The Chemistry Development Kit

bioinformatics, cheminformatics, chemistry, code4lib, java


Build Status Maven Central

The Chemistry Development Kit (CDK)

Copyright 1997-2018 The CDK Development Team

License: LGPL v2, see doc/lgpl.license


You are currently reading the README file for the Chemistry Development Project (CDK). This project is hosted under Please refer to these pages for updated information and the latest version of the CDK. CDK's API documentation is available though our Github site.

The CDK is an open-source library of algorithms for structural chemo- and bioinformatics, implemented in the programming language Java(tm). The library is published under terms of the the GNU Lesser General Public License v2. This has implications on what you can do with sources and binaries of the CDK library. For details, please refer to the file LICENSE, which should have been provided with this distribution.

PLEASE NOTE: This is a library of useful data structures and algorithms to manipulate them from the area of structural chemo- and bioinformatics. As such, it is intended for the use by programmers, who wish to save some effort by reusing code. It is not intended for the enduser. If you consider yourself to be more like user, you might not find what you wanted. Please refer to other projects like the JChemPaint project ( or the Jmol project ( for programs that actually take advantage of the CDK library.


Compiling the library is performed with Apache Maven and currently requires Java 1.7 or later. From the root of the project run:

$ git clone
$ cd cdk/
$ mvn package -DskipTests # run the tests if you like!

This will produce a 'jar' file for each module located in each modules 'target/' directory. The uber jar with everything included is located in cdk/bundle/target/cdk-<version>.jar.

Creating the JavaDoc

The JavaDoc documentation for the API describes all of the CDK classes in detail. It functions as the user manual for the CDK, although you should also look at the list of examples and tutorials below.

Before creating the JavaDoc you will need to install the CDK build util project in your local maven repo.

git clone
cd cdk-build-util
mvn install

The documentation on the main project can then be created:

cdk/$ ls pom.xml
cdk/$ mvn javadoc:aggregate

The documentation is created as a series of .html pages in target/site/apidocs. If you use firefox, you can read the documentation using the following command:

cdk/$ firefox target/site/apidocs/index.html

Creating a Jar of all sources

To create a Jar containing all source files use the following command on the main pom.

cdk/$ mvn source:aggregate

The cdk-{version}-sources.jar will be generated in the target/directory.

Running tests

IMPORTANT: this requires the Git version of the sources, because the test files are not included in the source code distribution.

After you compiled the code, you can do "mvn test" to run the test suite of non-interactive, automated tests. Upon "mvn test", you should see something like:

Tests run: 199, Failures: 0, Errors: 0, Skipped: 0

As you can see, the vast majority of tests ran successfully, but that there are failures and errors.

You can run the tests for an individual module by changing to the module directory:

cdk/$ cd descriptor/fingerprint
cdk/descriptor/fingerprint/$ mvn test

Tutorials on building the project in integrated development environments (IDEs) are available on the wiki:

Using CDK

CDK is a class library intended to be used by other programs. It will not run as a stand-alone program, although it contains some GUI- and command line applications. If your project is also using maven you can install the library in your local repository (~/.m2/repository) as follows:

cdk/$ mvn install -Dmaven.test.failure.ignore=true

A large bundled jar with all dependencies can also be built. If you have locally made modifications to the source code you will need to install these to your local repository. The jar will in the target directory of the 'bundle' module.

cdk/$ mvn install -DskipTests=true
cdk/$ ls bundle/target/cdk-{version}.jar

If you have not made any changes you need only package the bundle module. The other modules will be automatically downloaded.

cdk/$ cd bundle
cdk/$ mvn package
cdk/$ ls target/cdk-{version}.jar

Maven Artefacts

Maven artefacts of each module are deployed to the Maven Central Repository. To use a CDK module just specify the dependency in your pom.xml. Any additional requirements of the module will also be downloaded and included.


To include everything in the library use the cdk-bundle artefact.

Maven reporting plugins

This section details how to run the plugins and access the reports.


PMD analyses code style (e.g. variable naming, complexity) and reports potential bugs. Currently only production (non-test) code is inspected. The following snippet shows how to run PMD on the 'cdk-silent' module.

cdk/: cd base/silent
cdk/base/silent: ls
cdk/base/silent: mvn pmd:pmd
cdk/base/silent: open target/site/pmd.html 


As a relatively mature project with many different developers there are many different formatting styles used in the CDK source code. Following patches from different IDEs with different settings some files have gotten pretty messy. The java-formatter tidies up the code using consistent settings.

The formatting settings are in the cdk-build-util project cdk-build-util/.../cdk-formatting-conventions.xml.

To run the formatter on the silent module

cdk/: cd base/silent
cdk/base/silent: ls
cdk/base/silent: mvn java-formatter:format
[INFO] --- maven-java-formatter-plugin:0.4:format (default-cli) @ cdk-silent ---
[INFO] Using 'UTF-8' encoding to format source files.
[INFO] Number of files to be formatted: 76
[INFO] Successfully formatted: 76 file(s)
[INFO] Fail to format        : 0 file(s)
[INFO] Skipped               : 0 file(s)
[INFO] Approximate time taken: 3s


JaCoCo is a tool for analysing test coverage. JaCoCo installs agent instrumentation and check exactly which code lines are hit and missed by tests. This not only serves as a quality measure but also can guide optimisation, "why isn't that conditional ever hit by my tests, is it even possible?".

cdk/: cd base/silent
cdk/base/silent: mvn jacoco:prepare-agent test jacoco:report
cdk/base/silent: open target/site/jacoco/index.html

The contribute method determines the number of pi electrons for an element with specified valence (v) and connectivity (x). We can see that two lines are flagged as yellow. On inspection we can see that 1 of 4 branches was missed. There are four branches because of two conditionals (2^2=4) and one of them is missed.

You can run single tests as follows:

cdk/base/silent: mvn jacoco:prepare-agent test jacoco:report -Dtest=AtomContainerTest

Some IDEs and CI servers are able to integrate the JaCoCo reports directly.

Reporting coverage when the tests are separate to the production code is a little more tricky but possible. Here is an example for the 'cdk-standard' module.

cdk/: cd base/standard
cdk/base/standard: mvn install
cdk/base/standard: cd ../test-standard
cdk/base/test-standard: mvn jacoco:prepare-agent test
cdk/base/standard: cd ../standard
cdk/base/standard: mvn jacoco:report
cdk/base/standard: open target/site/jacoco/index.html

Dependency Tree

Maven can create a dependency tree with the following command:

cdk/: mvn dependency:tree

Examples and tutorials

To get started using the CDK, you may be interested in the following websites which contain examples and tutorials:

To keep up with the latest news on CDK development and usage


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