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A collection of nREPL middleware originally designed to enhance CIDER.

If you're just a user trying to get started with CIDER, then you probably don't want to read this. You should follow the steps in CIDER's manual instead.

If you're trying to use cider-nrepl for some other purpose, the sections below outline how to include it in a project.

People who are new to nREPL might benefit from reading its manual.


This section documents some of the major design decisions in cider-nrepl.

While in essence it's just a collection of nREPL middleware we had to make a few important design decision here and there that influenced the code base and the usability of cider-nrepl in various ways.

Editor Agnostic

Although those middlewares were created for use with CIDER almost all of them are extremely generic and can be leveraged from other editors.

Projects like vim-fireplace and vim-replant are making use of cider-nrepl already.

Isolated Runtime Dependencies

All of cider-nrepl's dependencies are processed with mranderson, so that they won't collide with the dependencies of your own projects. This basically means that cider-nrepl doesn't have any runtime dependencies in the production artifact - just copies of the deps inlined with changed namespaces/packages. It's a bit ugly and painful, but it gets the job done.

If someone has better ideas how to isolate our runtime dependencies - we're all ears!

Deferred Middleware Loading

To improve the startup time of the nREPL server all of cider-nrepl's middlewares are loaded for real only when needed.

You can read more about this here.

We'd love to bring the support for deferred middleware loading straight to nREPL down the road.

Middleware Errors Never Hang Requests

See here.

Reusable Core Logic

cider-nrepl tries to have as little logic as possible and mostly provides thin wrappers over existing libraries (e.g. compliment, cljfmt, etc). Much of its core functionality lives in orchard, so that eventually it can be used by non-nREPL clients (e.g. Socket REPL clients).

Very simply put - there's very little code in cider-nrepl that's not simply wrapping code from other libraries in nREPL operations.

The primary reason for this is our desire to eventually provide support for non-nREPL REPLs in CIDER, but this also means that other editors can directly leverage the work we've done so far.

ClojureScript Support

We want cider-nrepl to offer feature parity between Clojure and ClojureScript, but we're not quite there yet and many features right now are Clojure-only.

We'd really appreciate all the help we can get from ClojureScript hackers to make this a reality.



cider-nrepl supports only Clojure(Script) 1.8+ and Java 8+.

Leiningen users will need to have version 2.8.3 or newer installed. Boot users will need to have version 2.8.2 or newer installed.

Via Leiningen

Use the convenient plugin for defaults, either in your project's project.clj file or in the :user profile in ~/.lein/profiles.clj.

:plugins [[cider/cider-nrepl "0.21.1"]]

A minimal profiles.clj for CIDER would be:

{:user {:plugins [[cider/cider-nrepl "0.21.1"]]}}

Or (if you know what you're doing) add cider-nrepl to your :dev :dependencies vector plus specific middleware to :nrepl-middleware under :repl-options.

:dependencies [[cider/cider-nrepl "0.21.1"]]
:repl-options {:nrepl-middleware

Note that you should use a cider-nrepl version compatible with your CIDER. Generally, if you're using CIDER 0.x.y you should be using cider-nrepl 0.x.y, if you're using CIDER 0.x.y-SNAPSHOT, you should be using cider-nrepl 0.x.y-SNAPSHOT, etc.

Via Boot

Boot users can configure the injected middleware by either specifying it on the command line through the cider.tasks/add-middleware task (the lenghty command below will include the apropos and version functionality):

boot -d nrepl:0.6.0 -d cider/cider-nrepl:0.21.1 -i "(require 'cider.tasks)" cider.tasks/add-middleware -m cider.nrepl.middleware.apropos/wrap-apropos -m cider.nrepl.middleware.version/wrap-version cider.tasks/nrepl-server wait

Or for all of their projects by adding a ~/.boot/profile.boot file like so:

(set-env! :dependencies '[[nrepl "0.6.0"]
                          [cider/cider-nrepl "0.21.1"]])

(require '[cider.tasks :refer [add-middleware nrepl-server]])

(task-options! add-middleware {:middleware '[cider.nrepl.middleware.apropos/wrap-apropos

And then launching boot add-middleware nrepl-server wait.

Note that this is not necessary when using the standard cider-jack-in.

For more information visit boot-clj wiki.

Via clj

You can easily boot an nREPL server with the CIDER middleware loaded with the following "magic" incantation:

clj -Sdeps '{:deps {cider/cider-nrepl {:mvn/version "0.21.1"} }}' -m nrepl.cmdline --middleware "[cider.nrepl/cider-middleware]"

There are also two convenient aliases you can employ (see this project's deps.edn):

 {:cider-clj {:extra-deps {org.clojure/clojure {:mvn/version "1.9.0"}
                           cider/cider-nrepl {:mvn/version "0.21.1"}}
              :main-opts ["-m" "nrepl.cmdline" "--middleware" "[cider.nrepl/cider-middleware]"]}

  :cider-cljs {:extra-deps {org.clojure/clojure {:mvn/version "1.9.0"}
                            org.clojure/clojurescript {:mvn/version "1.10.339"}
                            cider/cider-nrepl {:mvn/version "0.21.1"}
                            cider/piggieback {:mvn/version "0.4.0"}}
               :main-opts ["-m" "nrepl.cmdline" "--middleware"

Which then allow you to simply run:

clj -A:cider-clj

Note that clj was introduced in Clojure 1.9.

Via embedding nREPL in your app

If you're embedding nREPL in your application you'll have to start the server with CIDER's own nREPL handler.

