Use 3.4.0 for Minecraft 1.7.10 and older

Use 3.6.x for Spigot 1.8

Users of MCPC-Plus 1.7.2 and above should look for a special build (ProtocolLib - MCPC 1.7.2) on my Jenkins server. Cauldron users should download ProtocolLib - Cauldron.

Certain tasks are impossible to perform with the standard Bukkit API, and may require working with and even modify Minecraft directly. A common technique is to modify incoming and outgoing packets, or inject custom packets into the stream. This is quite cumbersome to do, however, and most implementations will break as soon as a new version of Minecraft has been released, mostly due to obfuscation.

Critically, different plugins that use this approach may hook into the same classes, with unpredictable outcomes. More than often this causes plugins to crash, but it may also lead to more subtle bugs.

Up-to-date development builds of ProtocolLib can be found here:
Older development builds (and Cauldron builds) can be found here:
These builds have not been approved by the BukkitDev staff. Use them at your own risk.


Please create a issue with as much information as possible if you experience a problem that has not already been reported. Comments with a huge stack trace will be deleted.

If you need help with the API, please use the Spigot discussion forum. If your question cannot be made public for whatever reason (including security bugs), send me a personal message instead.

For server operators

Just download ProtocolLib from the link above. It doesn't do anything on its own, it simply allows other plugins to function.


  • Why do I get FieldAccessExceptions when I try to read or write from packets?

The reason for these exceptions is because ProtocolLib is not using the packet format as described on the Wiki, it's using the in-memory representation of these packets. Often, the in-memory representation will use integers instead of shorts and bytes, and store more complex objects (like ItemStacks) directly.

You can figure out the in-memory representation from the Minecraft source code, or just use PacketWrapper where I've done all that work for you.


Source code for a bunch of example programs that use ProtocolLib can be found at this thread on the main support forum.

You may also be interested in PacketWrapper, a library that makes it possible to modify a packet without having to decompile the Minecraft source code.

Finally, for the more advanced users who want to use ProtocolLib if present, but still fall back on their own packet listening system, I recommend taking a look at this thread. I explain where and how to inject code into CraftBukkit in order to intercept sent and received packets yourself.

Maven repository

If you're using Maven, you'll be able to automatically download the JAR, JavaDoc and associated sources from the following repository:

<!-- And so on -->

This repository contains ProtocolLib, TagHelper and BlockPatcher. You can add any of them as a dependency like so:




Main administrative command. Supports the following sub-commands:

  • config: Reload the configuration file.
  • check: Check for new versions on BukkitDev.
  • update: Check for new versions and automatically download the JAR. The server must be restarted for this to take effect.
  • timings: Toggle measuring the amount of CPU time spent by each plugin. See here for more information.
  • listeners: Display what plugins are using ProtocolLib, and the packet types they are intercepting.

All of these commands require the permission protocol.admin.


/protocol update


Add or remove a debug packet listener. This is useful for plugin authors who just wants to see when a packet is sent, and with what content.

Sub commands:

  • add: Add a packet listener with a given packet ID.
  • remove: Remove one or every packet listener with the given packet IDs.
  • names: Print the name of every given packet ID.

Parameters (in order):

  1. Connection side: Either client or server.
  2. Multiple ID ranges: Can be a single packet ID like 14, or a range like 10 - 15. Defaults to 0 - 255 if not specified.
  3. Detailed: If TRUE, prints the full packet content.


/packet add client 10-13 true

For 3.0.0 and above, you should specify the protocol, sender and name instead:

/packet add play server chat true

In 3.4.0-SNAPSHOT and above, you can also display the packet before its modified by any packet listeners:

/packet add play server chat compare

Remove all listeners:

/packet remove client
/packet remove server

Note that this command should rarely be used on a production server. Listening to too many packets may crash the server.


The filter system (introduced in 2.4.1) uses the built in JavaScript interpreter in JVM 6 (Rhino) to extend the packet command with filtering capabilities - it is now possible to, say, only print entity metadata packet events (packet add server 40) for a given entity ID:

> packet add server 40 true
Added listener ListeningWhitelist{priority=MONITOR, packets=[40]}
> filter add entity_filter 40
Enter filter program ('}' to complete or CANCEL):
function(event, packet) {
>   return packet.a == 1000; 
Added filter entity_filter.

This should be much more convenient than having to compile a test plugin and reload the whole server. Note that this feature is disabled by default for security reasons. To enable it, add "debug: true" to config.yml.


A small set of configuration options are available:

Global section



auto updater.notifytrueInform any player with the permission when a new version of ProtocolLib is out.
auto updater.downloadtrueAutomatically download and install the newest version of ProtocolLib. The installation will take effect when the server restarts.
auto updater.delay43200The number of seconds between each check for a new update.
auto updater.last0This simply records the last time (in seconds since 01.01.1970) an update check was performed. Set it to 0 to force a new update check.
metricstrueIf TRUE, ProtocolLib will publish anonymous usage data to Set it to FALSE to opt-out.
background compilertrueIf TRUE, ProtocolLib will try and improve performance by replacing reflection with compiled code on-the-fly.
ignore version checkNoneForce ProtocolLib to start for a specified Minecraft version, even if it is incompatible.
suppressed reportsNoneIf any error or warning report is present in this list, they will not appear in the console or the log.

For more information, take a look at the default configuration file.

Tutorial for developers

See this page for more information.


One of the main goals of this project was to achieve maximum compatibility with CraftBukkit. And the end result is quite good - in tests I successfully ran an unmodified ProtocolLib on CraftBukkit 1.8.0, and it should be resilient against future changes. It's likely that I won't have to update ProtocolLib for anything but bug and performance fixes.

