Tutorials – MCA Selector

How to Reduce Your Minecraft World Size with MCA Selector

Admin — Wed, 21 Oct 2026 15:10:34 +0000

Long-lived Minecraft worlds grow: every exploration session writes new chunks to disk forever, and most of them are terrain somebody flew over once. A bloated world means slow backups, slow uploads and slow restores. MCA Selector shrinks a world in two honest ways — deleting chunks that carry no value, and defragmenting the region files — and this guide shows both, plus how to measure the result yourself.

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.

Where world size actually lives

A Java Edition world stores its terrain in .mca region files: one file covers a 32×32-chunk region (512×512 blocks), and the Overworld, Nether (DIM-1) and End (DIM1) each keep their own set, alongside poi and entities data. World size is therefore driven by generated area: the further your players have explored in every direction — and the more dimensions they have opened — the more region files exist. There is no setting that shrinks that; you shrink it by removing area or by cleaning up the files themselves.

Method 1: Delete chunks nobody uses

The biggest wins come from chunks that were generated in passing. The recipe mirrors the reset workflow, minus the intent to revisit:

Open the chunk filter and match chunks with a very low InhabitedTime — terrain that was generated but barely spent time in.
Protect what matters first: build the selection of your bases and infrastructure, and use Subtraction mode (or a negated group) so the filter can never match them.
Apply the filter as a selection and look at it on the map before deleting — low InhabitedTime is a heuristic, and small outposts hide in it.
Export the selection as CSV for your records, then delete (Selection → Delete selected chunks). The freed space is real but the deletion is, as always, instant and permanent.
For whole areas nobody visits — a retired mining dimension, the far side of an exploration era — select and delete them wholesale, or prune them with the pruning workflow if they should regenerate fresh later.

Method 2: Remove an unused dimension entirely

If a dimension was generated by accident or for a one-off event — a few chunks of End, a test Nether — its whole folder can be removed in your file manager with the game closed: delete the dimension’s folder (DIM-1 for the Nether, DIM1 for the End, or the dimension folder of a datapack dimension) and Minecraft generates a fresh, empty dimension on the next visit. This is a file operation, not an MCA Selector feature, and the warning is absolute: everything in that dimension — Nether hubs, tunnels, End farms — is in that folder. Check twice, back up first, and if there is anything in the dimension worth keeping, delete selectively with the tool instead.

Method 3: Defragment the region files

Deleting chunks inside a region file can leave empty sectors behind — allocated space that no longer holds data. MCA Selector’s Defragment function rewrites the region files without those gaps, compacting what remains. It does not change a single chunk’s contents; it simply stops the files from carrying the holes left by earlier deletions. Run it after a big deletion pass, on the same backup discipline as everything else in this tool.

Measure the result yourself — no magic numbers

Any honest size guide ends with measurement, not promises, because the outcome depends entirely on how much dead terrain your world carries. Before you start, note the world folder’s size on disk (folder properties in your file manager). Repeat after each method. A world that is 90% lived-in bases will barely shrink; a world with years of fly-over exploration can shrink dramatically. Beware any guide — including older versions of this website — that quotes a specific before/after size for your world: nobody can know that number but your file manager.

Verify, then enjoy the smaller backups

Open the trimmed world in Minecraft and visit your bases, farms and portals in every dimension you touched. Confirm the areas you meant to keep are untouched, then take a fresh backup of the slimmed world — the routine this whole exercise was for: smaller backups, faster server uploads, cheaper storage. Then go back to the complete guide for the rest of what the tool can do.

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.

Related guides

How to Prune a Minecraft World in MCA Selector Before an Update

Admin — Wed, 21 Oct 2026 15:10:16 +0000

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.

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

Related guides

MCA Selector Selection Tools: Select, Invert & Save Selections

Admin — Wed, 21 Oct 2026 15:09:55 +0000

Every operation in MCA Selector starts with a selection, so the selection tools repay learning properly. This guide covers all of them: rectangle and brush selection, the chunk/region mode switch hidden in the zoom level, Invert and Clear, the Add and Subtraction modes, and saving selections to CSV so a careful selection never has to be built twice.

