Troubleshooting – MCA Selector

MCA Selector Mac Problems: Won’t Open or Install

Admin — Wed, 21 Oct 2026 15:21:31 +0000

“MCA not working on Mac” (issue #348) is one of the most discussed threads in the project’s history — and also one of the most outdated. Most of the advice in old threads describes wrestling a bare .jar plus a hand-installed JavaFX on macOS. That route is obsolete: there is an official Mac package now, and starting there fixes the majority of cases.

The current way to install on Mac

Download the macOS .dmg that matches your chip from the download page: arm64 for Apple Silicon (M-series) Macs, x64 for Intel Macs. These official .dmg packages have existed since MCA Selector 2.8; the current release is 2.9.
Open the .dmg and install the app as you would any other.
Launch it. Because it is a self-contained app, you do not need to install Java or JavaFX separately for the packaged build.

Our full walkthrough, including how to tell which chip your Mac has, is the MCA Selector for Mac install guide.

If macOS refuses to open it (Gatekeeper)

macOS Gatekeeper can block apps that did not come from the App Store, sometimes with a warning that the app “cannot be opened” or is damaged — wording that sounds worse than it is. The standard way through it:

Instead of double-clicking, right-click (or Control-click) the app and choose Open. macOS then shows the same warning but with an Open button — confirming once is usually enough for future launches.
If there is no Open button, go to System Settings → Privacy & Security, scroll to the note about the blocked app, and choose Open Anyway.
Only do this for the genuine package: verify you got the .dmg via our download page, which links the official GitHub release and lists its SHA-256 checksum.

If you are following an old guide that uses the .jar

Old threads (including much of #348) assume the universal .jar plus a manually installed JavaFX. On macOS that combination fails in exactly the ways those threads describe — missing-JavaFX dialogs and silent launches — and debugging it is no longer worth your time now that a native package exists. Switch to the .dmg for your chip first; keep the .jar route only if you specifically need it, in which case our Missing JavaFX guide has the official module-path launch command.

If it still does not work

Confirm the two basics first: the .dmg matches your chip (an x64 build on Apple Silicon, or vice versa, causes exactly this class of failure), and you are on the current version rather than an old download. If both are right, open the world folder check from our No Dimensions Found guide if the app opens but the world will not — that error is about folder selection, not about Macs. For install failures beyond that, issue #348 on the official tracker is the thread to read and add your macOS version and chip to.

Get the Current Version First

Several of the problems in this guide disappear on the current release. MCA Selector 2.9 is free and open source — get the Windows installer, the cross-platform .jar, the macOS .dmg or the Linux .deb/.rpm from the MCA Selector download page, where every button points at the official GitHub release files with their SHA-256 checksums.

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This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector ‘Open World’ Does Nothing? Check the Saves Path

Admin — Wed, 21 Oct 2026 15:21:12 +0000

You click File → Open World in MCA Selector and… nothing. No file dialog, no error, no freeze — the menu item simply does nothing. This is issue #466 on the official tracker, and unusually for a silent failure, its cause is known and the fix takes a minute.

Why it happens

MCA Selector remembers a saves directory in its Settings — the folder the Open World dialog starts in. If that folder no longer exists (you moved your Minecraft installation, deleted the folder, changed drives, or the setting was carried over from another machine), the dialog has nowhere to open and silently gives up instead of showing an error.

Fix it step by step

Open MCA Selector’s Settings.
Find the saves directory setting and check the path it points to.
Open that exact path in your file manager. If the folder is not there, you have found the problem.
Set the saves directory to a folder that actually exists — normally the saves folder inside your .minecraft directory, the one that directly contains your world folders.
Save the settings and try File → Open World again. The dialog should now appear, starting in the folder you just set.

Related symptoms this also explains

The dialog opens but starts in a strange, empty folder — same setting, same fix.
Your worlds “disappeared” from the dialog after reinstalling Minecraft or moving to a new PC — the setting (or the installation) now points somewhere else; your saves themselves are wherever the game actually stores them.
Once the dialog works, selecting the folder can still fail with “No Dimensions found” if you pick the wrong level — that is a separate issue with its own guide: No Dimensions Found causes and fixes.

