Bad Packets — A Mod for Cross-Modloader Packet Exchange in Minecraft

Bad Packets — A Mod for Cross-Modloader Packet Exchange in Minecraft

Bad Packets is a library mod for Minecraft that lets other mods send custom network packets between the client and the server even when the client and server run on different modloaders. On its own, this mod adds no new content for players, but it's a required dependency for a whole range of other popular mods that rely on it.

What Bad Packets Does

Inside Minecraft, the client and server constantly exchange service messages — packets. Any mod can create its own packet types, for example to send extra block data or information from the server to the client that isn't part of the vanilla protocol. The problem is that Fabric, Forge, NeoForge, and Quilt have historically used different internal networking APIs. Because of this, a packet written for the Fabric version of a mod won't be recognized by a server running Forge — and vice versa.

Bad Packets solves exactly this problem. The library gives developers a unified way to send and receive packets that works identically across all supported modloaders. Thanks to this, a Fabric client with a mod installed that relies on Bad Packets can connect without errors to a Forge server where the same mod also uses this library.

How Players Use the Mod

Bad Packets is aimed primarily at people installing dependency mods. If a launcher or mod manager reports that another mod requires "Bad Packets," it's enough to download it from Modrinth or CurseForge and place it in the mods folder alongside the main mod. There's no need to open settings menus, type commands, or edit files: the library has no in-game interface, no configuration file, and no commands. All of its work happens in the background whenever another mod calls its functions.

Bad Packets shows up especially often as a required dependency for mods that display extra information about blocks and entities via tooltips, as well as server-client tools that need to sync data between both sides. In CurseForge modpacks, this library is included in thousands of mod packs, making it one of the most widespread library mods in the entire community. At the time of writing, combined downloads from Modrinth and CurseForge exceed forty million.

Compatibility and Platforms

Bad Packets' main strength as a library is its broad platform coverage. The mod is available simultaneously for Fabric, Forge, NeoForge, and Quilt. It supports Minecraft versions from 1.18.2 up through the newest releases in the 1.21 and 26.1 series, and updates for new game versions almost always come out quickly. Bad Packets works on both the client side and the server side; in both environments its presence may be required, depending entirely on how the main mod uses it.

One nuance is worth understanding: Bad Packets doesn't magically make any mods compatible across modloaders. A mod developer who wants to take advantage of this capability has to deliberately integrate its API into their code. In addition, the library doesn't take on more complex tasks like syncing internal game object identifiers between versions for different platforms — that remains the responsibility of the individual mod authors.

Conclusion

Bad Packets is a purely technical mod with no visual effects, new items, or mechanics, but it's exactly this invisible work that makes it one of the key building blocks of modern Minecraft modding. Its main limitation is obvious from the concept itself: a standalone installed library provides no benefit on its own — it only starts working once another mod calls it. It's also worth remembering that Bad Packets doesn't sync more complex game data, such as block or item identifiers, between versions for different modloaders: that part is implemented by mod developers themselves.