The only requirement to use CIDER is to have an nREPL server to which it may connect. Many Clojurians favour the use of tools like Leiningen, Boot or Gradle to start an nREPL server, but the use of one of them is not a prerequisite to use CIDER.

Setting up a Clojure project (optional)

CIDER features a command called cider-jack-in that will start an nREPL server for a particular Clojure project and connect to it automatically. Most popular Clojure project management tools are supported by default - namely Leiningen, Boot, clj (tools.deps) and Gradle.


This functionality depends on Leiningen 2.5.2+ or Boot 2.7.0+. Older versions are not supported.

Let's create a simple Clojure project using Leiningen now. Provided you've installed it already, all you need to do is:

$ lein new demo

The two main ways to obtain an nREPL connection are discussed in the following sections of the manual.

Launch an nREPL server and client from Emacs

Simply open in Emacs a file belonging to your project (like foo.clj) and type M-x cider-jack-in RET. This will start an nREPL server and CIDER will automatically connect to it.


If it is a lein, boot or tools.deps (deps.edn) project nREPL will be started with all dependencies loaded. Dependency auto-injection is currently not supported for Gradle projects.

Alternatively you can use C-u M-x cider-jack-in RET to specify the name of a lein, boot or tools.deps project, without having to visit any file in it. This option is also useful if your project contains some combination of project.clj, build.boot and deps.edn and you want to launch a REPL for one or the other.


In Clojure(Script) buffers the command cider-jack-in is bound to C-c C-x (C-)j (C-)j.

For further customizing the command line used for cider-jack-in, you can change the following (all string options):

  • cider-lein-global-options, cider-boot-global-options, cider-clojure-cli-global-options, cider-gradle-global-options: these are passed to the command directly, in first position (e.g. -o to lein enables offline mode).
  • cider-lein-parameters, cider-boot-parameters, cider-clojure-cli-parameters, cider-gradle-parameters: these are usually tasks names and their parameters (e.g.: dev for launching boot's dev task instead of the standard repl -s wait).

Note that if you try to run cider-jack-in outside a project directory normally you'd get a warning to confirm you really want to do this, as more often than not you'd probably do this accidentally. If you decide to proceed, CIDER will invoke the command configured in cider-jack-in-default. This used to be lein prior to CIDER 0.17 and it was switched to Clojure's CLI (clj) afterwards.


You can set cider-allow-jack-in-without-project to t if you'd like to disable the warning displayed when jacking-in outside a project.

Connect to a running nREPL server

Go to your project's directory in a terminal and type there:

$ lein repl :headless

Or for boot:

$ boot repl -s wait (or whatever task launches a repl)

It is also possible for plain clj, although the command is somewhat longer:

$ clj -Sdeps '{:deps {nrepl {:mvn/version "0.4.5"} cider/cider-nrepl {:mvn/version "0.18.0"}}}' -m nrepl.cmdline --middleware "[cider.nrepl/cider-middleware]"

Alternatively you can start nREPL either manually or by the facilities provided by your project's build tool (Gradle, Maven, etc).

After you get your nREPL server running, go back to Emacs. Type there M-x cider-connect RET to connect to the running nREPL server.


In Clojure(Script) buffers the command cider-connect is bound to C-c C-x c s.

You can configure known endpoints used by the cider-connect command offered via a completing read. This is useful if you have a list of common host/ports you want to establish remote nREPL connections to. Using an optional label is helpful for identifying each host.

(setq cider-known-endpoints
  '(("host-a" "" "7888")
    ("host-b" "7888")))