KeY is a deductive verification system for Java programs

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What KeY can do for you

KeY -- Deductive Java Program Verifier

Tests CodeQL CodeQuality

This repository contains the interactive theorem prover "KeY" for the verification of Java programs.

You can find more information about KeY on or use the documentation in the companion repository key-docs. The content of the latter is also available as HTML version under

The current version of KeY is 2.10.0, licensed under GPL v2.


  • Hardware: >=2 GB RAM
  • Operating System: Linux/Unix, MacOSX, Windows
  • Java SE 8 or newer
  • Optionally, KeY can make use of the following binaries:

Content of the KeY folder

This folder provides a gradle-managed project following Maven's standard folder layout. There are several subprojects in this folder. In general, every key.*/ subproject contains a core component of KeY. Additional and optional components are in keyext.*/ folders. The file build.gradle is the root build script describing the dependencies and common build tasks for all subprojects.

key.util, key.core and key.ui are the base for the product "KeY Prover". Special care is needed if you plan to make changes here.

Compile and Run KeY

Assuming you are in the directory of this README file, you can create a runnable and deployable version with one of these commands:

  1. With ./gradlew key.ui:run you can run the user interface of KeY directly from the repository. Use ./gradlew key.ui:run --args='--experimantal' to enable experimental features.

  2. Use ./gradlew classes to compile KeY, which includes running JavaCC and Antlr. Likewise, use ./gradlew testClasses if you also want to compile the JUnit test classes.

  3. Test your installation with ./gradlew test. Be aware that this will usually take multiple hours to complete. With ./gradlew testFast, you can run a more lightweight test suite that should complete in a few minutes.

    You can select a specific test case with the --tests argument. Wildcards are allowed.

    ./gradlew :key.<subproject>:test --tests "<class>.<method>"

    You can debug KeY by adding the --debug-jvm option, then attaching a debugger at localhost:5005.

  4. You can create a single jar-version, aka fat jar, of KeY with

    ./gradlew :key.ui:shadowJar

    The file is generated in key.ui/build/libs/key-*-exe.jar.

  5. A distribution is build with

    ./gradlew :key.ui:installDist :key.ui:distZip

    The distribution can be tested by calling key.ui/install/key/bin/key.ui and is zipped in key.ui/build/distributions.

    The distribution gives you potential of using single jar files.

Developing KeY

  • Quality is automatically assessed using SonarQube on each merge requests. The results of the assessments can be found on (Branches).

    The rules and quality gate are maintained by Alexander Weigl currently.

  • More guideline and documentation for the KeY development can be found under key-docs.

Issues and Bug Reports

If you encounter problems, please send a message to


License Remark

This is the KeY project - Integrated Deductive Software Design
Copyright (C) 2001-2011 Universität Karlsruhe, Germany
						Universität Koblenz-Landau, Germany
						and Chalmers University of Technology, Sweden
Copyright (C) 2011-2022 Karlsruhe Institute of Technology, Germany
						Technical University Darmstadt, Germany
						Chalmers University of Technology, Sweden

The KeY system is protected by the GNU General Public License.
See LICENSE.TXT for details.
Logo of KeY
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Programming languages
  • Java 98%
  • HTML 1%
  • Other 1%
  • GPL-2.0-only
</>Source code

Participating organisations

Karlsruhe Institute of Technology (KIT)
University of Koblenz and Landau
Chalmers University of Technology
Technical University of Darmstadt