you can edit the model later. You only upload the exported .cfg file.

Paint the texture

The new project uses a 64×64 texture by default. Paint it in Blockbench's Paint tab or in any image editor.

Save the texture as a PNG file. In Blockbench, use the texture's right-click menu to save or export it as an image.
The PNG should have the same size as the texture in your project. A texture with exactly double or four times the size (for example 128×128 for a 64×64 project) also works and gives more detail, because the UVs are scaled to the image.
The upload accepts textures up to 1024×1024 pixels and 2 MB.

Use the player's skin

The plugin has a project option Use Player Texture (probably under File → Project…, depending on your plugin version). With it, the mod draws the model with the wearer's own skin instead of your texture.

At the time of writing, the 3D preview on the website does not support this option and always shows the texture you uploaded. The Creator Studio still requires a texture for every variant, so upload one anyway, for example a sample skin. Check the real look in-game.

Export the model

Open File → Export → Export OptiFine Player Model. Blockbench saves a .cfg file (a JSON text file). Save the texture PNG separately: the upload always needs both files.

The plugin has a second export, Create OptiFine Player Model Config, which asks for a Minecraft username. That one is for testing with OptiFine on your own computer. You don't need it for LeiCraftClient.

What the exported file looks like

You don't need to edit the file by hand. This shortened example of a Christmas hat shows the structure:

{
  "type": "PlayerItem",
  "credit": "Made with Blockbench",
  "textureSize": [64, 64],
  "models": [
    {
      "type": "ModelBox",
      "attachTo": "head",
      "invertAxis": "xy",
      "translate": [0, 0, 0],
      "submodels": [
        {
          "id": "christmas_hat",
          "invertAxis": "xy",
          "translate": [0, 0, 0],
          "boxes": [
            { "coordinates": [-5, 8, -5, 10, 1, 10], "textureOffset": [0, 0] },
            { "coordinates": [-4, 9, -4, 8, 1, 8], "textureOffset": [0, 11] },
            { "coordinates": [-3, 10, -3, 6, 1, 6], "textureOffset": [0, 20] }
          ]
        }
      ]
    }
  ]
}

textureSize is the size of your texture in the project.
Each entry in models is one body-part group. attachTo names the body part.
boxes are your cubes: coordinates is position and size ([x, y, z, width, height, depth]), and textureOffset (or one UV per face) says where the cube's texture is.
submodels are the groups you created inside a body-part group.

Upload limits

What	Limit
Model file	JSON (`.cfg` or `.json`), at most 256 KB
Body-part groups (`models`)	1 to 64
Parts (groups and sub-groups)	at most 512
Cubes	at most 2048
Nesting depth of groups	at most 16 levels
Texture	PNG, at most 1024×1024 and 2 MB

When you upload, the model is checked and saved again with only the parts LeiCraftClient understands. A texture path inside the model, sprites and any unknown keys are removed. The Creator Studio tells you about each removal in a Note message. This is why you always upload the texture as its own file.

Common upload problems

Next: make variants for wide and slim arms if your item touches the arms, then upload and publish it.