If it still does not work

Issue #466 is still open upstream, so treat the steps above as the community-known workaround rather than an official patch. If your saves path definitely exists and Open World still does nothing on the current version (2.9), launch the tool from a terminal (java -jar mcaselector-2.9.jar), click Open World, and add whatever the terminal prints to issue #466 — silent failures only get fixed when someone captures what the program was trying to do.

Get the Current Version First

More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector Crashes or Freezes When Loading a World

Admin — Wed, 21 Oct 2026 15:20:53 +0000

You point MCA Selector at a world and it crashes, freezes, or hangs while loading — sometimes before the map even appears. The best-known report of this is issue #299, where a 1.17.1-era tool froze trying to load a 1.18 world, and the pattern behind it still explains most cases today.

The main cause: the tool is older than the world

Minecraft’s world format evolves with every game update, and MCA Selector has to be updated to understand each new one. The support window is defined by DataVersion: the current MCA Selector 2.9 covers worlds up to Minecraft 26.3 (DataVersion 5023+), but an older tool build simply cannot parse chunks written by a newer game — and failing to parse them can mean a freeze or a crash rather than a tidy error message. Our DataVersion list shows which values belong to which game version, and our version history shows which MCA Selector release added support for what.

Fix it step by step

Check your MCA Selector version (title bar / About) against the current release. If your world was last saved by a recent Minecraft version, update MCA Selector first — for 26.x worlds you need the 2.7+ line, and for 26.3 worlds you need 2.9.
Close Minecraft completely before opening the world in MCA Selector; a world that is open in the game (or on a running server) is mid-flight and not safe to read or edit.
Try opening a different, freshly created world. If that loads fine, your installation is healthy and the problem is specific to the first save; if every world crashes the tool, suspect the installation or its Java runtime instead (see our not-opening guide).
If one specific world fails while others load, work on a copy of it: restore its region files from your most recent backup into the copy and test again. A world that used to load and suddenly does not, where only some saves are affected, is the basic fingerprint of damaged files in that save — the backup copy is the fix, not a repair utility.

A special case: snapshot worlds

If the world was played in a Minecraft snapshot, temper your expectations: the official README states plainly that there is no guarantee snapshot worlds work and that old snapshots are not supported. Snapshot formats can change between weekly builds in ways no external tool can fully track. Your realistic options are to wait for (or update to) an MCA Selector release that catches up, or to edit the world after it has been opened and re-saved by the matching release version of Minecraft.

If it still does not work

Launch the tool from a command line (java -jar mcaselector-2.9.jar) and open the world again — the stack trace printed when it fails is exactly what the upstream tracker needs. Search the Querz/mcaselector issues for your MCA Selector version plus your world’s Minecraft version before posting, and include the trace, both version numbers, and whether other worlds load.

Get the Current Version First

More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector Only Deletes Whole Regions? It’s the Zoom Level

Admin — Wed, 21 Oct 2026 15:20:33 +0000

You want to remove a handful of chunks, but MCA Selector will only let you select — and delete — entire regions at once. This is reported upstream as issue #529 (“Unable to delete individual chunks, only whole regions”), and it is not a bug in your install: it is the tool’s zoom-dependent selection modes doing exactly what they are designed to do.

Why it happens: two selection modes, one zoom control

MCA Selector’s map has two selection granularities. Zoomed out, you are in region mode: each cell of the grid is a whole region file — 32×32 chunks, 512×512 blocks. Zoomed in far enough for the chunk grid to appear, the same clicking selects individual chunks. If the view is zoomed out, single-chunk selection simply is not available, which is why every selection snaps to whole regions.

