A major Minecraft update lands — new terrain, new structures, new ores — and your old world has millions of already-generated chunks locking the new content out. Pruning is the fix: delete the chunks nobody uses so they regenerate with the new generator, while the chunks containing your builds stay exactly as they are. This is the complete MCA Selector workflow, from first backup to in-game verification.
Back up your world first: MCA Selector writes deletions and NBT changes straight to disk the moment you confirm them — there is no undo and no File → Save step to catch a mistake. Close Minecraft (and stop your server, if the world is on one), then copy the whole world folder somewhere safe before you edit.
What pruning can and cannot do
Pruning deletes chunks; regeneration is done by Minecraft, from the world seed, with your current game version, the next time the area is loaded. Kept chunks keep their old terrain and old DataVersion — pruning does not upgrade them — and new chunks may meet old ones at visible seams. That trade is the whole point of the technique, and it is why what you keep matters more than what you delete.
Step 1: Inventory what must survive
Before opening the tool, list the areas that are non-negotiable, per dimension: every player’s base, storage, farms, spawn builds, community projects, Nether hubs and tunnel networks, End gateways’ surroundings. Note their approximate coordinates (press F3 in game, or check your map screenshots). This list becomes your protected selection — a forgotten Nether hub is the prune story everyone tells afterwards.
Step 2: Build the “keep” selection
- Open the world with the game and server closed (File → Open World).
- Zoom to chunk mode and drag rectangles generously around each area on your inventory list — include a margin of a few chunks around builds so borders do not slice through landscaping.
- Use Add Selection to accumulate the areas and Subtraction to carve back overshoots; the selection tools guide covers the mechanics.
- Export the keep-selection as CSV (Selection → Export selection). This file is your insurance policy and your documentation in one.
Step 3 (optional but recommended): narrow with a filter
Deleting everything outside the keep-selection is the aggressive option. A gentler prune deletes only chunks that are both unprotected and barely used: invert the keep-selection, then use the chunk filter in Subtraction mode to remove from the deletion set every chunk with a meaningful InhabitedTime, or add a DataVersion condition so only chunks generated by older versions are deleted while newer explored terrain survives. The reset chunks guide explains the InhabitedTime logic in detail.
Step 4: Invert and delete
- If you did not use the filter route: with the keep-selection active, choose Selection → Invert — the selection is now “everything except what you keep”.
- Look at the map. The highlighted area is what is about to be deleted. Check the borders around each kept area one more time.
- Run Selection → Delete selected chunks and confirm. This is instant and irreversible; the backup from step 0 is the only way back.
- Repeat per dimension if you are pruning the Nether or End as well — each dimension is edited separately.
Step 5: Verify, and mind the borders
Open the world in Minecraft on the new version and fly the borders between kept and regenerated areas. New terrain will differ in height and style from old terrain; for the seams left by the 1.18-era terrain overhaul, the NBT Changer’s ForceBlend field exists to force blending at borders between chunks from different generators — the NBT Changer guide explains what it does and when it has no effect. Check your protected list one final time in game, then archive the backup and the CSV together.
When not to prune
- The world is actively played and you have no verified backup — wait until you do.
- Your “keep” inventory is guesswork. Walk the world (or the map) first.
- You actually want the new content inside explored areas too — pruning only refreshes deleted chunks; a new world or targeted resets may be the better answer.
Download MCA Selector 2.9
Everything in this guide works with the current release. Get the Windows installer, the cross-platform .jar, the macOS .dmg or the Linux .deb/.rpm from the MCA Selector download page — every button there points at the official GitHub release files and lists the SHA-256 checksum, with a clearly labelled site mirror as a fallback.
One last backup reminder: keep the copy of your world you made before editing until you have loaded the edited world in Minecraft and confirmed it looks right. Deletions and NBT changes in MCA Selector are permanent once applied.