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REPL Jack-in and Connect Sequences#

Many projects grow out of the template phase and call for custom developer workflows involving application start commands, customized REPLs, and what have you. Even some templates add this kind of complexity. To make Jack-in usable for a broader set of projects, Calva has a setting keyed calva.replConnectSequences which lets you configure one ore more connect sequences.

NB: Connect sequence configuration affects Calva's Jack-in menu in the following ways:

  1. With no sequence configured, Calva will prompt for the built-in sequences it has that seems to match your project.
  2. When any number of connection sequences are configured, Calva will prompt for your custom sequences, as well as the built-in sequences. Whether built-in or custom, only sequences relevant to your project will be included in the prompt.

Settings for adding Custom Sequences#

A connect sequence configures the following:

  • name: (required) This will show up in the Jack-in quick-pick menu when you start Jack-in (see above).
  • projectType: (required) This is either "Leiningen”, "deps.edn", "shadow-cljs", "lein-shadow", "Gradle", ”generic”, or "custom".
  • autoSelectForJackIn: A boolean. If true, this sequence will be automatically selected at Jack-in, suppressing the Project Type. Use together with projectRootPath to also suppress the Project Root menu. Add usage of menuSelections to go for a prompt-less REPL Jack-in. If you have more than one sequence with autoSelectForJackIn set to true, the first one will be used.
  • autoSelectForConnect: A boolean. If true, this sequence will be automatically selected at Connect, suppressing the Project Type menu. Use together with projectRootPath to also suppress the Project Root menu. If you have more than one sequence with autoSelectForConnect set to true, the first one will be used.
  • projectRootPath: An array of path segments leading to the root of the project to which this connect sequence corresponds. Use together with autoSelectForJackIn/autoSelectForConnect to suppress the Project Root menu. The path can be absolute or relative to the workspace root. If there are several Workspace Folders, the workspace root is the path of the first folder, so relative paths will only work for this first folder.
  • nReplPortFile: An array of path segments with the project root-relative path to the nREPL port file for this connect sequence. E.g. For shadow-cljs this would be [".shadow-cljs", "nrepl.port"].
  • afterCLJReplJackInCode: Code to evaluate in the CLJ REPL once it has been created. You can use either a string or an array of strings. If you use an array, the strings will be joined with a newline character to form the resulting code.
  • customJackInCommandLine: A string with a command line that should be used to launch the REPL. See Custom Command Line, below.
  • cljsType: This can be either "Figwheel Main", "shadow-cljs", "ClojureScript built-in for browser", "ClojureScript built-in for node", "lein-figwheel", "none", or a dictionary configuring a custom type. If set to "none", Calva will skip connecting a ClojureScript repl. A custom type has the following fields:
    • dependsOn: (required) Calva will use this to determine which dependencies it will add when starting the project (Jacking in). This can be either "Figwheel Main", "shadow-cljs", "ClojureScript built-in for browser", "ClojureScript built-in for node", "lein-figwheel", or ”User provided”. If it is "User provided", then you need to provide the dependencies in the project or launch with an alias (deps.edn), profile (Leiningen), or build (shadow-cljs) that provides the dependencies needed.
    • isStarted: Boolean. For CLJS REPLs that Calva does not need to start, set this to true. (If you base your custom cljs repl on a shadow-cljs workflow, for instance.)
    • startCode: Clojure code to be evaluated to create and/or start your custom CLJS REPL.
    • isReadyToStartRegExp: A regular expression which, when matched in the stdout from the startCode evaluation, will make Calva continue with connecting the REPL, and to prompt the user to start the application. If omitted and there is startCode Calva will continue when that code is evaluated.
    • openUrlRegExp: A regular expression, matched against the stdout of cljsType evaluations, for extracting the URL with which the app can be started. The expression should have a capturing group named url. E.g. "Open URL: (?\<url>S+)"
    • shouldOpenUrl: Choose if Calva should automatically open the URL for you or not.
    • connectCode: (required) Clojure code to be evaluated to convert the REPL to a CLJS REPL that Calva can use to connect to the application. (For some setups this could also conditionally start the CLJS REPL. If so: startCode should be omitted.)
    • isConnectedRegExp: (required) A regular expression which, when matched in the stdout from the connectCode evaluation, will tell Calva that the application is connected. The default is To quit, type: :cljs/quit and you should leave it at that unless you know it won't work.
    • printThisLineRegExp: regular expression which, when matched in the stdout from any code evaluations in the cljsType, will make the matched text be printed to the Output window.
    • buildsRequired: Boolean. If the repl type requires that builds are started in order to connect to them, set this to true.
  • menuSelections: a dictionary with pre-filled-in selections for the Jack-in and Connect prompts, making Calva not prompt for that particular selection:
    • leinProfiles: At Jack-in to a Leiningen project, use these profiles to launch the repl.
    • leinAlias: At Jack-in to a Leiningen project, launch with this alias. Set to null to launch with Calva's default task (a headless repl), w/o prompting.
    • cljAliases: At Jack-in to a deps.edn project, use these aliases to launch the repl.
    • cljsLaunchBuilds: The cljs builds to start/watch at Jack-in/connect.
    • cljsDefaultBuild: Which cljs build to attach to at the initial connect.
  • jackInEnv: An object with environment variables that will be merged with the global calva.jackInEnv and then applied to the Jack-in process. The merge is very similar to how Clojure's merge works. So for any common keys between the global setting and this one, the ones from this setting will win.