How is this possible? It all comes down to reflection in the end. Essentially, no name is hard coded - every field, method and class is deduced by looking at field types, package names or parameter types. It's remarkably consistent across different versions.

Plugins that appear to be compatible

Plugins known to be compatible

  • SpoutPlugin

Plugins using ProtocolLib

Inactive projects

Please let me know if you want me to add your plugin to this list. :)


This plugin uses MCStats to generate and publish anonymous aggregate usage statistics, but you can easily opt-out by setting metrics in config.yml to false.

If enabled, the following is sent every ten minutes:

  • Metrics revision version (currently 6).
  • Server's GUID
  • Players currently online (not max player count)
  • Server version string (the same version string you see in /version)
  • Current version of ProtocolLib
  • The name of every plugin that registers a packet listener in ProtocolLib.


I would like to thank everyone who has donated to ProtocoLib. I really appreciate it. :)


ProtocolLib Statistics

Note: Create an issue if you're having problems. Don't post stack traces in the comments.

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  • Avatar of hutt132 hutt132 Mar 28, 2015 at 06:59 UTC - 1 like

    The dev build download page is down.

  • Avatar of MineCraftMyph MineCraftMyph Mar 25, 2015 at 11:37 UTC - 0 likes
    • ERROR

    [11:34:57] [Server thread/ERROR]: Could not pass event PlayerQuitEvent to ProtocolLib v3.6.3-SNAPSHOT org.bukkit.event.EventException at$1.execute( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at org.bukkit.plugin.RegisteredListener.callEvent( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at org.bukkit.plugin.SimplePluginManager.fireEvent( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at org.bukkit.plugin.SimplePluginManager.callEvent( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.PlayerList.disconnect( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.PlayerConnection.a( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.NetworkManager.l( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.ServerConnection.c( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.MinecraftServer.A( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.DedicatedServer.A( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at net.minecraft.server.v1_8_R2.MinecraftServer.z( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] at Source) [?:1.8.0_31] Caused by: java.lang.NoClassDefFoundError: Could not initialize class com.comphenix.protocol.injector.PacketConstructor at com.comphenix.protocol.injector.BukkitUnwrapper.unwrapItem( [?:?] at com.comphenix.protocol.utility.MinecraftFields.getNetworkManager( [?:?] at com.comphenix.protocol.injector.netty.InjectionFactory.fromPlayer( [?:?] at com.comphenix.protocol.injector.netty.NettyProtocolInjector$4.handleDisconnect( [?:?] at com.comphenix.protocol.injector.PacketFilterManager.onPlayerQuit( [?:?] at com.comphenix.protocol.injector.PacketFilterManager.access$800( [?:?] at com.comphenix.protocol.injector.PacketFilterManager$4.onPlayerQuit( [?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [?:1.8.0_31] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) [?:1.8.0_31] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) [?:1.8.0_31] at java.lang.reflect.Method.invoke(Unknown Source) [?:1.8.0_31] at$1.execute( [minecraft_server.jar:git-Spigot-4b89e7b-7d0f836] ... 12 more

  • Avatar of aadnk aadnk Mar 18, 2015 at 18:14 UTC - 0 likes

    @fly3949: Go

    Sorry, looks like Apache crashed on my web server. It's up-to-date and running now.

    @MrGrieferHGTech: Go

    I'm no longer working on ProtocolLib. You should direct any questions to dmulloy2.

    But ProtocolLib should work with 1.8.0-3, you just need to use the correct version.

  • Avatar of TrewCraft360 TrewCraft360 Mar 17, 2015 at 22:20 UTC - 0 likes

    Please update to 1.8.1

  • Avatar of fly3949 fly3949 Mar 14, 2015 at 04:58 UTC - 0 likes

    Where is "ProtocolLib - Cauldron"? I can't open the website.

    Last edited Mar 14, 2015 by fly3949
  • Avatar of John00708 John00708 Feb 24, 2015 at 19:59 UTC - 0 likes

    Guys, for everyone who asks for ProtocolLib for 1.8, you can find it here:

    public void onPlayerFartEvent(PlayerFartEvent e){
    	e.getPlayer.sendMessage(ChatColor.DARK_RED + "You Farted!");
  • Avatar of Corandevus Corandevus Feb 19, 2015 at 17:48 UTC - 0 likes

    Hello,Sorry for my very bad english. I have spigot 1.8 done with the latest buildtool, and once (or twice) a day I have all players instantly freezing and "bugging". They are freezing and can't move, but disabling ProtocolLib remove this issue. I tried to disabling all other plug-in associated with ProtocolLib but nothing happens. The only way to solve the problem is, like i said, disabling ProtocolLib. This happens "randomly" around 3pm-7pm (+1GMT) On the console nothing happens: only a lot of fake warnings for "cheating" players from NoCheatPlus (We tried to disable NCP, but the "freeze-bug" still happen during evening). The Console seems to "ignore" that bug. The TPS are good, CPU and RAM are normal, when this happens. I realy need some help, please.

  • Avatar of MrGrieferHGTech MrGrieferHGTech Feb 12, 2015 at 12:41 UTC - 0 likes

    @aadnk: Go

    Can you update ProtocolLib to 1.8.1?

  • Avatar of INSTANTOUT INSTANTOUT Feb 10, 2015 at 19:10 UTC - 0 likes

    "Use 3.6.x for Spigot 1.8" Where Is This Part At? Cause i dont See the download...

  • Avatar of aadnk aadnk Feb 07, 2015 at 21:26 UTC - 0 likes

    @sakura_blades: Go

    Remove TagAPI - it does not work (and never will) in 1.8.


Date created
Oct 05, 2012
Last update
Jun 15, 2014
Development stage
  • enUS
GNU General Public License version 2 (GPLv2)
Curse link
Recent files