Minecraft server won't start: how to find the cause and fix it

Open the panel and look at the badge next to the server name. Offline with a Start button means the server stopped; click Start once and switch to the Console tab while it boots.

1. In the Console tab, set the level filter to Errors. Only the red lines stay.
2. Look at the first error, not the last. The last lines are often a result of the first one.
3. Still unclear? Set the filter to Warnings as well; a warning just before the error often names the plugin or file.
4. Type a word from the error, such as a plugin name, in the search box above the log to see every line about it.

Did the server stop before you opened the console? The full log of the last start is saved in the Files tab, in logs/latest.log. Older starts are kept next to it as .log.gz files, which the panel can extract for you.

Your error is not in the table? Copy the first red line into a search engine together with the word Minecraft. Almost every startup error has been hit by someone before, and the top result usually names the fix.

When the log names a plugin, you do not have to delete it. Rename the file so the server skips it, start the server, and decide later what to do with it.

1. In the Files tab, open the plugins folder.
2. Click Rename on the plugin's .jar file and add .off to the end, for example BrokenPlugin.jar.off.
3. Start the server. It ignores every file that does not end in .jar.
4. Once you have a version that fits, upload it and delete the .off file.

No plugin named in the log, but the problem began after you added several at once? Turn off half of them, start, and repeat with the half that still fails. On a modded server the same trick works in the mods folder.

Before you change anything else, make a backup in the Backups tab. If a fix makes it worse, you can go straight back. Back up and restore your server shows how.

A single wrong character in a config file can stop the server at boot. The log then names the file, often with a line number.

1. Open the file in the Files tab with Edit. For the main settings that is server.properties in the top folder.
2. Go to the line from the error. In .yml files, look for a tab instead of spaces, or a missing space after a colon.
3. Save and start the server again.

Anything that is also offered in Settings, such as the server type or the Minecraft version, is safer to change there. The panel then writes the file for you, without a typo.

After a change of Minecraft version, plugins and mods can stop fitting, and an old world can need a newer Java. Settings shows both in one place.

• Under Startup, the Java version shows which Java is recommended for your Minecraft version. A newer Java than needed is almost always fine; an older one will not start the server.
• Changing the Minecraft version sets the matching Java again by itself.
• Both take effect at the next restart, so start the server after saving.

Which Java version your server needs has the full list per Minecraft version.

A server that stopped during a save, or a world uploaded half, can leave a region or level.dat file damaged. The log then mentions reading one of those files. The quickest safe fix is your latest backup: stop the server, restore it in Backups, and start again.

No backup? Download the world folder first, so nothing gets lost. Then send us a message from the client area with the error line; we look at it with you.

Sometimes there is no clear error: the server stays on one line for minutes, or stops itself with a long block of text. These messages explain what happened.

Modded servers fail at startup more often than plugin servers, because every mod has to fit the loader, the Minecraft version and the other mods. The usual messages:

• `Incompatible mods found!` on Fabric, or `Missing or unsupported mandatory dependencies` on Forge and NeoForge: a mod needs another mod, or another version of it. The lines below name both.
• `is not a valid mod file`: the file is made for another loader, such as a Fabric mod in the mods folder of a Forge server.
• A class under `net/minecraft/client` in the error: a mod that only belongs in the players' game is on the server.
• `Crash report saved to`: open that file in the crash-reports folder. Its description says what failed, and Forge and NeoForge add the mods they suspect.

Install mods on a Minecraft server has a table of these errors with the fix for each one.

A version change is the moment most servers stop starting, for two reasons.

• Plugins or mods that do not support the new version yet. Turn them off with the .jar.off trick and add them back as updates come out.
• A world that was opened in a newer version. Paper refuses with Server attempted to load chunk saved with newer version of minecraft. Worlds cannot go back to an older version; set the newer version again, or restore the backup from before the change.

Switching versions safely goes backup first, then plugins, then the switch itself; change your Minecraft server version walks through it.

Still stuck? Download logs/latest.log and, if there is one, the newest file in crash-reports, and send them with a short note of what changed last. We answer every day between 07:00 and 23:00 CET, and with the log in hand we can usually point at the line straight away.