Two selection modes, decided by zoom

The most important selection “tool” is not a tool at all: it is the zoom level. Zoomed in, the map shows the chunk grid and you select individual chunks of 16×16 blocks. Zoomed out, the grid becomes regions of 32×32 chunks (512×512 blocks) and every click or drag selects whole regions. Switching happens automatically as you zoom — which is convenient, and also the number-one cause of accidental mass deletions. Build the habit: before any destructive operation, glance at the grid and say which unit you are selecting in. The delete chunks guide shows where this bites.

Rectangle and brush selection

Click selects a single chunk (or region, at region zoom).
Drag draws a rectangle — the natural way to mark a base, a city district or a cleanup zone.
Shift + mouse paints with a brush: hold Shift and move across the map to add chunks in a free-form shape, which is how you trace coastlines, rivers and irregular build footprints that a rectangle would overshoot.

Invert and Clear

The Selection menu holds the two housekeeping operations. Invert flips the selection to everything except what you had — the foundation of the “keep this, delete the rest” workflows behind world pruning: select your bases carefully, invert, and the deletion candidate is everything else. Clear empties the selection so you can start fresh without reopening the world. After using Invert, re-check the map before deleting — deleting the inverse of your intent is the classic own goal.

Building selections up: Add and Subtraction modes

Complex selections are assembled, not drawn in one gesture. When you import a selection or apply a filter, you choose how the incoming chunks combine with what you already have:

Mode	Effect
Add Selection	The incoming chunks are added to the current selection (the union).
Subtraction	The incoming chunks are removed from the current selection — carving protected or excluded shapes out of a bigger selection. Subtraction mode arrived in MCA Selector 2.7 and applies both to selection imports and to filters.

A typical assembly: drag one big rectangle around a city, then subtract the rectangle of the one player’s plot that must not be touched, then add back a small outlying farm by hand. Three simple operations, one precise selection.

Saving selections to CSV

A selection disappears when you close the tool — unless you save it. Selection → Export selection writes the selection to a CSV file; Selection → Import selection reads one back, combining it with the current selection via the Add or Subtraction mode above. CSV selections earn their keep in three situations:

Documentation — the CSV is the exact record of what a cleanup deleted; file it with your world backup.
Repetition — recurring maintenance (monthly resets of a mining dimension, for example) reuses the same protected-area selection instead of redrawing it.
Rehearsal — build the selection once, save it, then run the whole operation on a backup copy first; if the rehearsal passes, import the same CSV and run it on the real world. (The complete guide walks through this pattern.)

Selection discipline, in one list

Confirm the zoom/mode unit before you start, and again before anything destructive.
Prefer assembling (add + subtract) over heroic single drags.
Export important selections to CSV before you use them.
After Invert, look at the map — the highlighted area is what the next operation will touch.

Download MCA Selector 2.9

Related guides

MCA Selector Chunk Editor: Edit One Chunk’s NBT by Hand

Admin — Wed, 21 Oct 2026 15:09:37 +0000

Most of MCA Selector works on thousands of chunks at once. The Chunk Editor is the opposite: a tree editor for the raw NBT data of exactly one chunk — its terrain data, its points of interest and its entities. It is the microscope you reach for when you need to see, or surgically fix, what is actually inside a chunk.

Opening the Chunk Editor

Select exactly one chunk on the map (zoom in to chunk mode first) and open the editor with Ctrl+B. With zero or multiple chunks selected it will not open — that single-chunk restriction is by design, because the editor shows the complete NBT structure of the region, poi and entities data for that one chunk. If your change needs to happen in many chunks at once, that is the NBT Changer’s job, not this editor’s.

What you are looking at

The editor presents the chunk’s data as an expandable NBT tree: named tags holding numbers, strings, lists and nested compounds, including an array editor for the long array values chunk data is full of. You can add, delete and modify tags. Two habits make this safe rather than scary:

Read before you write. Spend the first session just exploring a chunk from a throwaway world, so the structure is familiar before anything depends on it.
Change one thing at a time. A single edited value, verified, beats a heroic multi-tag rewrite you cannot bisect when the chunk misbehaves.