The Calva built-in sequences also use this format, check them out to get a clearer picture of how these settings work.

Force the project type menu to show

The convenience of autoSelectForJackIn/Connect can be an inconvenience when you want to use another project type/sequence for a project. For this reason, the calva.connect and calva.jackIn can be provided with an option disableAutoSelect, which forces the project root and project type menus to show. See Options for the Connect Command and Options for the Jack-in Command for more on this.

Path segments

projectRootPath and nReplPortFile both take an array of path segments. This is to make the paths work cross-platform. If you can't be bothered splitting up the path in segments, put the whole path in the first segment, though please note that if you use Windows path separators, these will not work for users with Linux or macOS.

Custom Command Line#

Custom command lines are there to bridge the gap to those situations where standard Jack-in command lines don't reach. Like:

  1. You want to provide command line options to a supported tool, which Jack-in does not provide
  2. Your project has some script through which it is started
  3. The REPL is provided by some tool that Calva does not know of
  4. Any other reason...

A custom command line is executed from same directory as the REPL project root (See projectRootPath, above), and can be as simple as my-repl-jack-in-command. You can use a relative or absolute path to your command line.

If your custom command line starts a REPL of a project type that is not ”known”/built-in to Calva, use custom as the projectType for the connect sequence.

Custom Command Line Substitutions/Placeholders/Environment variables#

You can use placeholders in your command line, and Calva will substitute them before executing the command. All these placeholders will also be provided to your script via environment variables with the same names (except dashes will be underscores in the env variable names):

nREPL dependency versions:



  • JACK-IN-PROJECT-ROOT-PATH: (See projectRootPath, above)
  • JACK-IN-NREPL-PORT-FILE: The path of the nREPL port file (see nReplPortFile above)

Depending on the project type Calva will also look for these placeholders:

  • JACK-IN-CLJ-MIDDLEWARE: The nREPL middleware to be used for the Clojure REPL
  • JACK-IN-CLJS-MIDDLEWARE: The nREPL middleware to be used for the ClojureScript REPL
  • JACK-IN-LEIN-PROFILES: For Leiningen projects, the profiles selected by the user
  • JACK-IN-LEIN-LAUNCH-ALIAS: For Leiningen projects, the launch alias selected by the user
  • JACK-IN-CLI-ALIASES: For deps.edn projects, the aliases selected by the user
  • JACK-IN-CLJS-LAUNCH-BUILDS: For ClojureScript REPLs that configures builds, the builds selected by the user
  • JACK-IN-NREPL-PORT: For some project types (currently nbb, Babashka and Basilisp) Calva provided the TCP port they should use.

Example Custom Jack-in Command lines#

Start a Babashka REPL via WSL#

Calva has a built-in jack-in sequence for starting a Babashka REPL and connect to it. It works as long as the bb process is on the same host as VS Code/Calva is running. So if you want it to run in WSL, but VS Code is running on your computer you need to start bb slightly differently. These settings in your VS Code settings file will give you a jack-in option that works for this:

  "calva.replConnectSequences": [
        "name": "Bashbabka (WSL)",
        "projectType": "custom",
        "customJackInCommandLine": "bash -c 'bb --nrepl-server JACK-IN-NREPL-PORT'",

If you place it in your user settings you will have access to it from any workspace.

An example/skeleton script#

This script doesn't actually start a REPL, it's provided more for giving you an idea about what it could look like, and as a starting point for your real scripts:

#!/usr/bin/env bb

(require '[clojure.string :as str])

(defn parse-args [args]
  (loop [args args
         parsed {}]
    (if (empty? args)
      (let [[flag value & rest-args] args]
        (case flag
          "--aliases" (recur rest-args (assoc parsed :aliases value))
          "--cider-nrepl-version" (recur rest-args (assoc parsed :cider-nrepl-version value))
          (do (println "Unknown parameter:" flag) (System/exit 1)))))))

(defn process-args [args]
  (let [aliases (str/split (:aliases args) #",")
        cider-nrepl-version (:cider-nrepl-version args)
        project-root-path (System/getenv "JACK_IN_PROJECT_ROOT_PATH")]
    (println "Aliases:")
    (doseq [alias aliases]
      (println alias))
    (println "CIDER nREPL version:" cider-nrepl-version)
    (println "JACK_IN_PROJECT_ROOT_PATH:" project-root-path)))

(def parsed-args (parse-args *command-line-args*))

(when (= *file* (System/getProperty "babashka.file"))
  (process-args parsed-args))

It's written in Babashka to encourage you to write your shell scripts in a civilized language. 😀 See the article Changing my mind: Converting a script from bash to Babashka for a small success-story about this mindset. See also bash2bb.

