sbt-assembly 1.0.0


In June of 2011, I started working on sbt-assembly for sbt 0.10, based on Coda Hale's assembly-sbt from sbt 0.7, which in turn was probably inspired by maven-assembly-plugin. After ten years, I'm going to call this one 1.0.0. sbt-assembly 1.0.0 is published to Maven Central.

what does it do?

The plugin creates an über-JAR that can be used for easier deployment. As opposed to the regular JAR file created with packageBin task, an über-JAR is one big JAR file with your code, Scala standard library, and all the extenal dependency files. It's a JAR file that can be executed as:

$ java -jar target/scala-2.13/hello-assembly-0.1.0-SNAPSHOT.jar

Over the years, it has also added various features related to über-JAR such as merge strategy and shading.


In plugins.sbt add:

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "1.0.0")

See below for POM consistency setup.



changes with compatibility implication

  • assembly no longer runs test by default. Running test I think was a vestige from Maven phases, and it doesn't really make sense in sbt. #432 by @eed3si9n
  • Deprecated keys jarName, mergeStrategy etc are removed. Use assemblyJarName, assemblyMergeStrategy instead. #432 by @eed3si9n

ThisBuild / assemblyMergeStrategy

Following my own advice in Plugin Best Practice, I tried to provide the default values for as many settings in globalSettings:

assemblyAppendContentHash assemblyCacheOutput assemblyCacheUnzip
assemblyExcludedJars assemblyMergeStrategy assemblyShadeRules

This mean that those keys can be used as:

ThisBuild / assemblyMergeStrategy := ...
// or
lazy val app = (project in file("app"))
    assemblyMergeStrategy := ...
    // more settings here ...

ThisBuild / assemblyMergeStrategy is shared across all subprojects.

negative time fix

I fixed the "Negative Time" warning in #430. This bug is a reminder that JAR file is basically a ZIP file, which is a hot mess. Internally it uses DOS timestamp, so it stores time at 2 second resolution, and epoch starts from January 1st of 1980.

To make the build reproducible, sbt 1.4.0 started wiping out the timestamps in the JAR files, but it used January 1st of 1970. Until this was fixed in sbt 1.4.8, we have JAR files out in the wild with timestamp set to an invalid timestamp that JDK 11 interprets to UNIX timestamp -3600000, or November 20, 1969 08:00+Z. Because some operating systems are unable to handle timestamps before 1970, JDK 11 then throws an exception "Negative Time." sbt-assembly 1.0.0 will reset these timestamps as January 1st, 2010 instead.

other fixes

  • Fixes "Ignored unknown package option FixedTimestamp" warning on sbt 1.5.x #422 by @xuwei-k
  • Fixes examples on the README to use slash syntax #427 by @nevillelyh

POM consistency setup

If you're behind a corporate firewall, and you want to access Maven Central via Artifactory but with POM consistency check enabled:

In plugins.sbt add:

addPomConsisntentSbtPlugin2021Draft("com.eed3si9n" % "sbt-assembly" % "1.0.0")
def sbtPluginModuleName2021Draft(n: String, sbtV: String): String =
  s"""${n}_sbt${if (sbtV == "1.0") "1" else if (sbtV == "2.0") "2" else sbtV}"""
def sbtPluginExtra2021Draft(m: ModuleID): ModuleID =
def addPomConsisntentSbtPlugin2021Draft(m: ModuleID): Setting[Seq[ModuleID]] =
  libraryDependencies += {
    val sbtV = (pluginCrossBuild / sbtBinaryVersion).value
      .withName(sbtPluginModuleName2021Draft(, sbtV))


According to git shortlog -sn --no-merges, sbt-assembly was brought to you by 68 contributors. Thanks!

Thanks to everyone who's helped improve sbt-assembly using them, reporting bugs, improving our documentation, submitting pull requests and answering Stackoverflow questions.

269 Eugene Yokota (eed3si9n)
45 Kenji Yoshida (xuwei-k)
15 Robert J. Macomber
12 Jeroen ter Voorde
9 Coda Hale
5 Eric Christiansen
5 LolHens
5 Sean Sullivan
5 Wu Xiang
4 Thomas Lockney
3 Ahmed Bhamjee
3 Alex Wilson
3 Roland
3 Sam Halliday
3 Shiva Wu
2 Christopher Hodapp
2 Derek Chen-Becker
2 Eliran Bivas
2 Grigory Pomadchin
2 Mathias Bogaert
2 Pierre Kisters
2 yuval.itzchakov
1 Adrian Bravo
1 Ben Fradet
1 Björn Antonsson
1 Damian
1 David Ignjic
1 dfranetovich
1 Eric Poitras
1 Forest Fang
1 Frank S. Thomas
1 Ian Hummel
1 ipostanogov
1 Jaesang Kim
1 Jeff Hodges
1 Jeffrey Olchovy
1 Johannes Rudolph
1 Jorge Ortiz
1 Joseph Naegele
1 Josh Devins
1 Joshua Gao
1 kellydavid
1 Kewei Shang
1 Kirill A. Korinskiy
1 Krzysztof Ciesielski
1 Lucas Torri
1 Luke Kysow
1 Mal Graty
1 Mark Harrah
1 Martin Mauch
1 nafg
1 Nathan Hamblen
1 Neville Li
1 Onilton Maciel
1 Peter Romov
1 Peter Vlugter
1 Philip Wills
1 romusz
1 Ryan Gross
1 sam
1 Samuel Tardieu
1 Santeri Paavolainen
1 Seth Tisue
1 Stephane Landelle
1 Will Sargent
1 Ólafur Páll Geirsson
1 菅原 浩

Before DMing or emailing me your sbt-assembly questions, please read the issue reporting guideline.

For anyone interested in helping sbt-assembly, feel free to pick up GitHub issues or questions on StackOverflow.

related plugins

For deployment purposes, there are other plugins that you might want to consider.

  • sbt-native-packager creates zip files, Docker images and more without unzipping/re-zipping the JAR files. For many deployment scenarios, this would be the go to.
  • sbt-onejar also creates an über-JAR, but it embeds JAR files directly inside the JAR file.
  • sbt-proguard also creates an über-JAR, and it's able to shrink the size by removing unused classes.
  • sbt-native-image creates a GraalVM native image, as in native executable. For command line apps, this is my current favorite.

I'm not quite sure why sbt-assembly remains to be a relatively popular option. Maybe companies are used to maven-assembly-plugin, so it's convenient for projects like Spark to say either you're using sbt or Maven, use assembly for deployment.