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 Leiningen or Boot project (optional)

[Leiningen](https://leiningen.org) is the de-facto standard build/project
management tool for Clojure. [Boot](http://boot-clj.com) is a newer build tool
offering abstractions and libraries to construct more complex build
scenarios. Both have a similar scope to the Maven build tool favoured by Java
developers (and they actually reuse many things from the Maven ecosystem).

CIDER features a command called `cider-jack-in` that will start an nREPL server
for a particular Leiningen or Boot project and connect to it automatically.
This functionality depends on Leiningen 2.5.2+ or Boot
2.7.0+. Older versions are not supported. For Leiningen, follow the installation
instructions on its web site to get it up and running and afterwards create a
project like this:

```
$ 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
<kbd>M-x</kbd> `cider-jack-in` <kbd>RET</kbd>. 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.

Alternatively you can use <kbd>C-u M-x</kbd> `cider-jack-in` <kbd>RET</kbd> 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.


!!! Tip

    In Clojure(Script) buffers the command `cider-jack-in` is bound to <kbd>C-c M-j</kbd>.

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-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-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`).

## Connect to a running nREPL server

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

```
$ lein repl
```

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 {cider/cider-nrepl {:mvn/version "0.18.0-SNAPSHOT"} }}' -e '(require (quote cider-nrepl.main)) (cider-nrepl.main/init ["cider.nrepl/cider-middleware"])'
```

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

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

!!! Tip

    In Clojure(Script) buffers the command `cider-connect` is bound to <kbd>C-c M-c</kbd>.

!!! Tip

    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" "10.10.10.1" "7888")
        ("host-b" "7888")))
    ```