The script reads JACK-IN-CLJS-LAUNCH-BUILDS and JACK-IN-CIDER-NREPL-VERSION from the command line, and JACK_IN_PROJECT_ROOT_PATH from the environment. It could be configured for use in a custom connect sequence like this:

    "customJackInCommandLine": "../../ --aliases JACK-IN-CLJS-LAUNCH-BUILDS --cider-nrepl-version JACK-IN-CIDER-NREPL-VERSION",

Note how in this case the REPL is started two directories ”down” from the workspace root where the script resides.

Example Sequences#

Whether you just want to speed up your workflow or encode some workflow/mechanics into it, it's often the case that you can create a custom sequence that helps.

Minimal menus with full stack shadow-cljs REPLs#

Minimize the amount of selecting from the Jack-in/Connect menu when working with a full-stack shadow-cljs + deps/lein project:

      "name": "backend + frontend",
      "projectType": "shadow-cljs",
      "cljsType": "shadow-cljs",
      "menuSelections": {
        "cljsLaunchBuilds": [
        "cljsDefaultBuild": ":app"

See shadow-cljs + Clojure with Calva: The basics for how Calva and nREPL work with ClojureScript.


This is the connect sequences used in the Polylith Real World App. The (start) sequence lets you jack-in to the project, and starts the Real World App without any prompts. The (connect) sequence can be used if you prefer to start the REPL manually, and want to connect without prompts.

    "calva.replConnectSequences": [
            "projectType": "deps.edn",
            "afterCLJReplJackInCode": "(require '[dev.server] :reload) (in-ns 'dev.server) (start! 6003)",
            "name": "Polylith RealWorld Server REPL (start)",
            "autoSelectForJackIn": true,
            "projectRootPath": ["."],
            "cljsType": "none",
            "menuSelections": {
                "cljAliases": ["dev", "test"]
            "projectType": "deps.edn",
            "name": "Polylith RealWorld Server REPL (connect)",
            "autoSelectForConnect": true,
            "projectRootPath": ["."],
            "cljsType": "none",
    "calva.autoConnectRepl": true,

The calva.autoConnectRepl, when set to true, makes Calva, at project open, look for the nRepl port file and automatically connect the repl if the file exists. Therefore, you can leave the app running when you close the project in VS Code, and Calva will reconnect when you open the project again. (Alternatively, maybe you just need to reload the VS Code window and not lose the REPL state.)

Minimal menus with full stack deps.edn and Figwheel Main REPLs#

Setting for a full-stack application. It starts the backend server when the CLJ REPL has started. Then proceeds to create a custom CLJS REPL (calling in to the application code for this). And then connects to it.

    "calva.replConnectSequences": [
            "name": "Example Sequence",
            "projectType": "Clojure-CLI",
            "afterCLJReplJackInCode": "(go)",
            "cljsType": {
                "startCode": "(do (require '[cljs-test.main :refer :all])(start-nrepl+fig))",
                "isReadyToStartRegExp": "Prompt will show",
                "connectCode": "(do (use 'cljs-test.main) (cljs-repl))",
                "isConnectedRegExp": "To quit, type: :cljs/quit",
                "printThisLineRegExp": "\\[Figwheel\\] Starting Server at.*"

JUXT Edge#

Here is an example from the JUXT Edge project template. It adds two sequences, one for when only the Clojure REPL should be launched and one for when the customized Edge cljs repl should also be connected. The Edge backend + frontend sequence specifies that the web app should be opened by Calva, making cljs repl connection more stable, and also adds menuSelections to skip the launch aliases prompt.

    "calva.replConnectSequences": [
            "name": "Edge backend only",
            "projectType": "deps.edn"
            "name": "Edge backend + frontend",
            "projectType": "deps.edn",
            "cljsType": {
                "dependsOn": "Figwheel Main",
                "startCode": "(do (require 'dev-extras) (dev-extras/go) (println \"Edge Figwheel Main started\") ((resolve 'dev-extras/cljs-repl)))",
                "isReadyToStartRegExp": "Edge Figwheel Main started",
                "openUrlRegExp": "Website listening on: (?<url>\\S+)",
                "printThisLineRegExp": "\\[Edge\\]",
                "shouldOpenUrl": true,
                "connectCode": "(do (require 'dev-extras) ((resolve 'dev-extras/cljs-repl)))",
                "isConnectedRegExp": "To quit, type: :cljs/quit",
                "buildsRequired": false
            "menuSelections": {
                "cljAliases": [

Plain deps.edn#

A deps.edn sequence that does not promote the ClojureScript repl at all (leaving it a Clojure REPL), and leaves that up to you to do interactively. (Could be useful while you are developing a custom cljs repl.) The example is for when adapting a Figwheel Main repl.

    "calva.replConnectSequences": [
            "name": "Do not promote to cljs",
            "projectType": "deps.edn",
            "cljsType": {
                "dependsOn": "Figwheel Main",
                "connectCode": "\"Don't promote me bro!\"",
                "isConnectedRegExp": "Don't promote me bro!"