Fix it step by step

Open your world and find the area you want to edit.
Zoom in (mouse wheel) until you can see the fine grid of individual chunks — the selection highlight will now follow single chunks instead of region-sized blocks.
Click or drag to select exactly the chunks you intend to delete.
Before deleting, read the selection back: zoom and pan to confirm the highlight covers only what you meant to remove.
Delete via Selection → Delete selected chunks — and remember it is instant and irreversible.

The selection modes, including brush selection with Shift and subtraction mode, are covered in full in our selection tools guide, and the deletion workflow itself in how to delete chunks.

Already deleted a whole region by accident?

This is the scenario in issue #447, and we will not sugar-coat it: there is no undo. Deletions modify the original region files the moment you confirm, and the tool keeps no recycle bin or backup of its own. The only recovery path is restoring the world (or the affected region files) from a backup you made before editing. If you have no backup, the deleted terrain will regenerate as fresh chunks the next time Minecraft loads that area — anything built there is, unfortunately, gone.

Prevention checklist

Back up the whole world folder before every editing session — with instant writes, this is your only undo.
Check whether you are in chunk mode or region mode (zoom level) before selecting.
For valuable selections you may need again, export the selection as a CSV first (Selection → Export selection).
Re-read the highlighted area once more before confirming a delete — especially near the borders of regions you want to keep.
Work on a copy of the world for destructive experiments, then repeat the confirmed steps on the real one.

If zooming in does not switch modes

Issue #529 is still open upstream, so if the chunk grid appears but selection still snaps to regions on the current version (2.9), note your zoom level, MCA Selector version and operating system and add them to that issue — precise reproduction details are what an open report like this needs.

Get the Current Version First

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This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector Changes Not Saving? How Saving Actually Works

Admin — Wed, 21 Oct 2026 15:20:15 +0000

“I deleted a bunch of chunks, closed MCA Selector, and nothing changed — did it not save?” Or the opposite worry: “where is the save button?” Both questions come from the same misunderstanding, and the answer surprises most people: MCA Selector has no save step at all. Understanding how it actually writes changes explains almost every “changes not saving” report.

How saving actually works in MCA Selector

Deletions are written the moment you confirm them. Selection → Delete selected chunks and filter-based deletes modify the original region files immediately. The official wiki is blunt about it: “This operation is instant and there is no going back.”
NBT Changer edits are also instant. When you run a change, it is applied to the files on disk — there is no document to save afterwards.
The one exception is the Chunk Editor. Editing a single chunk’s NBT tree (Ctrl+B) is staged: nothing is written until you press Apply. Close the editor without Apply and the edit is discarded by design. See our Chunk Editor guide for that workflow.
Selections are not saved with the world either. If you want to keep a selection itself, export it as a CSV (Selection → Export selection) and import it later — that is the tool’s equivalent of “saving your work area”, as covered in our selection tools guide.

So why did your change “not take”?

You edited a different folder than you think. The classic case: you opened a backup copy (or a copy you made “just to test”), edited that, then loaded the original in Minecraft. Check the path in File → Open World against the world folder Minecraft actually loads.
The world was open in Minecraft or on a server while you edited. MCA Selector is an external tool; the game holds its own copy of the world in memory and can overwrite your edits when it saves or shuts down. Always close the world (and stop the server) before editing.
You closed the Chunk Editor without pressing Apply — see above; that is the one place a “forgot to save” really can happen.
The change has no visible effect by design. Some NBT Changer fields only matter under specific conditions — ForceBlend, for example, only affects blending between chunks generated by Minecraft 1.18 and its neighbours, so on older terrain it visibly does nothing even though it ran (issues #568/#552 track this confusion upstream).

A safe editing routine

Close Minecraft completely, and stop your server if the world lives on one.
Copy the entire world folder somewhere safe — because writes are instant, this copy is your only undo.
Open that original folder in MCA Selector and double-check the path before changing anything.
Make your edits. For deletions and NBT Changer, consider them live the second you confirm.
In the Chunk Editor, press Apply before closing.
Reopen the world in Minecraft and verify, keeping the backup until you are sure.

Our complete beginner’s guide walks through this routine in context, and the NBT Changer guide covers which fields write what.

