Mismatched mod channel list: what it means and how to fix it

You start your modpack, click the server, and get bounced back to the menu. On Forge the message says Connection closed - mismatched mod channel list; on NeoForge 1.21.1 you get a screen headed "Your client is missing the following mods", "The server is missing the following mods" or "The following mod versions do not match". The game is fine. The server is fine. They just don't agree with each other.

What the message means

Modded Minecraft servers check, when you join, that your game has the same mods as the server. Each mod that talks between client and server opens a "channel", and the server compares its list of channels with yours. If one side has a mod the other doesn't, or a different version of it, the lists don't match and you're turned away.

So "mismatched mod channel list" means one thing: your mods are not the server's mods.

The common causes

• Different pack versions. The server updated the pack and you didn't, or the other way round. This is the most common cause by far.
• A mod you added yourself. You installed an extra mod that adds items or blocks. Purely visual mods are usually fine; anything that adds content has to be on the server too.
• A mod the server dropped. Someone removed a mod from the server to fix a crash and forgot to tell everyone.
• Different versions of the same mod. The launcher auto-updated a mod on your side.
• Config differences (rare). A few mods check their own settings when you join. NeoForge sends server settings to players itself, so this is seldom the cause.

How to fix it

1. Read the full message

NeoForge 1.21.1 lists the mods on the disconnect screen, in a table of channel names with what you have and what the server has. If the list is cut short ("see latest.log for the full list"), open logs/latest.log in your game folder and read the lines around the disconnect. That list is your to-do list.

2. Match the pack version

Check which version of the pack the server runs, and install exactly that one. If you made the pack yourself, compare your mods folder with the server's, name by name and version by version.

3. Remove your extras

Temporarily take out any mods you added on top of the pack. If you can join without them, add them back one at a time to find the one that needs to be on the server too.

4. Try the server's config folder

Rarely, a mod checks its own settings on join. If the mod lists match and you still can't connect, copy the server's config folder to your game (back up your own first).

5. Turn off auto-updates

Once everyone can connect, turn off automatic mod updates in your launcher for this pack, so it doesn't happen again next week.

The other direction: the server won't start

The reverse problem is a server that crashes while starting because it has a mod meant only for players: a minimap, a shader loader, a menu tweak. Those are client-only mods. They must stay in players' games and out of the server's mods folder. Mod pages usually say whether a mod is needed on the client, the server or both, though not always correctly. Our guide to making a modded Minecraft server covers setting one up from scratch.

How Packspire avoids it

On every paid plan, Packspire makes the player pack and the server pack from one mod list, so they can't drift apart. During the build, a real game client joins a server running the pack and stays in the world for a minute. If the server turns it away, the reason goes in the build report, so it can be fixed before anyone downloads the pack.

Build a pack you can play with friends, or read our guide to making a modpack your friends will actually play.

Frequently asked questions

What does mismatched mod channel list mean?

A modded server compares its mods' network channels with your game's when you join. If one side has a mod or mod version the other doesn't, the lists differ and the server disconnects you. The exact phrase is Forge's; NeoForge 1.21.1 shows the same problem as a table of missing or mismatched mods.

Can I join a modded server with extra client mods?

Often yes, for purely visual or client-only mods like minimaps or shaders. Any mod that adds blocks, items or mobs must be on both sides.

Why does my server crash with a client-only mod?

Client-only mods use parts of the game that don't exist on a dedicated server, such as rendering. Remove them from the server's mods folder and keep them in players' games.

Do configs have to match between client and server?

Rarely. NeoForge sends server settings to players itself, but a few mods check their own settings on join. If the mod lists match and you still can't connect, copying the server's config folder is worth a try.

Sources

• NeoForge networking docs (1.21.1), on how mods' channels are checked when you join
• NeoForge 1.21.1's English text, for the exact wording of the mismatch screen