KeY 2

KeY 2.6.3 is the latest stable release, released on October 11th, 2017. The versions KeY 2.6.x accompany the second KeY Book. For major new features (like state merging etc.), please checkout the nightly build. KeY 2 differs significantly from the previous KeY 1.6 release. The last KeY 1.6 release is KeY 1.6.5 (released on April 18, 2013) and only provided for legacy reasons. KeY Hoare has its own dedicated download page. In case of questions about KeY please contact:

Download or Start

KeY requires Java version 7 or newer and is tested on Linux, OS X and Microsoft Windows.

Supported Java and JML Features

New Features in 2.x

    • Explicit Heap Model and Dynamic Frames
    • Verification of Recursive Methods
    • Further Enhancend JML Support (Details)
    • Simplified representation of integers
    • GUI improvements (refreshed appearance, improved search, keyboard shortcuts)
    • Counter Example Generation & Test Generation
    • Calculus for Information Flow Reasoning
    • Full support for shift-operations and partially for other binary operators
    • Various bugfixes

KeY-Based Eclipse Projects

Detailed information about the provided Eclipse extensions can be found here. To install KeY 2.6.3 for Eclipse 4.7 Oxygen (other 4.x versions (Luna/Mars/Neon) should work as well)
Update Site Name: KeY Eclipse Extensions
Update Site URL:

Known Issues

If no items are shown in the “Install” wizard, please deselect the checkbox “Group items by category”.

Unstable Development Versions (Nightly Builds)

You can download a current snapshot of the KeY development version below.
Webstart (Nightly Build) Have a look at the section Webstart Problems if you have trouble starting KeY via Webstart.
FatJar Distribution Just download and start via java -jar key*-exe.jar.
Source and Binary Artefacts The classical KeY distribution containing a single jar file with all components, sources and JavaDoc files.
Attention: The nightly builds require JRE/JDK with JavaFX! JavaFX is included in Oracle JRE/JDK until Java 11. For OpenJDK, it depends on your distribution, e.g., for Ubuntu, please install openjfx via sudo apt-get install openjfx;, for Fedora, please install java-1.8.0-openjdk-openjfx. Please note that we provide no support for development versions.

Webstart Problems

These issues are most likely only of concern if you are using webstart for the nighlty builds. If you get an error dialog stating that the execution of the application was blocked due to your Java security settings, you have three options. You can either
    • download and run the binary versions using the links provided above,
    • add the website to the exception list of your Java installation, or
    • import our certificate with which the Jar was signed.

Adding our website to the exception list

First, you have to start the Java Control Panel. This can be accomplished via running javaws -viewer in a terminal. Two windows should open: The “Java Cache Viewer” (close this window) and the Java Control Panel. Click on the “Security” tab in the control panel and choose to edit the site list; then, click on “Add” and enter the URL

Import the KeY certificate

Download the file “KEY.cer” which contains our certificate. Open the Java Control Panel via running javaws -viewer and close the cache viewer. Click on the “Security” tab and choose to manage certificates. Then, click on “import”, change the file filter to “All Files”, navigate to the directory where you stored the KEY.cer file, choose it and press OK.

If the two solutions outlined above should fail for you, please resort to downloading and using the compiled binary version.

Known Problems & Workarounds

Strings “don’t work” in projects with auto-generated stubs

Problem description

When using the (otherwise very practical!) feature of the KeY eclipse plugin which automatically generates stubs (empty methods with default specifications) for included library methods, it might happen that symbolic execution of Java programs gets stuck at a place like str = "foo";, where str is a variable of type String.


Normally, String assignments just work, since this behavior is defined in some files shipped with KeY (JavaRedux). However, when generating stubs (that are included via the “bootclasspath” option), the default behavior is overidden by the dummy behavior, resulting in certain elementary things not working.


The workaround is to replace the content of the file “” in the folder “stubs/java/lang/” with the content of the “” originally shipped with KeY, and to furthermore add a file “String.key in the same directory (click on the links to download current versions of those files as of 2018/01/25). Now, String assignments should work again.

Other Problems

If you encounter problems not described here, please have a look into our “Getting Help” section.