Direct answer

First install the correct mod-loader server distribution, then place compatible server mod JARs in its mods/ folder. A Paper/Spigot plugins/ installation is not interchangeable with this process.

Recommended procedure

  1. Back up the world. Choose the exact Minecraft version and mod loader required by your mods or modpack. Install and start that loader’s dedicated server using the official installer or server pack.
  2. Stop the server. Locate the server directory used by the startup script and create or open its mods/ folder.
  3. Download the mod versions that explicitly support the loader and Minecraft release; also install any required library mods such as a compatible Fabric API version if specified.
  4. Copy server-compatible JARs into mods/. Do not blindly copy shaders or other client-only libraries to the dedicated server.
  5. Start the server; read console errors and logs/latest.log or loader-specific log output. Resolve wrong loader, missing dependency and unsupported Java/runtime errors before letting players join.

Why this matters

A working Java Edition vanilla server is not automatically a modded server. Fabric, Forge and NeoForge each use their own loader installation process and mod dependency ecosystem.

How to verify the result

  • Inspect the startup log and loader mod list for successful loading.
  • Join using a compatible client installation; verify a modded feature works and no registry mismatch occurs.
  • If changing existing world content, test on a copy first and retain the pre-installation backup.

Version and compatibility notes

Important

File locations and launch commands vary by loader and host. Follow the exact loader installer or modpack server-pack documentation for your release instead of copying generic start scripts.

Official references

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