Apply: the one place MCA Selector waits for you

Here is the difference that matters most. Deletes, filter operations and the NBT Changer write to disk the moment they run. The Chunk Editor does not: your edits live in the editor until you press Apply, and only then is the modified chunk data saved to disk (discarding the editor without Apply throws the edits away). This cuts both ways:

It is the one workflow where “I changed it but nothing happened in game” usually means Apply was never pressed — the most common Chunk Editor support question, with the simplest fix.
It is also a genuine safety net: you can inspect and stage a risky edit, and back out without touching the world — the only place in the tool where that is true. Your backup is still required, because once Apply is pressed, the write is final.

Good uses for the Chunk Editor

Diagnosing what a chunk actually contains — which DataVersion it carries, whether a field the filter relies on is present, what its biome palette holds (the background to the biome guide).
One-off repairs: a single corrupted or wrong value in a known chunk.
Verifying batch work: after an NBT Changer run on a test selection, open one edited chunk here and confirm the field really changed the way you intended, before scaling the run up.

A safe editing session

Back up the world; rehearse on a copy if the chunk matters.
Open the world, zoom to chunk mode, click the one chunk, press Ctrl+B.
Find the tag, make the smallest edit that expresses your change.
Press Apply.
Close the tool, open the world in Minecraft, and check the chunk in game — including its neighbours, since chunk borders are where bad edits show first.

Download MCA Selector 2.9

Related guides

MCA Selector NBT Changer: Batch-Edit Chunk Data

Admin — Wed, 21 Oct 2026 15:09:15 +0000

The NBT Changer is MCA Selector’s batch editor: pick chunks, pick fields, and the tool rewrites those fields in every selected chunk in one run. It is how you fix a thousand chunks’ DataVersion, flatten biomes, strip entities or force terrain blending without opening a single chunk by hand — and because it writes straight to disk, it deserves respect.

What the NBT Changer can change

Field	What it does
`DataVersion`	Rewrites the version stamp of the chunks. It changes the number, not the chunk data format — see the warning below.
`InhabitedTime`	Rewrites how long the chunk counts as inhabited — used when preparing chunks for regeneration logic or correcting filter results.
`Biome`	Sets the entire chunk to a single biome — the subject of the change biome guide.
`ReplaceBlocks`	Replaces one block with another, by name, across all selected chunks.
`DeleteEntities`	Removes entities from the selected chunks.
`DeleteSections`	Deletes vertical sections (16-block slices) from the chunks.
`FixStatus` / `FixHeightmaps`	Repairs the generation status field / recalculates heightmaps.
`DeleteStructureReference`	Removes structure references from the chunks.
`PreventRetrogen`	Marks chunks so the game does not try to retro-generate features into them.
`ForceBlend`	Forces the terrain blending used at borders between chunks generated by different generators — meaningful mainly around the 1.18 terrain overhaul; on chunks where those conditions do not apply it visibly does nothing.
`RemoveLightingInfo`	Strips stored lighting data so the game recalculates it (the field itself was added in MCA Selector 2.9’s update round).
`Compression`	Changes how the chunk data is compressed in the region files.
`Custom`	A Groovy script that can read and rewrite chunk data with full logic.

Change vs Force — the two modes

Each field can run in one of two modes. Change only modifies the field where it already exists in the chunk data. Force writes the field even where it is missing. Change is the conservative default: if a chunk does not carry the tag, it is left alone. Reach for Force when you specifically need the value present everywhere — and understand that “everywhere” will then really mean everywhere in your selection. You can also restrict a run to the current selection only, which you should treat as the default discipline: select first, change second, exactly as with the chunk filter.

A safe run, step by step

Back up the world. Then copy it, and rehearse on the copy.
Select a small test set — a handful of chunks, not the whole world.
Open the NBT Changer, set one field only, choose Change mode, limit to the selection.
Run it, close the tool, and inspect the result: in game, and if you want the raw truth, in the Chunk Editor on one of the edited chunks.
Only when the test set behaves do you widen the selection to the real target area.

