Use 3.4.0 for Minecraft 1.7.9/.7.2/1.6.4/1.6.2/1.5.2/1.4.7 and older

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 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.


  • 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:

    <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

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

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  • Avatar of delsolsi213 delsolsi213 Jul 14, 2014 at 01:23 UTC - 0 likes

    @aadnk: Go

    yeah i was using 103 could be cauldron causing it on that version, i have protocl disabled i will enable and test on both versions, if its fixed in 107 ill tell you either way.

  • Avatar of aadnk aadnk Jul 13, 2014 at 13:53 UTC - 0 likes

    @delsolsi213: Go

    Hm, unfortunately, I'm unable to reproduce this on a Cauldron #107 server with Pixelmon, NBTEdit, ProtocolLib and ItemRenamer either.

    What is the output of these commands by the way:

    • /protocol listeners
    • /tps
  • Avatar of delsolsi213 delsolsi213 Jul 12, 2014 at 17:34 UTC - 0 likes

    @aadnk: Go

    eh i have cauldron 103, maybe it was an issue with them? i will update it to 107 and test it, and yes i removed protocollib and the rubber banding stopped (thats how my players called it xD) and with it enabled it happened.

    I forgot to mentiont he mods im using is pixelmon and nbtedit mod.

    Last edited Jul 12, 2014 by delsolsi213
  • Avatar of aadnk aadnk Jul 12, 2014 at 13:32 UTC - 0 likes

    @delsolsi213: Go

    Have you tried removing ProtocolLib completely, and check if you still experience the same problem? And what do you get when you run the command "/protocol listeners"?

    I'm unable to reproduce this with Cauldron 107 and Forge #1147 (with ProtocolLib and ItemRenamer), however. So, if ProtocolLib is triggering it, it must be in conjuction with some other plugin and mod. I'd need a list of those to be able to reproduce this problem, and thus be able to fix it.

    Could you create a ticket, by the way? This issue is getting too complicated for the comment section.

    @EddieFriday: Go

    ProtocolLib is a library plugin, and doesn't do very much on its own. Disabling it will cause other plugins to disable parts of their functionality, or be disabled altogether.

    You can figure out which of your plugins are actually using ProtocolLib by running the command "/protocol listeners". It will contain a list of all the packet listeners currently registered, along with the name of the associated plugins.

    Try disabling all the plugins on this list, while keeping ProtocolLib running. See if the problem persists - if not, gradually enable the plugins on this list until the problem reappears.

    If, on the other hand, the problem is still present even after disabling all the other plugins, then ProtocolLib must be to blame. In that case, please create a ticket with as much information as you can provide: Bukkit version, plugin list with names and versions, and so on.

  • Avatar of EddieFriday EddieFriday Jul 12, 2014 at 12:27 UTC - 0 likes

    @aadnk: Go

    No i'm using Bukkit.

    I have another problem with protocollib.

    When I login other players will be kicked from the server and I will be kicked last. Why is this happening? When I remove the Plugin from the Plugin Folder, It will be working fine..

    Do you have any solution to this why when I add protocollib it will kick us all?

  • Avatar of delsolsi213 delsolsi213 Jul 11, 2014 at 17:15 UTC - 0 likes

    @aadnk: Go

    only plugin i use that depends on protocol lib is itemrenamer and one to hide my list, i tried it with only your plugin enabled and it is infact the one causing it, it also causes blocks 1 place to dissapear or when you break blocks to glitch i honestly dont know why, sadly it doesnt throw any errors either. using cauldron version 103 btw.

  • Avatar of aadnk aadnk Jul 11, 2014 at 16:19 UTC - 0 likes

    @EddieFriday: Go

    CraftBukkit #3103 is working fine here.

    Are you using Spigot by any chance? Build #1545 is not compatible with ProtocolLib, so you'll have to upgrade to Spigot #1550.

  • Avatar of aadnk aadnk Jul 11, 2014 at 16:12 UTC - 0 likes

    @delsolsi213: Go

    What plugins are you running? Of whose, which depend on ProtocolLib? I find it unlikely ProtocolLib itself is causing this, especially if you're using Cauldron 1.7.2.

    Have you checked the tick per seconds rate, too? It might be running too low.

  • Avatar of EddieFriday EddieFriday Jul 11, 2014 at 12:26 UTC - 2 likes

    Please support 1.7.10

  • Avatar of delsolsi213 delsolsi213 Jul 11, 2014 at 01:24 UTC - 0 likes

    @aadnk: Go

    Hi, using your plugin on a cauldron server causes my players to rubber band, they get stuck at times and get teleported back. no console errors either.


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