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:

Variable	Default	What
BEDROCK_SAMPLES	~/.cache/bedrock-samples	the clone above
MINECRAFT_FONT	~/.aseprite-mcp/fonts/minecraft	a folder with font.json, ascii.png

Register it:

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

Tools

Tool	What
setup_samples	clone Mojang's UI files
list_screens	the screens a pack dump defines
render_screen	draw one, with the form's captions and icons
render_control	draw any control by name, including Mojang's own
check_anchors	hold the anchor rule to Mojang's dialogs

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.
• 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

• 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.