Installing Stainless

General Requirement

  • Java 8 JRE It suffices to have headless OpenJDK JRE 8 (e.g. one that one gets with apt install openjdk-8-jre-headless on Debian/Ubuntu). Make sure that java -version reports a version starting with 1.8, such as openjdk version "1.8 or java version "1.8.

Via Docker

If you have Docker installed, you can run the latest Stainless version with:

$ docker run -v "$PWD:/local" epfllara/stainless:latest /local/test.scala

This will pull down the latest Stainless image from Docker Hub, mount the current directory at /local within the container, and invoke Stainless on test.scala, provided it exists in the current directory. See the previous section for a sample test.scala.

Usage With Sbt

Stainless is also avaiable as a sbt plugin, which hooks into the build process to verify your code on compilation. This allows for both verifying your code, compiling, and running your code in one swift motion.

Moreover, thanks to Metals, Stainless diagnostics will automatically appear in your editor of choice (we recommend VS Code), while the full log will typically be available in a separate window/pane. To this end, please follow the installation instructions for your editor on the Metals website.

To ease the process, we provide a template for a Stainless-enabled sbt project which one can then import into their editor of choice to get started in a few steps: Sbt Template Project

Alternatively, one can also integrate Stainless into an existing sbt project: Usage Within An Existing Project.

Sbt Template Project

Install sbt:

Follow the instructions at to install sbt 1.3.0.

Create a new project from the template:

  1. In a console, create a new project with the following command:

    sbt new epfl-lara/stainless-project.g8
  2. Fill in a name for your project, eg. My Great Project.

  3. Leave the proposed Stainless version as is, ie, just press ENTER.

  4. sbt will now create a project under ./my-great-project.

  5. Put the source files you want to verify under verified/src/main/scala/ and your regular Scala code under core/src/main/scala/.

  6. Launch sbt and, at its prompt, type the following command:

    > core/run

    This will compile, verify, and run your code!

  7. To only compile and verify your code, you can use the following command:

    > verified/run

Usage Within An Existing Project

Stainless can also be used within an existing sbt 1.3.0 project.

  1. Start by installing an external solver (see Section “External Solver Binaries”).

  2. Add the sbt-stainless plugin together with the required resolver to your project/plugins.sbt

resolvers ++= Seq(
  Resolver.bintrayRepo("epfl-lara", "princess"),
  Resolver.bintrayIvyRepo("epfl-lara", "sbt-plugins"),
  ("uuverifiers" at "").withAllowInsecureProtocol(true),

addSbtPlugin("ch.epfl.lara" % "sbt-stainless" % "<insert-version>")

Check the GitHub releases or the sbt-stainless bintray repository for the available versions.

  1. In your project’s build file, enable the StainlessPlugin on the modules that should be verified by Stainless. Below is an example:

// build.sbt
lazy val algorithm = project
  .enablePlugins(StainlessPlugin) // <-- Enabling Stainless verification on this module!

Note that if you are using .scala build files you need to use the fully qualified name ch.epfl.lara.sbt.stainless.StainlessPlugin. Also, because stainless accepts a subset of the Scala language, you may need to refactor your build a bit and code to successfully use Stainless on a module.

  1. After modifying the build, type reload if inside the sbt interactive shell. From now on, when executing compile on a module where the StainlessPlugin is enabled, Stainless will check your Scala code and report errors in the shell (just like any other error that would be reported during compilation).

That’s all there is to it. However, the sbt-stainless plugin is a more recent addition to Stainless compared to command-line script. It has seen less testing in the field and currently has the following limitations:

  • No incremental compilation support. All sources (included the stainless-library sources) are recompiled at every compile execution.ub

  • The plugin does not support Scala 3 (dotty). To track sbt support in dotty you can follow issue #178.

Also, note that the plugin offers a stainlessEnabled setting that can help experimenting with Stainless. The stainlessEnabled setting is set to true by default, but you can flip the flag to false by typing set every stainlessEnabled := false while inside the sbt interactive shell.

  1. It is possible to specify extra source dependencies to be added to the set of files processed by Stainless via the stainlessExtraDeps setting. For example, to add both the stainless-algebra and stainless-actors packages, along with the latter’s dependency on Akka, one can add the following settings to their build:

stainlessExtraDeps ++= Seq(
  "ch.epfl.lara" %% "stainless-algebra" % "0.1.2",
  "ch.epfl.lara" %% "stainless-actors"  % "0.1.1",

libraryDependencies += "com.typesafe.akka" %% "akka-actor" % "2.5.21"

Note that the dependencies specified in stainlessExtraDeps must be available as a source JAR from any of the resolvers configured in the build.

External Solver Binaries

If no external SMT solvers (such as Z3 or CVC4) are found, Stainless will use the bundled Scala-based Princess solver

To improve performance, we highly recommend that you install the following two additional external SMT solvers as binaries for your platform:

You can enable these solvers using --solvers=smt-z3 and --solvers=smt-cvc4 flags.

Solver binaries that you install should match your operating system and your architecture. We recommend that you install these solvers as a binary and have their binaries available in the $PATH (as z3 or cvc4).