Groovy scripts: power with a blast radius

The Custom option runs a Groovy script against each chunk, giving you programmatic access to the chunk data — the same scripting support the filter dialog offers. Scripts are the way to do things like per-section biome palette edits that the single-value Biome field cannot express. They are also unforgiving: a script bug applies at the same speed as a correct script. Write defensively, test on a copy, and keep the script file with your backup so the change stays reproducible.

The DataVersion warning, plainly

Because DataVersion sits in the field list, it is tempting to “convert” chunks between game versions by renumbering them. Do not. The field is metadata the game uses to decide how to parse and upgrade the chunk; rewriting it does not transform the chunk’s contents. Mismatched DataVersion and content is a reliable route to chunks that fail to load or upgrade wrongly. Legitimate uses exist (repairing a stamp that is genuinely wrong), but version conversion is the game’s job when it loads a chunk, not the NBT Changer’s.

Download MCA Selector 2.9

Related guides

MCA Selector Filters: The Chunk Filter & Query Guide

Admin — Wed, 21 Oct 2026 15:08:57 +0000

Selecting chunks by hand works for a village. It does not work for “every chunk this world generated before 1.20” across a 40,000-chunk world. That is what the chunk filter is for: you describe the chunks you want with conditions — DataVersion, InhabitedTime, biome, entities and more — and MCA Selector builds the selection (or deletion) for you.

What the filter can match

The filter dialog combines conditions on the fields MCA Selector reads from each chunk, including:

Field	Typical use
`DataVersion`	Find chunks generated by a specific Minecraft version range — for example everything older than your current version, before a prune. The DataVersion list gives the numbers per version.
`InhabitedTime`	How long players have spent in the chunk, in game ticks (72,000 = one hour). Low values = fly-over terrain; the basis of safe chunk resets.
`xPos` / `yPos` / `zPos`	The chunk’s own coordinates — limit an operation to a boxed area of the world.
`Biome`	Chunks containing (or set to) a given biome.
`Palette`	Chunks containing a given block — find every chunk that has a particular block in it.
`Status`	How far the chunk progressed through generation — useful for finding partially generated chunks at world borders.
`Entities` / `#Entities`	Chunks containing a named entity type, or more than a chosen number of entities — a first stop for entity-lag hunts.
`Structures`	Chunks holding a structure reference.
`PlayerLocation`	Chunks near where players are (or were) located.
`Timestamp` / `LastUpdate`	When the chunk was last written/updated.
`Circle` / `Border`	Geometric conditions — a radius around a point, or chunks at the edge of the generated area.

Combining conditions: groups and NOT

Conditions can be stacked, and the filter offers Group and Not Group to structure them: a group bundles several conditions so they are evaluated together, and negating a group excludes everything inside it. In practice that lets you express the queries that matter, such as:

“DataVersion below the current version’s range and InhabitedTime under 36,000″ — old, barely visited chunks: prime reset/prune candidates.
“Not (inside the rectangle around spawn and the bases)” — build a protected zone as a group, negate it, and every other condition only applies outside it.
“Palette contains minecraft:diamond_ore“ — a novelty query that also demonstrates the Palette field reads real block data, not just metadata.
“#Entities above 500” — find entity-crammed chunks before they become a performance ticket.

What the filter does with the matches

A filter run has two kinds of outcome. It can build a selection — including adding matches to an existing selection (Add Selection) or cutting matches out of it (Subtraction mode) — so you can review the highlighted chunks on the map before deciding anything. Or, in its delete mode, it can delete every matching chunk directly. The official documentation’s wording for that mode deserves quoting: all chunks matching the filter are deleted in the original files, and “this operation is instant and there is no going back.” Prefer the selection outcome on a first pass; delete only after you have seen what matched.

The second tab: Groovy script filters

Next to the condition builder, the filter dialog has a tab for a Groovy script filter: a script that is evaluated per chunk and decides with full logic — comparisons across fields, string matching, arithmetic — what the condition list cannot express. Scripts are also the engine behind the custom changes in the NBT Changer. Treat scripts like code, because they are: develop them on a copy of the world, log what they match, and only then run them on the real save.

