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Common Minecraft Launcher Errors

Find solutions to the most frequent issues encountered with Minecraft launchers. Can't find your answer? Contact us.

1. The launcher won't start

Symptoms: The launcher doesn't open, opens then closes immediately, or shows a blank screen on startup.

Solutions:

  1. 1 Check that Java is installed (version 17 or higher for recent Minecraft versions). CraftLauncher manages the Java runtime automatically, but if you use an external launcher, make sure you have the right version.
  2. 2 Temporarily disable your antivirus or add the launcher as an exception. Some antivirus software (Windows Defender, Avast, Kaspersky) blocks unsigned executables.
  3. 3 Run the launcher as administrator (right-click > Run as administrator). On Linux, check that the .AppImage file has execute permissions (chmod +x).

2. Incompatible mods

Symptoms: The game crashes while loading with an error message mentioning a mod conflict, or the game launches but some mods don't work.

Solutions:

  1. 1 Check that all your mods use the same mod loader. A Forge mod does NOT work with Fabric and vice versa. See our Forge Launcher or Fabric Launcher page for more details.
  2. 2 Make sure all your mods are compatible with your Minecraft version. A mod for 1.20 won't work on 1.21 without a developer update.
  3. 3 Remove mods one by one to identify the one causing the issue. Start with the most recently added mods.

3. Crash on game startup

Symptoms: The game launches but crashes immediately after the loading screen, with a crash screen or an error report.

Solutions:

  1. 1 Increase the memory allocated to the game. In the launcher settings, set RAM to 4 GB minimum for modpacks, and 6-8 GB for large modpacks. Avoid exceeding 12 GB (it can cause lag spikes).
  2. 2 Delete the corrupted config folder: go to the launcher's installation directory, then delete the /config folder. The game will recreate it automatically on the next launch.
  3. 3 Check that your GPU is up to date. Update the graphics drivers (NVIDIA, AMD, Intel) from the manufacturer's official website.

4. Unable to connect to the server

Symptoms: The message "Unable to connect to the server" or "Connection refused" appears when you try to join.

Solutions:

  1. 1 Check that the game version matches the server's exactly. A 1.20.4 client cannot connect to a 1.20.6 server.
  2. 2 Temporarily disable your firewall (Windows Firewall) or add an exception for the server port (default 25565). Corporate or university networks often block Minecraft ports.
  3. 3 Check the server's IP address and port in the launcher configuration. If you're using a domain name, try the IP address directly.

5. Mods aren't loading

Symptoms: The game launches but the mods aren't present, mod blocks/items don't appear in the game.

Solutions:

  1. 1 Check that the correct mod loader is installed. CraftLauncher configures Forge or Fabric automatically based on your modpack, but if you manually modified files, the loader may be missing.
  2. 2 Check for missing dependencies. Some mods require extra libraries (Fabric API, Forge API, Cloth Config, etc.). The launch log shows which dependencies are missing.
  3. 3 Delete the /mods folder and relaunch the launcher so it re-downloads the mods from the CDN. Corrupted files prevent loading.

6. The launcher is slow

Symptoms: The launcher takes a long time to open, the dashboard pages are slow, or mod downloads take very long.

Solutions:

  1. 1 Check your internet connection. The launcher downloads mods and updates on first launch. On a slow connection, this can take several minutes. Subsequent launches will be faster thanks to caching.
  2. 2 Adjust the JVM arguments in the launcher settings. Use -XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 for better performance.
  3. 3 Close background applications that consume RAM and CPU (browser with 50 tabs, streaming software, etc.). Minecraft with mods requires at least 4 GB of free RAM.

7. Download error

Symptoms: The launcher shows an error during mod download, a file won't download, or the download stops midway.

Solutions:

  1. 1 Check your internet connection and try again. Temporary interruptions (switching WiFi, 4G drop) stop downloads. The launcher will resume where it left off.
  2. 2 If you use a VPN or proxy, temporarily disable it. Some services block downloads from CDNs.
  3. 3 Check that your firewall or antivirus isn't blocking outbound connections to Cloudflare servers (R2). CraftLauncher uses Cloudflare R2 to distribute files. In a corporate environment, contact your network administrator.

8. Microsoft authentication issue

Symptoms: The message "Authentication failed" appears, the Microsoft login window doesn't open, or you're regularly logged out.

Solutions:

  1. 1 Check that your Microsoft/Mojang account is active and that you actually own Minecraft Java Edition. Xbox Game Pass accounts require an active subscription.
  2. 2 Clear the launcher cache: go to settings and click "Clear cache" or manually delete the /cache folder in the installation directory.
  3. 3 If the Microsoft login window doesn't open, check that your default browser is configured correctly. Try temporarily switching your default browser (Chrome, Firefox, Edge).

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