jsonui-render-mcp

An MCP server that draws Minecraft Bedrock JSON UI screens, so a resource pack's layout can be looked at without a device.

It reads the pack you produced and Mojang's real UI files, expands @ inheritance and $variables, and reports anything it does not implement instead of guessing.

Setup

pip install mcp pillow

Then call the setup_samples tool once. It sparse-clones Mojang/bedrock-samples for the vanilla UI definitions and textures. Nothing from Mojang is bundled here.

Environment:

Register it:

{
  "mcpServers": {
    "jsonui-render": {
      "command": "python3",
      "args": ["/path/to/jsonui-render-mcp/server.py"]
    }
  }
}

Related MCP server: Datapack MCP Server

Tools

The pack dump

render_screen reads a directory your build writes:

controls.json          name -> control
screens.json           [{name, width, height, body, title, background, marker}]
textures/*.png         your own textures, flat
textures/nineslice.json   name -> border, as an int or [l, t, r, b]

Two things worth knowing

• layer orders a sibling group and nothing wider. A screen-wide depth and an accumulating one both look plausible and both contradict a device. What a sibling is ordered by is its subtree's deepest layer, not the number on its own root: a plate whose recess carries 20 sits behind a figure whose panel carries nothing, and by their own numbers the recess would paint over it.

• The anchor rule is: the child's anchor_to point lands on the parent's anchor_from point, then the offset applies. check_anchors holds the renderer to it.

What it does not do yet

• clips_children is honoured, but only where the window measures: fill and common.scrolling_panel's own internals are not modelled, so a scroll view port comes out nought by nought. Those are reported and drawn unclipped — the content appears at full height, over whatever is beneath it.

• Bindings other than a form's caption and texture.

• %cm is read as the content size, not the largest child.

• Item pictures come from vanilla paths only.

A device is still ground truth. When the two disagree, this is wrong.