guikit — in-game GUI editor

Menus are built in the world, not by writing .mcfunction files. A chest minecart is the screen. Left-click is the click. Definitions live in storage guikit:lib (saved with the world) and survive /reload.

Target: Minecraft Java 26.3 (min_format / max_format 121).

The cart / click / redraw engine underneath is the old guikit runtime. Authoring moved off the #guikit:fill / #guikit:probe framework and into an editor.

Install

Drop this pack in the world's datapacks folder and /reload. On first load it seeds a published Welcome menu so there is something to open.

Play

Anyone (no operator permission):

/trigger guikit.open

That opens the list of published menus. A one-time chat line suggests the same command. Joining players are told once.

Edit (operators)

/function is permission level 2, so the editor is operator-only:

/function guikit:editor/open
/function guikit:help

1. Menu list — emerald creates a menu, a book opens it.
2. Editor chest — slots 0–25 are the menu. The bottom-right book is Tools (not part of the menu). Slot 26 of a real 27-slot menu is edited from Tools → Edit slot 26.
3. Hold the item you want as the icon, left-click a slot, pick an action in the dialog.
4. Tools: pages, rename, container, timeout, publish / hide, preview, delete.

Preview is the real menu. Chat suggests /function guikit:editor/resume to come back.

What a click can do

Click rules are on the slot dialog, after the action is placed. Keep leaves a rule as it is. Tags are not typed: an operator grants them with /tag <player> add vip (or member / staff). A button can have more than one rule. While a cooldown is running the icon is a barrier.

Other players

A menu cart follows its owner. While anyone else is within 8 blocks, a minecraft:interaction stands on the cart (wider and taller than a chest boat or minecart) and takes the right-click. It is not ridden: a passenger sits above the cart, and an interaction's hitbox only grows upward, so it would not cover the click.

• The other player gets “That menu belongs to another player.”
• The owner, if they click while someone is that close, gets “Someone is too close…”. The lock stays up until the other player steps away.
• Taking a widget out anyway does not run the action: each icon is stamped with the owner's id and stripped from anyone else.
• This does not kick a cart that is already open. Vanilla cannot close one player's chest without closing the owner's too. Stolen icons are deleted; the menu still times out.

Container presets: chest, hopper (5 slots), barrel, ender chest, trapped chest, shulker box, copper chest. Themed chests are still a chest_minecart with a different pane and title — Minecraft has no barrel entity to summon. A hopper menu only has slots 0–4; the editor marks the rest red.

Timeout is how long the menu stays open (15–180 seconds). The editor itself uses a long timeout so a dialog does not eat it.

Trust model

• Building menus requires /function (operator).
• Give / message / sound / page / toggle / counter do not run arbitrary commands.
• A command widget runs at datapack function permission (default 2), as the clicking player, for any player who can open the menu. Same trust as a command block behind a button. Do not put player-typed text in it. The command dialog rejects nothing by itself: do not put an apostrophe (') in the command, or the save line will not parse.
• Names, messages and lore must not contain " or \. Dialog text is escaped into the function call; the function stores it as a string and later shows messages with interpret:false.
• Menu ids are generated (m1, m2, …). Players never type them.

Backup / inspect:

/data get storage guikit:lib

How it is stored

storage guikit:lib
  order: ["m1", "m2"]
  menus.m1: {n, name, container, timer, published, pages:[{widgets:[...]}]}

guikit:reg is still rebuilt every /reload (that is the engine). Saved menus are registered again from guikit:lib by guikit:runtime/register. Do not data remove storage guikit:lib.

Per-player editor state is storage guikit:ed p<pid> and is not wiped on close, so a dialog can resume the editor.

Opening a menu from a command block

function guikit:play/open_id {menu:"m1"}

m1 is the generated id (/data get storage guikit:lib order).

Engine notes (advanced)

#guikit:register, #guikit:fill, #guikit:probe, #guikit:clear_tags and #guikit:on_close still exist and are not replace: true, so another pack can still add a listener. #guikit:on_open is new: it runs after the cart is bound and before the first redraw. The editor's fill/probe no-op unless this open set guikit:ed pending.

Widget helpers (guikit:widget/*) are what the editor draws with. Drawn icons also store own (the opener's uid) so a stolen stack can be stripped. Prefer the editor for new menus. A hand-written #guikit:fill pack still works beside it; do not clear guikit:lib from that pack.

Click detection is still “the widget item landed in the inventory”. clear is filtered by custom_data~{guikit:{w:1b}} and only runs after a count. See guikit:internal/selftest if a world wipes inventories — that bug was never proven.

Limits

• Not verified in a live 26.3 client. Load the pack and read latest.log. mecha is not a substitute; it does not validate macro lines.
• Editor slot 26 is the Tools button. The stored widget for slot 26 still shows in play / preview.
• Icons are item ids, not full stacks (no enchantments copied off the held item).
• Hopper menus: slots 5+ are not shown.
• Command widgets and links are macro-expanded. Quotes in a name, or an apostrophe in a command, fail that save instead of injecting a second command (vanilla has no command separator, but a broken macro line is still a failed save).
• Dialog buttons run as the player, so they need operator permission. That is why editing is /function and playing is a chest click / trigger.
• Two operators editing the same menu: last write wins.
• Donkey / mule containers are still registered by the engine and still refused (unchanged).
• The interaction lock is not a substitute for a live 26.3 test. F3+B shows the guard box while someone else is within 8 blocks.
• A player who already has the chest open when the guard appears is not force-closed. Do not kill the cart to kick them; that closes the owner as well.
• Click-rule tags are only vip, member, and staff. There is no free-typed tag.