The Windows Helper: real Java worlds on your PC

A browser on its own cannot run a Java server. The Helper can: it is a small Windows program that starts genuine servers on your own machine, and the site connects to them. You install it once and never open it again.

What it actually does

When you choose to create a real Java world, the page does not simulate anything: it asks the Helper to start an actual server (vanilla or Paper) on your PC, and then connects to it. The world that comes out of it is a standard Java world, with its own generation, its own mechanics and ordinary save files.

The Helper has no window, no taskbar icon, nothing to open. It lives in the background, starts by itself when you turn the PC on, and the site finds it on its own.

Before installing: Java

You need Java 17 or later on the machine. If you do not have it, the usual choice is the LTS installer from adoptium.net, which is next-next-finish. To check whether you already have it, open the Start menu, type cmd, and in the black window type java -version.

Installing, just the once

1. Download the ZIP from the real Java server section inside the game itself.
2. Actually extract it, with right-click and “Extract All…”. This matters: running the installer from the ZIP preview will not work, because it needs the files that come with it.
3. Clear the warning first (recommended, 10 seconds): right-click Instalar.cmd → Properties → at the very bottom tick “Unblock” → OK. That is the one thing that stops the blue screen from ever appearing. If you cannot see the checkbox, Windows did not add the mark and you can carry on.
4. Open Instalar.cmd as administrator: right-click → “Run as administrator”. That way it starts with permissions and will not interrupt you halfway through. A plain double-click works too: the installer asks for them by itself.
5. If the administrator prompt (UAC) appears, accept it. And if you cancel it, or your account is not an administrator, no harm done: the installation carries on in user mode and works just the same, because nothing it does needs administrator rights.
6. When it finishes, the site opens by itself. That is all: do not run the installer again.

The SmartScreen warning

If you did not tick the “Unblock” box in the step above, the first time round Windows will show a blue screen saying “Windows protected your PC”. You have to click “More info” and then “Run anyway”.

It is worth explaining why it turns up, because it is scarier than it deserves to be. SmartScreen warns about any program that is not signed with a paid digital certificate, and those certificates cost money every year. The warning does not say the program is dangerous: it says Windows does not recognize who signed it, which is not the same thing.

Two things people usually ask. First: running it as administrator does not avoid this warning by itself, because Windows shows it before the program even starts — what does avoid it is the “Unblock” box in the file's properties, or clicking “Run anyway”. Second: it only appears this one time. The installer strips the “mark of the web” that Windows puts on everything downloaded from the extracted files, and after that the warning does not come back.

Where everything ends up

It all hangs off your user folder. The quick way there is to paste %LOCALAPPDATA%\Webcraft into the File Explorer address bar.

• Worlds: %LOCALAPPDATA%\Webcraft\mundos-java
• Program: %LOCALAPPDATA%\Webcraft\asistente
• Activity log: %LOCALAPPDATA%\Webcraft\asistente\logs\helper.log

Keeping the worlds outside the program folder is deliberate: uninstalling or reinstalling the Helper does not take them with it. Since they are ordinary server folders, you can copy them for a backup, or move them somewhere else.

How you use it

You do not. That is the whole idea. You go to the site, choose the real Java server and create your world; the page talks to the Helper by itself. The Helper answers requests on port 8080 on your machine, and during installation a Windows Firewall rule is added for that port, so people on your local network can play too.

The Helper does not update itself and does not download code on its own. When there is a new version, the site will tell you and you will download the ZIP by hand.

If something goes wrong

• It is normally already running, but you can start it by hand from Start menu → Webcraft → “Asistente Webcraft (arrancar)”.
• The end of helper.log says exactly what failed. It is the first place to look.
• If it will not start, the usual cause is another program already using port 8080.
• Check that Java is still installed with java -version.

Uninstalling

From Start menu → Webcraft → “Desinstalar Asistente Webcraft”, or by running Desinstalar.cmd from the program folder. The uninstaller will ask whether you want to keep your worlds: say yes and the program goes while your saves stay exactly where they are.