Vellum GUI

Vellum is a small web engine inside Minecraft. Screens, inventories, HUD and map can be expressed as HTML page, and Vellum lays it out, animates it, runs its scripts and draws it with the normal GUI renderer.

You don't need to install this on its own. It's a library: mods that use it list it as a dependency, and launchers install it with them.

The inspiration for Vellum was two-fold: 

1. I'm a web developer and my Minecraft GUIs have always looked bad
2. LLMs are better at web development than Minecraft GUI development
   
   

Vellum helps in both these cases.

What you get

• Most of CSS: block, inline, flexbox, grid and positioning, plus transitions and @keyframes. It's a 90-10 solution, not a browser.
• The game's own look by default. Buttons, text fields, panels, slots and tooltips use vanilla sprites and the game font, so an unstyled page already fits in.
• Real inventories. Put <slot index="0"> wherever you want a slot and vanilla mechanics will Just Work(tm)
• Minecraft specific elements: <item>, <slot>, 3D <entity> and <model>, sprites, translations and player heads.
• JavaScript with Vue-style templates (v-for, v-if, v-model, @click). 
• HUD overlays, narration/accessibility support, and a standalone previewer with hot reload, so you (or your agent) can build a page without launching the game.

For mod developers

<div class="mc-panel chest">
  <div class="mc-label">{{ title }}</div>
  <div class="grid"><slot v-for="i in 27" :index="i - 1"></slot></div>
</div>
<style>
  .grid { display: grid; grid-template-columns: repeat(9, 18px); }
</style>

VellumScreens.registerContainer(MyMenus.CHEST, "mymod:vellum/chest.html");
VellumScreens.open("mymod:vellum/journal.html", data).driver()
        .onMessage("save", value -> Journal.save(value.getAsJsonObject()));

Depend on it from maven.maxleiter.com (dev.vellum:vellum-neoforge-26.3:0.4.1, and the same for Fabric and 1.21.1), and make it a required dependency of your mod rather than bundling it.

Docs: API, scripting, porting an existing screen.

Servers

A server mod can open a page on a player's client, push data to it and get messages back. Since a server might be hostile, scripts run in a sandbox with no Java access, no network access, no file access, and sensible resource caps. Players can always close a page with Shift+Esc, and config/vellum.properties lets them block server pages entirely.

LLMs were used in the development of Vellum.

Vellum is MIT licensed. It bundles Mozilla Rhino (MPL-2.0) with a few patches, which are in the repo under rhino/patches/.