If changes genuinely vanish

Work through the four causes above in order — wrong folder and a still-running game or server account for nearly all of them. If the path is right, the game was closed, and an instant operation (a deletion) still leaves the chunk in place when you reload the world in MCA Selector itself, note the exact steps and versions and check the official issue tracker; that combination is unusual enough to be worth reporting.

Get the Current Version First

More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector Not Opening: Diagnose a Silent Launch or Blank Window

Admin — Wed, 21 Oct 2026 15:19:56 +0000

You double-click MCA Selector — the .exe or the .jar — and nothing happens. No window, no error. Or a window opens but stays blank. These silent failures are reported upstream in issues #608, #534 and #262, and they are frustrating precisely because there is no message to search for. The way out is to make the error visible.

Step 1: launch from the command line and read the error

A double-click hides Java’s error output; a terminal shows it. Open a terminal (Command Prompt or PowerShell on Windows, Terminal on Mac/Linux), go to the folder with the .jar, and run:

java -jar mcaselector-2.9.jar

Now read what it prints. In practice it will name one of the causes below — and if it prints nothing and the window appears, your installation is fine and the problem was the double-click association.

Cause A: your Java is too old

The current MCA Selector requires Java 21 or newer. In issue #608, the reporter’s Java turned out to be version 1.8 — years too old — and the tool simply died on launch. Errors mentioning UnsupportedClassVersionError or NoClassDefFoundError: javafx/scene/paint/Color mean the same thing. Run java -version to check, then fix your runtime as described in our Java requirements guide. On Windows, the easiest route is the official installer, which since 2.8 bundles its own runtime and needs no Java at all.

Cause B: JavaFX is missing

If the terminal output mentions JavaFX or its modules, your Java 21+ runtime lacks the JavaFX toolkit. That has its own dedicated fix — a JavaFX-bundled JRE or the module-path launch command — in our Missing JavaFX guide.

Cause C: the window opens but the map is blank

If the program starts but no terrain renders, suspect the render cache before anything else: the tool caches rendered region images, and a stale or corrupt cache can leave you staring at an empty view. The official wiki’s remedy is to clear the cache so every region re-renders from the world files. Restart the tool afterwards and give large worlds a moment — the first render has real work to do.

If it still does not work

Collect the three facts that make this diagnosable — your operating system, the output of java -version, and the exact terminal output from Step 1 — and search the Querz/mcaselector issue tracker for your error text before opening a new issue; #608, #534 and #262 are still open, and adding your terminal output to the matching one is more useful than a “me too”. Do not download “fixed” builds from third-party sites: the only official source is the GitHub release, linked from our download page.

Get the Current Version First

More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector Missing JavaFX: How to Fix the Launch Error

Admin — Wed, 21 Oct 2026 15:19:36 +0000

You double-click the MCA Selector .jar and, instead of the map view, a dialog complains that JavaFX is missing — variants of the message include “Fails to find JavaFX” and errors naming javafx/scene/paint/Color. This is tracked upstream in issues #379 and #518, and it has nothing to do with your world: it is purely about the Java runtime you launched the .jar with.

Why it happens

MCA Selector’s interface is built with JavaFX, but JavaFX is not part of a standard Java installation. The current release needs a 64-bit JRE 21 or newer that includes JavaFX — either pre-packed or installed separately, as the official installation guide puts it. Most people’s Java (the one bundled with Minecraft, or a plain OpenJDK download) does not include JavaFX, so the .jar starts, cannot find the toolkit, and stops. The full background is in our guide to MCA Selector’s Java requirements.

Fix 1: use a Java runtime with JavaFX built in (easiest)

Download a JRE 21 (or newer) with JavaFX pre-packed — the official guide’s example is Azul Zulu JRE-FX 21. Make sure you pick the 64-bit FX edition, not the plain JRE.
Install it, and make sure it is the Java your system uses for .jar files (on Windows, right-click the .jar → Open with → choose the new runtime; or launch from a terminal as in Fix 2).
Start MCA Selector again. The JavaFX dialog should be gone.

