Direct answer

Broad mismatch vs. specific handshake error

Use this broad guide when the loader/client reports that mods differ. The channel-list and registry guides cover more specific handshake stages and should be used when those exact messages appear.

Use the same Minecraft version, compatible loader version, and the mod/modpack versions required by the server. For a modpack, the safest baseline is usually to install the exact same pack release on the client and the matching server pack on the server.

Compare more than the Minecraft number

  • Minecraft version
  • Fabric/Forge/NeoForge loader version
  • Modpack release/version
  • Required mod IDs and their versions
  • Required dependencies/libraries
  • Server-side configuration or datapack files when the pack documentation requires them

Not every client mod belongs on the server

Visual/UI/client-only mods may be intentionally absent from a dedicated server. Fabric metadata can explicitly mark a mod as client, while NeoForge’s server guide notes that server packs often remove client-side mods for you. Do not “synchronize” by blindly copying every client JAR onto the server.

Use the server pack when available

NeoForge recommends using a modpack’s server pack when it exists. Server packs are prepared for dedicated-server use and reduce the chance of shipping client-only files or omitting server-specific configuration.

After an update

Update the server and clients together. If only the client auto-updated to a newer pack release, either roll that client back to the server’s release or update the server after a backup and compatibility check.

Compare exact identities, not mod counts
  1. Compare mod IDs, loaders and dependency versions in both server and client logs. Two packs with the same number of JAR files can still be incompatible.
  2. Check whether each mod is client-only, server-only or required on both sides; do not copy client-only rendering mods into a dedicated server automatically.
  3. Use the modpack author’s server pack and its lockfile/manifest where provided, then add back optional changes one at a time.

Official references

These references were checked while preparing this fix. Version-specific behavior can change, so use the project documentation for your exact release when a detail differs.

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