Use 3.2.0 for Minecraft 1.7.2/1.6.4/1.6.2/1.5.2/1.4.7 and older

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 developer builds of this project can be acquired at my Jenkins server. These builds have not been approved by the BukkitDev staff. Use them at your own risk.


Please create a ticket 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 developer support 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.


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:

    <name>Comphenix Repository</name>
<!-- 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

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 a ticket if you're having problems. Don't post stack traces in the comments.

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  • Avatar of aadnk aadnk Apr 21, 2014 at 21:31 UTC - 0 likes

    @TNTUP: Go

    It's compiled on my Jenkins server, however, I haven't added the necessary feature yet. I figured I'd wait until I knew you'd be able to run it.

    I'll see if I can't add it soon.

  • Avatar of TNTUP TNTUP Apr 21, 2014 at 19:18 UTC - 0 likes

    @aadnk: Go

    Mhm.. will try but atm im very busy on my server (25-30 per day) and I have less time to do tests :C, and that detetctCME needs to be compiled I guess :P

    EDIT: I did a second /protocol listeners, and heres the newer one:

    Last edited Apr 21, 2014 by TNTUP


  • Avatar of aadnk aadnk Apr 21, 2014 at 14:27 UTC - 0 likes

    @TNTUP: Go

    Well, the error doesn't actually occur in ProtocolLib, the only reason it shows up in the call stack is because I have to "intercept" packet writing in order to implement PacketOutputHandler.

    Even if I knew what caused this, I wouldn't be able to fix it in ProtocolLib. The code (likely in some plugin) that is modifying the NBT tag when Minecraft is iterating over its keys is to blame here.

    So, I still recommend disabling plugins until the problem no longer presents itself (try disabling half of your plugins at a time, if you have many). But this can be difficult, especially if the error only occurs rarely and requires multiple players online, which would limit the usefulness of a test server.

    Perhaps you could try DetectCME instead? I can modify it to also detect cross-thread modification of the NBT tags in PacketPlayOutTileEntityData, if you're interested. Then all you have to do is run this detection plugin, and wait for the error to be triggered.

    @libraryaddict: Go

    I've added this to build #242 (3.4.0-SNAPSHOT) on the Jenkins server. WrappedGameProfile now contains the getter "getProperties()", along with the useful static function WrappedGameProfile.fromPlayer(Player), which allows you to retrieve a game profile from an online player.

  • Avatar of TNTUP TNTUP Apr 20, 2014 at 21:36 UTC - 0 likes

    @aadnk: Go

    I have updated ProtocolLib to 3.3.1, I was on 3.2.0... I'll give out news if its occurs again

    EDIT: Still occurs, maybe its a minecraft bug itself or the plugin, but I can't be sure.

    Last edited Apr 21, 2014 by TNTUP
  • Avatar of aadnk aadnk Apr 19, 2014 at 22:33 UTC - 0 likes

    @libraryaddict: Go

    I suppose I could simply expose it as a WrappedSignedProperty, or someting like that.

    I'll see if I can't implement it tomorrow, when I get back from my vacation.

  • Avatar of libraryaddict libraryaddict Apr 19, 2014 at 14:26 UTC - 0 likes

    Would it be possible to have WrappedGameProfile support getting/setting skin blobs?


  • Avatar of TNTUP TNTUP Apr 19, 2014 at 07:03 UTC - 0 likes

    @aadnk: Go

    Well, players are getting that kind of error while playing ColorShuffle... The developer didn't answers my PM so I could try PM that error, asking him using ProtocolLib...

  • Avatar of aadnk aadnk Apr 18, 2014 at 22:47 UTC - 0 likes

    @PillageCraft: Go

    It's not an error though - it's just an exception that gets thrown when a client forcefully disconnects from the server.

    @TNTUP: Go

    Hm, then the plugin causing this is not actually using ProtocolLib. It might be using TinyProtocol, a drop-in replacement for ProtocolLib, or some equivalent method. Or not - it's very difficult to debug ConcurrentModificationExceptions, especially when you can't reproduce it yourself.

    Do you get this exception almost immediately? If so, try disabling plugins until you no longer get the exception. That should give a clue as to which plugin is causing problems.

  • Avatar of TNTUP TNTUP Apr 18, 2014 at 19:22 UTC - 0 likes

    @aadnk: Go

    Here is it: Does it need to have the plugin running, having players playing it?

    EDIT: I tried, playing the ColorShuffle game, I dont see its name in the commande yyou asked.

    Last edited Apr 18, 2014 by TNTUP
  • Avatar of PillageCraft PillageCraft Apr 18, 2014 at 18:56 UTC - 0 likes

    @aadnk: Go

    That's all it prints in the console. That's the entire stack trace.


Date created
Oct 05, 2012
Last update
Apr 17, 2014
Development stage
  • enUS
GNU General Public License version 2 (GPLv2)
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