A repeatable workflow for big cleanups

Back up the world; work on the real save only after a rehearsal on the copy.
Start with a narrow query (one condition) and apply it as a selection. Does the highlight match what you expected?
Tighten with a second condition or a Not Group protecting your bases.
Export the final selection as CSV (Selection → Export selection) so the exact cleanup is archived.
Run the destructive step — deletion, or hand the selection to the pruning workflow in prune a world for an update — then verify in game.

Download MCA Selector 2.9

Related guides

How to Export and Import Chunks with MCA Selector

Admin — Wed, 21 Oct 2026 15:08:38 +0000

Exporting and importing is how you move a castle, a city district or a whole spawn area from one world into another — or archive a build as standalone chunk files. MCA Selector handles both directions: exports write a portable chunk package, imports merge chunks into a target world with control over exactly where they land.

Exporting chunks

Open the source world (File → Open World) with Minecraft closed.
Select the chunks to export — drag a rectangle around the build, and zoom in to check the edges chunk by chunk. Remember that entities and points of interest are stored alongside the terrain, so include every chunk the build touches.
Choose Selection → Export selected chunks and pick an empty target folder.
MCA Selector writes new region, poi and entities folders into it. The source world is not modified — exporting is the one operation in this tool that is safe by design.

There is also an Export as image option that renders the selection as a picture — handy for sharing a map of an area, useless for moving builds. Keep the two apart.

Importing chunks into another world

Open the target world first (File → Open World). Importing always merges into the world that is currently open — opening the source world instead is the classic mistake.
Choose Tools → Import chunks and point it at the folder you exported earlier (the folder containing the region/poi/entities folders).
Set the placement options (next section), review them, and run the import.
Close the tool and check the result in game before you do anything else.

A lighter-weight alternative for small moves is copy and paste: select chunks, copy with Ctrl+C, open the other world, and paste with Ctrl+V. The full import dialog is the better tool when placement has to be precise.

Placement: Offset, Y-Offset, sections and Overwrite

Option	What it does
Offset	Shifts the imported chunks by a number of chunks on the X/Z axes. The unit is chunk coordinates — block coordinates divided by 16. An offset of 10 moves the build 160 blocks.
Y-Offset	Shifts the import vertically, counted in sections of 16 blocks. Use it when the build was made at a different height than the target terrain.
Sections range	Limits which vertical sections (16-block slices) are taken from the source chunks.
Overwrite	Whether imported chunks replace the target chunks already at that position. Without overwrite, existing chunks in the way are left alone — check the result either way.
Apply to selection only	Restricts the import to the chunks inside your current selection in the target world.

Work out the offset on paper before you import: find the chunk coordinates of the build in the source world (block X ÷ 16, block Z ÷ 16), decide where its corner should land in the target world, and the difference is your offset. The selection tools guide shows how to read and re-create exact selections with CSV files, which pairs well with imports you may need to repeat.

Version and DataVersion compatibility

Imported chunks keep the DataVersion they were saved with. If they come from a newer Minecraft version than the target world runs, the game may fail to load them or convert them unpredictably — match versions, or upgrade the target world, rather than forcing newer chunks into an older game. The DataVersion list maps values to game versions.
Chunks from an older version generally load and get upgraded by the game on first visit, like any old world.
Changing the DataVersion field with the NBT Changer only rewrites the number — it does not convert the chunk’s contents to another version’s format. Do not use it to “downgrade” chunks.

Two things that do not travel with the chunks

The official documentation is explicit about two gaps: commands inside command blocks are not changed (coordinates inside commands still point at the old location), and maps are not updated, because map data is not stored inside the region files. Budget time to fix command blocks by hand and to re-create maps after a move, and check anything position-dependent — redstone with absolute coordinates, structure blocks, spawn points — in game.

Download MCA Selector 2.9

Related guides

How to Change a Chunk’s Biome in MCA Selector

Admin — Wed, 21 Oct 2026 15:08:19 +0000

Want a plains base in a desert, or a frozen harbour where the game generated a warm ocean? MCA Selector can rewrite a chunk’s biome — with one important limitation you need to understand first: in the current tool, a biome change applies to the whole chunk at once. There is no biome brush. Here is the exact path, and what to do when a whole chunk is too coarse.