Fix 2: add the JavaFX SDK yourself

If you prefer to keep your existing Java 21+ runtime, download the JavaFX SDK separately and tell Java where it is when launching, exactly as the official installation guide describes:

java --module-path /lib --add-modules ALL-MODULE-PATH -jar mcaselector-2.9.jar

Replace with the folder you extracted the JavaFX SDK into.
On Linux, your distribution’s openjfx package provides the same modules — install it via your package manager, or use the native packages in our Linux install guide.

Or skip Java entirely on Windows

Since version 2.8, the Windows installer (mcaselector-2.9-setup.exe) pre-packages its own runtime, so .exe users do not need to install Java or JavaFX at all. If the .jar route keeps fighting you on Windows, switching to the installer from the download page is the simplest permanent fix.

If it still does not work

Issues #379 and #518 are still open upstream, but almost every case resolves to the runtime: run java -version in a terminal and confirm it reports 21 or newer and is the same Java that launches the .jar — having Java 21 installed does not help if the .jar is still associated with an older runtime. If the version and the JavaFX modules are both right and it still fails, report it on the issue with your exact error text and launch command.

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More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.

MCA Selector ‘No Dimensions Found’ Error: Causes and Fixes

Admin — Wed, 21 Oct 2026 15:18:32 +0000

You open MCA Selector, choose File → Open World, pick your world — and instead of a map you get an error saying “No Dimensions found”. The world is fine in Minecraft, so what is the tool complaining about? This is one of the most reported issues on the project’s GitHub tracker (issue #295), and in most cases the cause is simply the folder you selected.

What the error actually means

MCA Selector does not open a world by its name — it reads the folder you give it and looks for dimension data inside it. A Minecraft Java Edition world keeps that data in sub-folders called region and poi (plus entities on newer versions), which sit directly inside the world’s own folder, next to level.dat. If the folder you select does not directly contain a region or poi sub-folder, the tool concludes there are no dimensions to show — because from its point of view, there aren’t.

The usual causes

You selected one level too high — for example the saves folder itself, or your whole .minecraft folder, instead of the individual world folder inside saves.
You selected one level too low — for example the region folder itself. The tool wants the folder that contains region, not region itself.
The save is a Bedrock Edition world. Bedrock stores its world in a LevelDB database, not in .mca region files, so MCA Selector finds no Java dimensions in it. The maintainer has stated there are no plans to support the Bedrock format — see our guide on MCA Selector and Bedrock for what to use instead.
A known open bug. Some users have reproduced the error on valid Java worlds (including a 1.21.1 save) even with the right folder selected. Issue #295 is still open upstream, so if the folder checks below all pass, you may be hitting the bug itself rather than a mistake.

Fix it step by step

Close the error and go to File → Open World again.
Navigate into your saves folder and then into the world’s own folder — the one whose name matches the world as it appears in Minecraft’s single-player list.
Before confirming, check the folder’s contents in your file manager: you should see level.dat and sub-folders named region and poi right there. If you see a list of other world folders instead, you are one level too high; if you see only .mca files, you are one level too low (inside region).
Select that folder. The map should now render.
If the folder is correct and it still fails, update MCA Selector to the current version (2.9) and try again — world-format support moves with each release, and older builds can fail on newer saves.
As a sanity check, try opening a different, freshly created Java world. If that one loads, the problem is specific to the first save; if nothing loads, the problem is the installation, not the world.

If it still does not work

Issue #295 remains open on the official tracker at the time of writing, so there is no guaranteed upstream fix yet — the steps above are the workarounds that help most users. If your folder is definitely the world root and you are on the current version, the most useful next step is to add your details (Minecraft version of the world, MCA Selector version, operating system) to that issue on the Querz/mcaselector GitHub repository, since reproducible cases are what moves an open bug forward.

Get the Current Version First

More troubleshooting

This page is part of our MCA Selector troubleshooting hub, which groups every known launch, loading and editing problem by symptom.