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