Note that somewhat lower version numbers of solvers should work as well and might even have different sets of soundness-related issues.

You can use multiple solvers in portfolio mode, as with the options --timeout=15 --solvers=smt-z3,smt-cvc4, where verification succeeds if at least one of the solvers proves (within the given number of seconds) each the verification conditions. We suggest to order the solvers starting from the one most likely to succeed quickly.

For final verification runs of highly critical software, we recommend that (instead of the portfolio mode) you obtain several solvers and their versions, then try a single solver at a time and ensure that each verification run succeeds (thus applying N-version programming to SMT solver implementations).

Install Z3 4.8.6 (Linux & macOS)

  1. Download Z3 4.8.6 from

  2. Unzip the downloaded archive

  3. Copy the z3 binary found in the bin/ directory of the inflated archive to a directory in your $PATH, eg., /usr/local/bin.

  4. Make sure z3 can be found, by opening a new terminal window and typing:

$ z3 --version
  1. The output should read:

Z3 version 4.8.6 - 64 bit`

Install CVC 1.7 (Linux)

  1. Download CVC4 1.7 from (reachable from )

  2. Copy or link the downloaded binary under name cvc4 to a directory in your $PATH, eg., /usr/local/bin.

  1. Make sure cvc4 can be found, by opening a new terminal window and typing:

$ cvc4 --version | head
  1. The output should begin with:

This is CVC4 version 1.7

Install CVC 1.6 (macOS)

  1. Install Homebrew

  2. Install CVC4 using the Homebrew tap at

  3. Make sure cvc4 can be found, by opening a new terminal window and typing:

$ cvc4 --version
  1. The output should begin with:

This is CVC4 version 1.6

Build from Source on Linux & macOS

To build Stainless, we use sbt. In a typical configuration, sbt universal:stage in the root of the source tree should work, yet, in an attempt to be more reproducible and independent from sbt cache and path, the instructions below assume that the directory called stainless does not exist, they instruct sbt to use a relative path for its bootstrap, and do not require adding sbt to your path.

Install sbt

Follow the instructions at to install sbt 1.3.0.

Check out sources

Get the sources of Stainless by cloning the official Stainless repository:

$ git clone
Cloning into 'stainless'...

Run sbt

The following instructions will invoke sbt while using a stainless sub-directory to download files.

$ cd stainless
$ sbt universal:stage

Where to find generated files

The compilation will automatically generate the following two bash scripts:

  1. frontends/scalac/target/universal/stage/bin/stainless-scalac that will use the scalac compiler as frontend,

  2. frontends/stainless-dotty/target/universal/stage/bin/stainless-dotty that uses the dotc compiler as frontend (experimental).

You may want to introduce a soft-link from frontends/scalac/target/universal/stage/bin/stainless-scalac to a file called stainless:

$ ln -s frontends/scalac/target/universal/stage/bin/stainless-scalac stainless

Analogous scripts work for various platforms and allow additional control over the execution, such as passing JVM arguments or system properties:

$ frontends/scalac/target/universal/stage/bin/stainless-scalac -Dscalaz3.debug.load=true -J-Xmx6G --help

Note that Stainless is organized as a structure of several projects. The main project lives in core while the two available frontends can be found in frontends/scalac and frontends/dotty. From a user point of view, this should most of the time be transparent and the build command should take care of everything.

Build from Source on Windows 10

Before following the infrequently updated instructions in this section, considering running Ubuntu on Windows 10 and following the instructions for Linux. That said, Stainless is just a JVM application that invokes binaries that are also available for Windows, so it is not too difficult to build a version that runs without a VM.

Get the sources of Stainless by cloning the official Stainless repository. You will need a Git shell for windows, e.g. Git for Windows.

$ git clone
Cloning into 'stainless'...
// ...
$ cd stainless
$ sbt clean universal:stage
// takes about 1 minutes

Compilation will automatically generate the following two bash scripts:

  1. frontends/scalac/target/universal/stage/bin/stainless-scalac.bat that will use the scalac compiler as frontend,

  2. frontends/stainless-dotty/target/universal/stage/bin/stainless-dotty.bat that uses the dotc compiler as frontend (experimental).

Running Tests

Stainless comes with a test suite. Use the following commands to invoke different test suites:

$ sbt test
$ sbt it:test

It’s also possible to run tests in isolation, for example, the following command runs Extraction tests on all files in termination/looping:

$ sbt 'it:testOnly *ExtractionSuite* -- -z "in termination/looping"'

Building Stainless Documentation

Stainless documentation is available at . To build the documentation locally, you will need Sphinx ( ), a restructured text toolkit that was originally developed to support Python documentation.

  • On Ubuntu 18, you can use sudo apt install sphinx-common

The documentation resides in the core/src/sphinx/ directory and can be built using the provided Makefile. To do this, in a Linux shell, type make html, and open in your web browser the generated top-level local HTML file, by default stored in src/sphinx/_build/html/index.html. Also, you can open the *.rst documentation files in a text editor, as they are human-readable in their source form as well.