It is an in-game block-ID inspector tool for Hytale creators, exposed through an offhand utility item and a simple popup UI.

How to Use Block Inspector

Notes

The inspector reads the main-hand item, not the offhand.

The main-hand item must be a block item.

If your main hand is empty or not a block, nothing will be returned.

The popup is purely for viewing and copying the ID.

Offhand: Block Inspector
Main hand: Stone Block
Press Ability 1 → Popup shows something like:

hytale:stone