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A Clojure plugin for Bukkit-based minecraft servers (Paper, Spigot, Glowstone)

It provides

  • an embedded nREPL server for interactive creative coding
  • Clojure dependency management through deps.edn
  • loading of Clojure-based server modifications at boot


Download the plugin for your server type and version from the releases page, and drop it in your server's plugins/ directory.


The first time you start the server you should see something like this:

[09:33:14 INFO]: [Witchcraft] Enabling Witchcraft v0.0.7
[09:33:14 INFO]: [Witchcraft] Setting PluginClassloader as Context classloader: PluginClassLoader{plugin=Witchcraft v0.0.7, pluginEnabled=true, url=plugins/witchcraft-plugin-0.0.7-for-paper-1.17-shaded.jar}
[09:33:26 INFO]: [Witchcraft] No plugins/witchcraft.edn found, creating default.
[09:33:26 INFO]: [Witchcraft] No deps.edn found, creating default.
[09:33:29 INFO]: [Witchcraft] init: (require (quote lambdaisland.witchcraft))
[09:33:30 INFO]: [Witchcraft] init: (lambdaisland.witchcraft/init-xmaterial!)
[09:33:36 INFO]: nREPL server started on port 25555 on host localhost - nrepl://localhost:25555

Now you can connect with your nREPL-capable editor to port 25555 and start manipulating the game. If you get any errors at this stage please file an issue.

If you are new to Clojure and are unsure which development environment to pick then we recommend Calva for Visual Studio Code. For a fairly complete list of Clojure-capable editors see this overview by


There are two files that are used to configure the plugin, plugins/witchcraft.edn, and deps.edn. Both are in the EDN format (Extensible Data Notation) commonly used in the Clojure world.

plugins/witchcraft.edn is the configuration for the plugin itself. Here you can set things like the nREPL port, or configure code to load when the server starts.

deps.edn is Clojure's way of declaring dependencies, similar to a pom.xml or package.json.

The first time you run the server it will create a deps.edn and plugins/witchcraft.edn. It will also start an nREPL server, and invoke any :init commands you have in your witchcraft.edn.


 {:port 25555
  :middleware [refactor-nrepl.middleware/wrap-refactor
 :init [(require 'lambdaisland.witchcraft)
 :deps true}
  • :nrepl are options passed to nrepl.cmdline/dispatch-commands, if you don't want to run an nREPL server, use :nrepl false
  • :deps can be true (load dependencies from deps.edn), false (don't), or a map with options for tools.deps, e.g. :deps {:aliases [:my-alias]}
  • :init is a sequence of Clojure forms that are evaluated after starting the server. You can use this to load additional Clojure modifications when booting the server


The plugin JAR only bundles Clojure itself (the compiler and core library), nREPL (for interaction), and (for deps.edn support). Any additional dependencies (e.g. nREPL middleware, Witchcraft, clj-minecraft) can be loaded by adding them to deps.edn.

Through deps.edn you can pull in dependencies from Maven/Clojars, or directly from Github. See the Clojure Deps and CLI Guide for how to set up deps.edn.

When no deps.edn is present the plugin will create one on first use, which loads the witchcraft library, as well as the CIDER and refactor-nrepl middlewares for nREPL, which will look something like this:

  {:git/url ""
   :git/sha "..."}
  refactor-nrepl/refactor-nrepl {:mvn/version "2.5.1"}
  cider/cider-nrepl {:mvn/version "0.26.0"}}}

You can use lambdaisland/classpath to reload your deps.edn without having to restart the server. (see lambdaisland.classpath/update-classpath! or!).


To build the plugin yourself you need a recent version of Clojure CLI, see the Clojure getting started guide. You also need Java 16 (earlier versions from Java 12 onwards might work too).

$ clojure --version
Clojure CLI version

$ java -version
openjdk version "16.0.1" 2021-04-20

Then use the build-plugin task, you need to tell it which server you will be using, and the API version.

clojure -T:build-plugin build :server glowstone :api-version 1.12
clojure -T:build-plugin build :server paper :api-version 1.17 
clojure -T:build-plugin build :server spigot :api-version 1.17 

These will create two files each

  • target/witchcraft-plugin-<version>-for-<server>-<api-version>.jar
  • target/witchcraft-plugin-<version>-for-<server>-<api-version>-shaded.jar

It is recommended to use the shaded version. For Glowstone you must use the shaded version. (Naether pulls in an old plexus-utils, which conflicts with tools.deps.alpha).

Copy the plugin jar to your server's plugins directory

$ cp target/witchcraft-plugin-0.0.7-for-paper-1.17-shaded.jar ~/PaperMC/plugins/

Lambda Island Open Source


witchcraft-plugin is part of a growing collection of quality Clojure libraries created and maintained by the fine folks at Gaiwan.

Pay it forward by becoming a backer on our Open Collective, so that we may continue to enjoy a thriving Clojure ecosystem.

You can find an overview of our projects at lambdaisland/open-source.




Everyone has a right to submit patches to witchcraft-plugin, and thus become a contributor.

Contributors MUST

  • adhere to the LambdaIsland Clojure Style Guide
  • write patches that solve a problem. Start by stating the problem, then supply a minimal solution. *
  • agree to license their contributions as MPL 2.0.
  • not break the contract with downstream consumers. **
  • not break the tests.

Contributors SHOULD

  • update the CHANGELOG and README.
  • add tests for new functionality.

If you submit a pull request that adheres to these rules, then it will almost certainly be merged immediately. However some things may require more consideration. If you add new dependencies, or significantly increase the API surface, then we need to decide if these changes are in line with the project's goals. In this case you can start by writing a pitch, and collecting feedback on it.

* This goes for features too, a feature needs to solve a problem. State the problem it solves, then supply a minimal solution.

** As long as this project has not seen a public release (i.e. is not on Clojars) we may still consider making breaking changes, if there is consensus that the changes are justified.


Copyright © 2021 Arne Brasseur and Contributors

Licensed under the term of the Mozilla Public License 2.0, see LICENSE.

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