(ns my-app
  (:require [nrepl.server :as nrepl-server]))

(defn nrepl-handler []
  (require 'cider.nrepl)
  (ns-resolve 'cider.nrepl 'cider-nrepl-handler))

(defn -main []
  (nrepl-server/start-server :port 7888 :handler (nrepl-handler)))

(See issue #447 for why the manual namespace resolution of cider-nrepl-handler is currently necessary.)

With JBoss AS/JBoss EAP/WildFly

Using the advanced features of the info middleware with one of the JBoss application servers requires a tweak, since JBoss modules prevent modifications to AppClassLoader (usually the highest modifiable classloader) from being seen by application code. To work around this, run the following code from within your application to mark that classloader as unmodifiable, and cause the lower level clojure.lang.DynamicClassLoader to be used instead. This code must execute prior to loading the cider-nrepl middleware. Note that this is only if you are deploying a standard WAR file to the application server directly. If you are using Immutant (1.x or 2.x), you won't need to do this.

(require '[dynapath.dynamic-classpath :as cp])

(extend sun.misc.Launcher$AppClassLoader
  (assoc cp/base-readable-addable-classpath
    :classpath-urls #(seq (.getURLs %))
    :can-add? (constantly false)))

Supplied nREPL middleware

Middleware Op(s) Description
wrap-apropos apropos Pattern search for symbols and documentation.
wrap-classpath classpath Java classpath.
wrap-complete complete Simple completion. Supports both Clojure & ClojureScript.
wrap-debug init-debugger/debug-input Establish a channel for cider-debug commands, use it to get debug input, and also wrap the eval op.
wrap-format format-(code/edn) Code and data formatting.
wrap-info info/eldoc File/line, arglists, docstrings and other metadata for vars.
wrap-inspect inspect-(start/refresh/pop/push/reset/get-path) Inspect a Clojure expression.
wrap-macroexpand macroexpand/macroexpand-1/macroexpand-all/macroexpand-step Macroexpand a Clojure form.
wrap-ns ns-list/ns-vars/ns-path/ns-load-all/ns-aliases Namespace browsing & loading.
wrap-spec spec-list/spec-form/spec-example Spec browsing.
wrap-profile toggle-profile/toggle-profile-ns/is-var-profiled/profile-summary/profile-var-summary/clear-profile/get-max-samples/set-max-samples Provides profiling support based on the profile library.
wrap-refresh refresh/refresh-all/refresh-clear Code reloading.
wrap-resource resource Return resource path.
wrap-stacktrace stacktrace Cause and stacktrace analysis for exceptions.
wrap-test test-var-query/retest/test-stacktrace Test execution, reporting, and inspection.
wrap-trace toggle-trace-var/toggle-trace-ns Toggle tracing of a given var or ns.
wrap-out out-subscribe/out-unsubscribe Echo the server's output stream to client sessions.
wrap-undef undef Undefine a var.
wrap-version cider-version The CIDER-nREPL version map.

Release policy

We’re following SemVer (as much as one can be following it when the major version is 0). At this point bumps of the minor (second) version number are considered major releases and always include new features or significant changes to existing features. API compatibility between major releases is not a (big) concern (although we try to break the API rarely and only for a good reason).

The development cycle for the next major release starts immediately after the previous one has been shipped. Bugfix/point releases (if any) address only serious bugs and never contain new features.

Note: Prior to cider-nrepl 0.18, CIDER and cider-nrepl releases were always done in sync. As most editors started relying on cider-nrepl this was eventually changed and now cider-nrepl releases happen on their own schedule.



For questions, suggestions and support refer to our official mailing list or the Freenode channel #clojure-emacs. Please, don't report issues there, as this makes them harder to track.


Report issues and suggest features and improvements on the GitHub issue tracker. Don't ask questions on the issue tracker - the mailing list and the IRC channel are the places for questions.


Patches under any form are always welcome! GitHub pull requests are even better! :-)

Before submitting a patch or a pull request make sure all tests are passing and that your patch is in line with the contribution guidelines.

Working with mranderson (inlining runtime dependencies)

mranderson is used to avoid classpath collisions.

To work with mranderson the first thing to do is:

lein do clean, inline-deps

This creates the munged local dependencies in target/srcdeps directory.

After that you can run your tests or your REPL with:

lein with-profile +plugin.mranderson/config repl
lein with-profile +plugin.mranderson/config test

Note the + sign before the leiningen profile. For this leiningen profile to work you need leiningen version 2.5.0+! If you want to use mranderson while developing locally with the REPL the source has to be modified in the target/srcdeps directory. When you want to release locally:

lein with-profile plugin.mranderson/config install

Release to clojars:

lein with-profile plugin.mranderson/config deploy clojars

Or you can use the Makefile as:

make clean
make install
make deploy

Hall of Fame

Special credit goes to the following people for their contributions:

And a big thanks to all other contributors who have helped so far.

Let's also acknowledge some of the projects leveraged by cider-nrepl:

  • orchard - extracted from cider-nrepl, so that non-nREPL clients can leverage the generic tooling functionality (like inspect, apropos, var-info, etc
  • compliment - for Clojure code completion
  • cljs-tooling - for ClojureScript code completion and var info
  • tools.trace - for tracing
  • tools.namespace - for namespace reloading
  • cljfmt - for code formatting


Copyright © 2013-2019 Bozhidar Batsov

Distributed under the Eclipse Public License, the same as Clojure.