ModSync

Join a modded server without hunting down a single mod. It syncs them for you.

by Duzo

What is it?

A Minecraft Forge mod that lets clients automatically download the mods a server is missing - so joining a modded server is one click instead of a manual mod hunt. Think "gmod addon share", but for Minecraft.

Features

• 🔄 Automatic mod detection - a "Sync Mods" button appears on the mod-mismatch disconnect screen.
• 🔒 SHA-256 verification - downloaded mods are checked against the server's checksums.
• 🔁 Auto-reconnect - rejoins the server after the restart.
• 🌐 IPv4 & IPv6 - works with all server address formats.
• ✅ User consent - always asks before downloading anything.

How it works

Server side - running the mod starts a small HTTP server (default port 25566, configurable) that serves the installed mod list with SHA-256 checksums and lets clients download the JARs.

Client side

1. Try to connect to a modded server.
2. If you're kicked for a mod mismatch, click Sync Mods.
3. Review the missing mods and confirm the download.
4. Mods drop into your mods folder.
5. Click Restart Now - the game reconnects automatically.

Required on both the server and the client.

Configuration

config/modsync-common.toml:

[server]
httpPort = 25566      # HTTP port for serving mod files
serverSecret = ""     # shared secret for downloads (empty = no auth)

[client]
autoDownload = false  # start downloading missing mods automatically (still asks consent)
autoRestart = false   # restart automatically after download

⚠️ Security

Only sync mods from servers you trust. Mods have full access to your computer - ModSync verifies file integrity, but it can't vouch for what a mod actually does.

Requirements

• Minecraft 1.20.1
• Forge 47.4+

Building

git clone https://github.com/duzos/modsync.git
cd modsync
./gradlew build      # output in build/libs/

Links

• Releases
• GitHub

License

MIT. Issues and PRs welcome.