Kind 2

Kind 2 is a multi-engine, parallel, SMT-based automatic model checker for safety properties of Lustre programs.

Kind 2 is a command-line tool. It takes as input a Lustre file annotated with properties to be proven invariant (see Kind 2 Input), and outputs which of the properties are true for all inputs, as well as an input sequence for those properties that are falsified. To ease processing by external tools, Kind 2 can output its results in JSON and XML formats (see JSON / XML Output).

By default Kind 2 runs a process for bounded model checking (BMC), two processes for k-induction (one for a fixed value of k=2, and other for increasing values of k), several processes for invariant generation, a process for IC3QE, and several processes for IC3IA in parallel on all properties simultaneously. It incrementally outputs counterexamples to properties as well as properties proved invariant.

The following command-line options control its operation (run kind2 --help for a full list). See Techniques for configuration examples and more details on each technique.

--enable {BMC|IND|IND2|IC3QE|IC3IA|INVGEN|INVGENOS|...} Select model checking engines

By default, all five model checking engines are run in parallel. Give any combination of --enable BMC, --enable IND, --enable IND2, --enable IC3QE and --enable IC3IA to select which engines to run. The option --enable BMC alone will not be able to prove properties valid, choosing --enable IND and --enable IND2 only (or either of the two alone) will not produce any results. Any other combination is sound (properties claimed to be invariant are indeed invariant) and counterexample-complete (a counterexample will be produced for each property that is not invariant, given enough time and resources).

--timeout <int> (default 0 = none) – Run for the given number of seconds of wall clock time

--smt_solver {Bitwuzla|cvc5|MathSAT|SMTInterpol|Yices|Yices2|Z3} (default Z3) – Select SMT solver

--bitwuzla_bin <file> – Executable for Bitwuzla

--cvc5_bin <file> – Executable for cvc5

--mathsat_bin <file> – Executable for MathSAT 5

--smtinterpol_jar <file> – JAR of SMTInterpol

--yices_bin <file> – Executable for Yices 1 (native input)

--yices2_bin <file> – Executable for Yices 2 (SMT input)

--z3_bin <file> – Executable for Z3

-v Output informational messages

-json Output in JSON format

-xml Output in XML format

Try Kind 2 Online

Visit our web interface to try Kind 2 from your browser.


If you use a Linux or a macOS computer, you can download an executable of the latest version of Kind 2 from here. First make sure though that you have the required software described next.

Required Software

To run Kind 2 the following software must be installed on your computer:

Z3 is the presently recommended SMT solver and the default option. For best results, we recommend using a combination of several solvers. For systems with integer and real variables, we recommend using Z3 as the main solver (--smt_solver Z3) and MathSAT as the interpolating solver (--smt_itp_solver MathSAT). For systems with only machine integers, we recommend using Bitwuzla as the main solver (--smt_solver Bitwuzla), MathSAT as the interpolating solver (--smt_itp_solver MathSAT), and Z3 for performing quantifier elimination (--smt_qe_solver Z3).

VS Code Extension

You can also install our extension for Visual Studio Code which provides support for Kind 2. The extension contains Linux and macOS binaries for Kind 2 and Z3 ready to use. Windows is also supported through WSL2 (see here for more details).


Kind 2 is also available on Docker Hub.

Retrieving / updating the image

Install docker and then run

docker pull kind2/kind2:dev

Docker will retrieve the layers corresponding to the latest version of the Kind 2 repository, develop version. If you are interested in the latest release, run

docker pull kind2/kind2


If you want to update your Kind 2 image to latest one, simply re-run the docker pull command.

Running Kind 2 through docker

To run Kind 2 on a file on your system, it is recommended to mount the folder in which this file is as a volume. In practice, run

docker run -v <absolute_path_to_folder>:/lus kind2/kind2:dev <options> /lus/<your_file>


  • <absolute_path_to_folder> is the absolute path to the folder your file is in,

  • <your_file> is the lustre file you want to run Kind 2 on, and

  • <options> are some Kind 2 options of your choice.


  • the fact that the path to your folder must be absolute is a docker constraint;

  • mount point /lus is arbitrary and does not matter as long as it is consistent with the last argument /lus/<your_file>. To avoid name clashes with folders already present in the container however, it is recommended to use /lus;

  • replace kind2:dev by kind2 if you want to run the latest release of Kind2 instead of the develop version;

  • docker run does not update your local Kind 2 image to the latest one: the appropriate docker pull command does.

Packaging your local version of Kind 2

In the docker directory at the top level of the Kind 2 repository, there is a Dockerfile you can use to build your own Kind 2 image. To do so, just run

docker build -t kind2-local -f ./docker/Dockerfile .

at the root of the repository. kind2-local is given here as an example, feel free to call it whatever you want.

Note that building your own local Kind 2 image does require access to the Internet. This is because of the packages the build process needs to retrieve, as well as for downloading the z3 and cvc5 solvers.

Building and installing

If you prefer, you can build Kind 2 directly from sources, either through the OPAM package manager (recommended) or directly using dune.

Using OPAM

Start by installing OPAM 2.x following the instructions on the website, and make sure OPAM has been initialized by running opam init. If you want to build the development version of Kind 2 that includes the most recent changes, as opposed to the latest release, then run

opam pin add -n kind2

(You can always undo this change later using this command opam unpin kind2).

Otherwise, skip the step above and either run

opam install --update-invariant kind2

if you have OPAM 2.1 or later installed on your system, or run

opam depext kind2
opam install --unlock-base kind2

if you have an older version of OPAM (you can run opam --version to check the version).

This guides the installation of the ZeroMQ C library and any other required external dependencies using the default package manager for your OS (may ask sudo permission). It also builds and installs a compatible version of the OCaml compiler and libraries, and the kind2 binary. Now you can start using kind2.

Other options using OPAM

By default, kind2 will be installed into the bin directory of your current OPAM switch. Run

opam install kind2 --destdir=<DIR>

to install the Kind 2 binary into <DIR>/bin. This will also create directories <DIR>/doc and <DIR>/lib.

In alternative, you can clone, move to its top-level directory, and run

make install

to have OPAM install kind2 and its dependencies.

Note that z3 is available in OPAM so it is possible to install it too with OPAM by running:

opam install z3

Be aware, however, that this takes quite a bit of time (up to 25 minutes).

Direct Installation Using Dune

To build directly from sources you will also need the following software first:

First install this software on your system using your preferred method. Then clone the Kind 2 git repository, move to the top-level directory of the repository, and run

dune build src @install
dune install --sections=bin --prefix <DIR>

to install the Kind 2 binary into <DIR>/bin.

You need a supported SMT solver in your PATH environment variable when running kind2.


With OPAM 2.x you can create a local switch which will install all dependencies automatically.

opam switch create .

Alternatively, you can install all dependencies in your current switch by running:

opam install . --deps-only

For running the unit tests for front end, you can install ounit2 library using opam by running:

opam install ounit2

To run the ounit tests, you can use the following dune command:

dune test


Documentation is available online in HTML or PDF forms.

In order to generate the documentation locally, you need:

For HTML documentation, you additionally need:

For PDF documentation, you additionally need:

If you’re on Debian/Ubuntu, assuming you have Python 3 installed, you can run the following:

sudo apt-get install python3-sphinx latexmk texlive-xetex lmodern
pip3 install sphinx_press_theme

See doc/usr/README.rst for more information.