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An SBT plugin for dangerously fast development turnaround in Scala
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Latest commit a62a9fa @jrudolph jrudolph Reorder README a bit

sbt-revolver is a plugin for SBT enabling a super-fast development turnaround for your Scala applications.

It sports the following features:

  • Starting and stopping your application in the background of your interactive SBT shell (in a forked JVM)
  • Triggered restart: automatically restart your application as soon as some of its sources have been changed

Even though sbt-revolver works great with spray on spray-can there is nothing spray-specific to it. It can be used with any Scala application as long as there is some object with a main method.


sbt-revolver requires SBT 0.13.x or greater. Add the following dependency to your project/plugins.sbt:

addSbtPlugin("io.spray" % "sbt-revolver" % "0.8.0")

sbt-revolver is an auto plugin, so you don't need any additional configuration in your build.sbt nor in Build.scala to make it work. In multi-module builds it will be enabled for each module.

For older versions of sbt see version 0.7.2.


sbt-revolver defines three new commands (SBT tasks) in its own re configuration:

  • re-start <args> --- <jvmArgs> starts your application in a forked JVM. The optionally specified (JVM) arguments are appended to the ones configured via the re-start-args/ java-options(for re-start) setting (see the "Configuration" section below). If the application is already running it is first stopped before being restarted.

  • re-stop stops application. This is done by simply force-killing the forked JVM. Note, that this means that shutdown hooks are not run (see #20).

  • re-status shows an informational message about the current running state of the application.

Triggered Restart

You can use ~re-start to go into "triggered restart" mode. Your application starts up and SBT watches for changes in your source (or resource) files. If a change is detected SBT recompiles the required classes and sbt-revolver automatically restarts your application. When you press <ENTER> SBT leaves "triggered restart" and returns to the normal prompt keeping your application running.


The following SBT settings defined by sbt-revolver are of potential interest:

  • re-start-args, a SettingKey[Seq[String]], which lets you define arguments that sbt-revolver should pass to your application on every start. Any arguments given to the re-start task directly will be appended to this setting.
  • re-start::re-main-class, which lets you optionally define a main class to run in re-start independently of the one set for running the project normally. This value defaults to the value of compile:main-class(for run). If you don't specify a value here explicitly the same logic as for the normal run main class applies: If only one main class is found it one is chosen. Otherwise, the main-class chooser is shown to the user.
  • re-start::java-options, a SettingKey[Seq[String]], which lets you define the options to pass to the forked JVM when starting your application
  • re-start::base-directory, a SettingKey[File], which lets you customize the base directory independently from what run assumes.
  • re-start::full-classpath, which lets you customize the full classpath path for running with re-start.
  • re-jrebel-jar, a SettingKey[String], which lets you override the value of the JREBEL_PATH env variable.
  • re-colors, a SettingKey[Seq[String]], which lets you change colors used to tag output from running processes. There are some pre-defined color schemes, see the example section below.
  • re-log-tag, a SettingKey[String], which lets you change the log tag shown in front of log messages. Default is the project name.
  • debug-settings, a SettingKey[Option[DebugSettings]] to specify remote debugger settings. There's a convenience helper Revolver.enableDebugging to simplify to enable debugging (see examples).


To configure a 2 GB memory limit for your app when started with re-start:

javaOptions in Revolver.reStart += "-Xmx2g"

To set a special main class for your app when started with re-start:

mainClass in Revolver.reStart := Some("com.example.Main")

To set fixed start arguments (than you can still append to with the re-start task):

Revolver.reStartArgs := Seq("-x")

To enable debugging with the specified options:

Revolver.enableDebugging(port = 5050, suspend = true)

To change set of colors used to tag output from multiple processes:

Revolver.reColors := Seq("blue", "green", "magenta")

There are predefined color schemes to use with reColors: Revolver.noColors, Revolver.basicColors, Revolver.basicColorsAndUnderlined.

Hot Reloading

Note: JRebel support in sbt-revolver is not actively supported any more.

If you have JRebel installed you can let sbt-revolver know where to find the jrebel.jar. You can do this either via the Revolver.jRebelJar setting directly in your SBT config or via a shell environment variable with the name JREBEL_PATH (which is the recommended way, since it doesn't pollute your SBT config with system-specific settings). For example, on OSX you would add the following line to your shell startup script:

export JREBEL_PATH=/Applications/ZeroTurnaround/JRebel/jrebel.jar

With JRebel sbt-revolver supports hot reloading:

  • Start your application with re-start.
  • Enter "triggered compilation" with ~products. SBT watches for changes in your source (and resource) files. If a change is detected SBT recompiles the required classes and JRebel loads these classes right into your running application. Since your application is not restarted the time required to bring changes online is minimal (see the "Understanding JRebel" section below for more details). When you press <ENTER> SBT leaves triggered compilation and returns to the normal prompt keeping your application running.
  • If you changed your application in a way that requires a full restart (see below) press <ENTER> to leave triggered compilation and re-start.
  • Of course you always stop the application with re-stop.


sbt-revolver is licensed under APL 2.0.

Patch Policy

Feedback and contributions to the project, no matter what kind, are always very welcome. However, patches can only be accepted from their original author. Along with any patches, please state that the patch is your original work and that you license the work to the sbt-revolver project under the project’s open source license.

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