The tool for the job: the NBT Changer’s Biome field

MCA Selector changes biomes through the NBT Changer, its batch NBT editor. Among its fields is Biome, which sets the biome of every selected chunk to a single value. The workflow:

Open the world (game closed) and select the chunks whose biome you want to change — by dragging on the map, or by filter if you want, say, only chunks currently of a certain biome.
Open the NBT Changer and find the Biome field.
Enter the target biome by name or ID (for example minecraft:snowy_plains). A custom biome from a datapack or mod is entered in single quotes.
Make sure the change is limited to your selection if you do not want it applied more widely, then run it.

Like almost everything in MCA Selector, the change is written to the world files as soon as it runs — no Save step, no undo. If you are new to the NBT Changer, the NBT Changer guide explains its Change vs Force modes and its other fields before you touch a real world.

What a whole-chunk biome change does and does not do

It changes the biome data — grass and leaf colours, precipitation (rain vs snow), ambient effects and biome-dependent spawning rules follow the new biome.
It does not change a single block. Sand stays sand and water stays water; only the biome label changes. Reshaping the terrain itself is a different job (delete and regenerate, or edit in game).
It is all-or-nothing per chunk. A chunk that straddles a riverbank gets one biome everywhere, including the parts that looked right before.
Already-generated structures and features stay. Changing a chunk to a biome does not retroactively add that biome’s structures.

Finer control: per-section changes need a script

Under the hood, a chunk stores biomes per 16-block-tall section, in a biomes palette. The NBT Changer’s single Biome field deliberately collapses that to one value. If you truly need different biomes in different sections of a chunk, the official route is a Groovy script in the NBT Changer’s custom/script support that rewrites the sections’ biome palettes directly — the official wiki’s custom filter tutorial shows the pattern. That is power-user territory: test any script on a throwaway copy of the world first, on a handful of chunks, and check the result in game before running it widely. The single-chunk Chunk Editor is the other manual option for inspecting what a chunk actually contains.

Verify the change

Open the world in Minecraft and go to the edited chunks.
Press F3 and read the biome shown on the debug screen while standing in the chunk — it should report the new biome.
Check the visible tells: grass colour, and whether precipitation and foliage match the new biome.
Walk across the chunk border to confirm neighbouring chunks were not changed by accident.

If the F3 screen still shows the old biome, the usual causes are that the change was applied to a different selection than you thought, or the world was open in the game while you edited and overwrote it — close everything, restore the backup, and redo it on the copy first.

Download MCA Selector 2.9

Related guides

How to Reset Chunks in MCA Selector

Admin — Wed, 21 Oct 2026 15:08:01 +0000

“Resetting” a chunk in Minecraft means deleting it so the game generates it again from scratch — with the terrain, ores and structures of the version you are running now. It is how old worlds get new-update caves, ores and biomes without starting over. MCA Selector does not have a separate reset button: a reset is a delete with a plan, and this guide is that plan.

How resetting works

A chunk exists on disk only because it was generated and saved. Delete it in MCA Selector and the next time a player enters that area, Minecraft generates a brand-new chunk from the world seed using the current version’s generator. Three consequences follow:

Everything in the chunk is gone: builds, chests and their contents, containers, entities that were saved with it.
The new chunk matches the current game version — new ores, caves and structures can appear.
The new chunk may not blend smoothly with the old terrain around it; expect visible borders on dramatic generation changes.

Step 1: Decide what is safe to reset

The workhorse for this is the InhabitedTime field: how long players have spent in a chunk, stored in game ticks (20 ticks = 1 second, so one hour in a chunk is 72,000). Chunks a player merely flew over on the way somewhere typically show a tiny InhabitedTime; chunks containing bases, farms and storage show a large one. Resetting low-InhabitedTime chunks refreshes the exploration filler around your world while leaving lived-in areas untouched. It is a heuristic, not a guarantee — a chunk can hold a small outpost a player built in ten minutes — so combine it with a look at the map.

