Minecraft Server Builder

Java is missing, or I do not know what Java is

A Minecraft server is a Java program, so your computer needs Java installed. The start file checks this for you and tells you which version you need.

To see what you have: open Command Prompt (Windows) or Terminal (Mac and Linux), type java -version and press Enter. A line like openjdk version "25.0.5" means Java is installed, and the number after the quote is its version. An error means Java is not installed.

1. Open the Adoptium download page. It is a free, trusted build of Java.

2. Choose your operating system and the Java version number from the table below. Pick the JDK and the installer file (.msi on Windows, .pkg on Mac).

3. Run the installer. If it offers to add Java to the PATH, keep that option selected.

4. Close your Command Prompt or Terminal window, open a new one, and type java -version again. Then run the start file again.

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On Linux your package manager may offer these Java versions; otherwise download the archive from the same page.

It still says Java is missing? Close the window and open a new one: Java is found when a window opens. If that fails, restart the computer. If java -version shows an older number than the table asks for, install the newer Java and open a new window.

The window closes straight away

The start file waits for a key press before it closes, so you can read the message. If the window still disappears, open Command Prompt, go to the server folder (type cd and a space, drag the folder into the window, press Enter) and run start.bat. Whatever it prints is the reason.

The usual reasons are on this page: Java is missing, the download did not finish, or the port is already in use.

Windows or macOS warns about the start file

Windows may say Windows protected your PC. The start file is a plain text file: open it in Notepad to read exactly what it does. If you are happy with it, choose More info, then Run anyway.

Mac: open Terminal in the server folder and type sh start.sh. This runs the text file through the terminal, which normally avoids the "unidentified developer" warning.

The download stopped, or the checksum did not match

Run the start file again: it carries on where it stopped. The server file comes from Mojang's own download address and the script checks it against Mojang's checksum, so a damaged or changed file is thrown away instead of used.

If it keeps failing, check your internet, turn off a VPN, and check that a school or work network, or an antivirus, is not blocking piston-data.mojang.com and launcher.mojang.com.

My friends cannot join

localhost only works on the computer that runs the server. Friends need a different address.

Friends on the same Wi-Fi or home network: they need your computer's local address. On Windows open Command Prompt, type ipconfig and look for "IPv4 Address" (it looks like 192.168.1.23). On Mac or Linux look in the network settings. Friends type that address in Add Server.

Friends on the internet: your router has to pass incoming connections to your computer. This is called port forwarding: in your router's settings, forward TCP port 25565 (or the port you chose) to your computer's local address. Friends then use your public IP address. Some internet providers do not allow this. Only share the address with people you trust.

Everyone must also use the same Minecraft version as the server.

The port is already in use

Another program, often another Minecraft server still running in a hidden window, is using the same port. Close it, or choose a different port in the Advanced step and download again.

Friends then add the new port after the address, like 192.168.1.23:25570.

Players see "outdated client" or cannot connect

The Minecraft game must be the same version as the server. In the Minecraft Launcher choose an installation for exactly that version: open Installations, choose New installation and pick the version.

The version of your server is shown in the summary on the last step, and in the first lines of the server window.

Where is my world, and how do I stop the server safely?

Your world is saved in a folder called world inside the server folder.

To stop the server, type stop in the server window and press Enter, then wait until it closes. This saves everything. Closing the window, or switching the computer off, without doing this can lose recent progress.

To make a backup, stop the server and copy the world folder somewhere safe.

The server is slow or uses too much memory

Try these in order: close other programs; lower View distance and Simulation distance in the Advanced step (10 is the default, 6 is much lighter); give the server a little more memory in the Basics step, but never more than your computer has free; make sure the computer is plugged in and not in power-saving mode.

Why are PvP and command blocks crossed out?

From Minecraft 1.21.9 these two settings moved from the server settings file into the game itself, so this page cannot change them. As an operator you can change them in the game with the /gamerule command.

If you need this page to set them, pick version 1.21.8 or older.

How do the allow list and the block list work?

The allow list means only the names you list, and you, can join. The block list keeps named players out for good, and a blocked address keeps a computer out.

The first time you start the server, the start file looks each name up with Mojang (it needs the internet for a moment) and writes whitelist.json, banned-players.json and banned-ips.json. A name it cannot find is printed in the window, and the server still starts.

If the allow list is on and no name could be looked up, the start file stops instead of starting a server nobody can join. Check your internet and run it again.

Files you already have are never overwritten. To change a list later, type in the server window: whitelist add NAME, whitelist remove NAME, ban NAME, pardon NAME, ban-ip ADDRESS or pardon-ip ADDRESS.

How do I use my own map?

In the Gameplay step, choose your map folder (or a .zip of it). The page reads only one small file, level.dat, on your computer. Nothing is uploaded.

1. Download your zip as usual and unzip it.

2. Copy your map folder (the one with level.dat inside) into the new server folder, next to start.bat.

3. Run the start file. The server opens your map instead of making a new world.

A map saved by a newer Minecraft than the server cannot be opened: choose that version or newer. An older map is upgraded the first time, and that cannot be undone, so keep a copy. Bedrock Edition maps do not work. Resource packs are not supported yet.

What does the settings editor do, and is it safe?

The last question on the Advanced step shows the whole server.properties file for your version. Edit any line, or drop your old file onto the box to import it.

Only the lines you change are kept. Change an answer on another page and the file follows, except for the lines you edited yourself. Delete a line to put it back to normal.

Lines this version does not have, or values of the wrong kind (text where a number is needed), are marked and must be fixed before you can download. A few settings show a “Careful” warning, for example online-mode=false, which lets anyone join under any name.

Passwords (like rcon.password) stay in your download but are never put in the share link or saved in your browser.

What is the EULA?

The EULA is Mojang's license for running Minecraft servers. Minecraft refuses to start a server until someone agrees to it.

This page only writes eula=true into your download if you tick the box yourself. Read it first at aka.ms/MinecraftEULA. You can change your mind later by deleting eula.txt or setting it to false.