Illegal Placement

Place blocks in states vanilla won't let you — a lever in mid-air, half a bed, a fence that connects to nothing — and keep them that way. No commands needed: press B, aim, click.

The server needs the mod. In singleplayer the client is enough. Fabric builds need Fabric API (any version for your Minecraft version).

Build mode

All keys are rebindable.

The panel

Every block state property on a button: left click for the next value, right click for the previous. Two switches underneath:

• Lock state — the block ignores shape updates, neighbor updates and survival checks. It stays exactly as placed.
• Freeze time — no random or scheduled ticks: no falling, growing, decaying, spreading.

Item frames, paintings and armor stands get a panel too (Fixed, Invisible, ShowArms, Facing, …).

In build mode the outline of the aimed block shows what the next update would do to it: orange means it would drop, be reshaped or switched by redstone — lock it if it should stay. Green means it's locked.

Litematica on servers

Set commandNameSetblock = ipsetblock and commandNameFill = ipfill in Litematica's settings. Pastes then keep every illegal state, lock what needs locking and freeze what would fall.

Config

config/illegalplacement-server.properties: permission level, creative only, max reach, fill volume. Client options are in the Build Settings screen (press G while aiming at air).

Known limitations

• Freeze time doesn't stop block entities (furnaces, hoppers).
• Display entities and markers can't be targeted.
• Since 1.21.6, G is also vanilla's Quick Actions key; both work.