Step 2: Select the chunks to reset

Open the world (File → Open World) with the game and server closed.
Open the chunk filter and set a condition on InhabitedTime — for example, only chunks below a threshold you choose based on how your players actually play (start conservative).
Optionally add a DataVersion condition so you only touch chunks generated by older game versions; the DataVersion list shows which values belong to which Minecraft version.
Apply the filter to build the selection, then zoom in and eyeball the borders of the selection near your bases before deleting anything.
Export the selection (Selection → Export selection) as a CSV so the reset is documented and repeatable.

Step 3: Delete, then let the game regenerate

Run Selection → Delete selected chunks. Deletion is instant and permanent — there is no separate “regenerate” step inside MCA Selector. Regeneration happens later, in Minecraft, when someone loads the area. The mechanics are the same as the delete chunks guide; if you are resetting everything outside your kept areas for a major update, the pruning workflow wraps this into a complete procedure.

Protect these areas — a pre-reset checklist

Main bases, storage systems and farms in every dimension you edit — check Overworld, Nether (travel hubs and tunnels are easy to forget) and End separately.
Spawn point surroundings and any spawn builds.
Community areas on servers: shops, mini-game arenas, other players’ projects.
Chunks containing portals your players rely on — the portal in the other dimension can end up orphaned.
Anything marked on maps or in screenshots that you cannot locate on the MCA Selector map — find it first, reset later.

Step 4: Verify in game

Load the world, visit a reset area, and confirm the new terrain generates with the expected features of your current version. Check the seams around kept areas. If something important was reset, restore the backup copy — which is why the backup from the top of this guide is not optional.

Download MCA Selector 2.9

Related guides

How to Delete Chunks in MCA Selector (Step by Step)

Admin — Wed, 21 Oct 2026 15:07:41 +0000

Deleting chunks is the core job of MCA Selector: clear old terrain so it regenerates, remove corrupted chunks, or strip a world down to the parts players actually use. The operation itself is three clicks — the skill is in selecting exactly the right chunks, because deletion is instant and cannot be undone.

Step 1: Open the world and pick the right selection mode

Choose File → Open World and select the world folder (the one directly containing region/poi). Then zoom: zoom in until you see the chunk grid if you want to delete individual chunks, or zoom out to the region grid if you deliberately want to delete whole regions. This is the mistake behind most “I deleted too much” stories — at region zoom, a single drag can mark 1,024 chunks per region square. The map grid on screen always tells you which mode you are in.

Step 2: Select the chunks to delete

Click or drag to select single chunks, hold Shift to paint a free-form area. Use Selection → Invert if it is easier to mark what you want to keep and delete the rest, and Selection → Clear to start over. To select by properties instead of by hand — for example every chunk with an old DataVersion — use the chunk filter, which can apply the same deletion to every chunk matching your conditions. Before deleting, consider Selection → Export selection to save the selection as a CSV record of what you are about to remove. The selection tools guide covers all of this in depth.

Step 3: Delete — it happens immediately

Choose Selection → Delete selected chunks and confirm. That is the whole procedure, and it is also the point of no return: as the official documentation puts it, chunks are deleted in the original files, “this operation is instant and there is no going back.” There is no recycle bin, no undo, and no File → Save step afterwards — the chunks are already gone from disk when the dialog closes.

Step 4: Verify the result

Close MCA Selector, then open the world in Minecraft.
Fly to the area you edited. Deleted areas appear as void until you enter them.
Walk or fly into the cleared area so the game regenerates it, and check the borders between deleted and kept chunks for cliffs or cut-off builds.
Only now — once the world checks out — delete your safety backup, or keep it until the next backup cycle.

Deleting a whole dimension or old regions

Everything above works per dimension: open the world, switch to the dimension you want to edit, and repeat. For bulk cleanups tied to a game update — deleting everything except your bases so new terrain generates — follow the dedicated world pruning workflow, and if your goal is fresh terrain in specific spots rather than removal, the reset chunks guide explains the regenerate-after-delete mechanic.

Mistake-proofing checklist

Minecraft and any server using the world are fully closed.
You have a dated backup copy of the whole world folder.
The zoom level matches the selection unit you intend (chunks vs regions).
The selection — not its inverse — is what gets deleted; re-check after using Invert.
You exported the selection to CSV if the cleanup is large or hard to re-create.