How to Edit an Existing Block Entity's NBT with Autocomplete Help

Target the block and open its data

Stand near the block you want to modify and run /data get block ~ ~ ~ first to confirm you are pointing at the right one. The output shows the current NBT structure, which is a useful reference before you change anything. Then type /data merge block ~ ~ ~ { and let the mod suggest valid tags for that block entity type.

For a chest, you will see suggestions like Items, CustomName, and Lock. For a sign, you will see front_text and back_text with their nested messages lists. Pick the tag you want, insert it, and fill in the value. If you are adding items to a container, the mod will walk you through the Items list entry structure — Slot, id, and count — one key at a time.

Verify and revert if needed

After running the command, use /data get block ~ ~ ~ again to confirm the change took effect. If something looks wrong, you can overwrite the tag with a corrected value using another /data merge. To remove a tag entirely, use /data remove block ~ ~ ~ <tag> — autocomplete will suggest the tag names here too, so you do not have to retype the exact path.

This workflow is safe to repeat; each merge only touches the tags you name.