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Nagini is an automatic verifier for statically typed Python programs, based on the Viper verification infrastructure. Nagini is being developed at the Chair of Programming Methodology at ETH Zurich.

Our CAV 2018 tool paper describing Nagini can be found here, and a more detailed description of its encoding can be found in Marco Eilers' thesis. Also see the Wiki for the documentation of Nagini's specification language.

You can try a (rather slow) online version of Nagini on this website.

For use with the PyCharm IDE, try the Nagini PyCharm plugin.

Dependencies (Ubuntu Linux)

Install Java 11 or newer (64 bit) and Python 3.8 or newer (64 bit) and the required libraries:

sudo apt-get install python3-dev

For usage with Viper's verification condition generation backend Carbon, you will also need to install Boogie (version 2.4.21).

Dependencies (Windows)

  1. Install Java 11 or newer (64 bit) and Python 3.8 or newer (64 bit).
  2. Install either Visual C++ Build Tools 2015 ( or Visual Studio 2015. For the latter, make sure to choose the option "Common Tools for Visual C++ 2015" in the setup (see for an explanation).

Getting Started

  1. Create a virtual environment:

    virtualenv --python=python3 <env>
  2. Activate it:

    source env/bin/activate
  3. Install Nagini:

    pip install nagini

    Alternatively, to get the most up-to-date version, install from source; this will require manually getting and compiling Viper (most likely the most recent development version):

    git clone
    cd nagini
    pip install .

Command Line Usage

To verify a specific file from the nagini directory, run:

nagini [OPTIONS]

The following command line options are available:

                Selects the Viper backend to use for verification.
                Possible options are 'silicon' (for Symbolic Execution) and 'carbon'
                (for Verification Condition Generation based on Boogie).
                Default: 'silicon'.

                Select which functions/methods/classes to verify. Expects a comma-
                separated list of names.

                Enable outputting counterexamples for verification errors (experimental).

                Enable verification of secure information flow. v can be true for ordinary
                non-interference (for sequential programs only), poss for possiblistic
                non-intererence (for concurrent programs) or prob for probabilisitc non-
                interference (for concurrent programs).
                Requires silver-sif-extension to be on the classpath, and silicon-sif-
                extension when used with counterexamples.

                Sets the path of the Z3 executable. Alternatively, the
                'Z3_EXE' environment variable can be set.

                Sets the path of the Boogie executable. Required if the Carbon backend
                is selected. Alternatively, the 'BOOGIE_EXE' environment variable can be

                Sets the path to the required Viper binaries ('silicon.jar' or
                'carbon.jar'). Only the binary for the selected backend is
                required. You can either use the provided binary packages installed
                by default or compile your own from source (see below).
                Expects either a single path or a colon- (Unix) or semicolon-
                (Windows) separated list of paths. Alternatively, the environment
                variables 'SILICONJAR', 'CARBONJAR' or 'VIPERJAR' can be set.

To see all possible command line options, invoke nagini without arguments.

Alternative Viper Versions

To use a more recent or custom version of the Viper infrastructure, follow the instructions here. Look for sbt assembly to find instructions for packaging the required JAR files. Use the parameters mentioned above to instruct Nagini to use your custom Viper version.


  1. On Windows: During the setup, you get an error like Microsoft Visual C++ 14.0 is required. or Unable to fnd vcvarsall.bat:

    Python cannot find the required Visual Studio 2015 C++ installation, make sure you have either installed the Build Tools or checked the "Common Tools" option in your regular VS 2015 installation (see above).

  2. While verifying a file, you get a stack trace ending with something like No matching overloads found:

    The version of Viper you're using does not match your version of Nagini. Try updating both to the newest version.

Build Status

Build Status


Nagini is a static verifier for Python 3, based on the Viper verification infrastructure.







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