Checkstyle

Checkstyle^[1] is a static code analysis tool used in software development for checking if Java source code is compliant with specified coding rules.

Checkstyle
Stable release	12.1.2 / November 11, 2025; 10 days ago (2025-11-11)
Repository	github.com/checkstyle/checkstyle
Written in	Java
Operating system	Cross-platform
Type	Static code analysis
License	GNU Lesser General Public License
Website	checkstyle.sourceforge.net

Originally developed by Oliver Burn back in 2001, the project is maintained by a team of developers from around the world.

The current stable release is version 12.1.2^[2] which supports Java versions from 17.^[3]

Advantages and limits

The programming style adopted by a software development project can help to ensure that the code is compliant with good programming practices which improve the quality, readability, and re-usability of the code and may reduce the cost of development. The checks performed by Checkstyle are mainly limited to the presentation of the code. These checks do not confirm the correctness or completeness of the code. Checkstyle rules are not programming style, they are merely rules for formatting the code.

Examples of available modules

Checkstyle defines a set of available modules, each of which provides rules checking with a configurable level of strictness (mandatory, optional...). Each rule can raise notifications, warnings, and errors. For example, Checkstyle can examine the following:

• Javadoc comments for classes, attributes and methods;
• Naming conventions of attributes and methods;
• The number of function parameters;
• Line lengths;
• The presence of mandatory headers;
• The use of imports, and scope modifiers;
• The spaces between some characters;
• The practices of class construction;
• Multiple complexity measurements.

Usage

Checkstyle is available as a JAR file which can run inside a Java VM or as an Apache Ant task. It can also be integrated into an IDE or other tools.

History and development

Checkstyle was created and first released in 2001 by developer Oliver Burn as an open-source tool to automate the enforcement of Java coding standards.^[4] Version 1.1, the earliest publicly available release, was published in June 2001.^[5] Initially a solo project, Checkstyle began attracting outside contributors by 2003, with additional developers participating in version 3.0 and beyond.^[6] Burn continued to lead development for over a decade before development shifted to other lead developers by 2015.^[7]

Checkstyle was designed to verify source code compliance with standard coding conventions, such as those defined by Sun Microsystems for Java.^[8] Early project documentation described its purpose as automating style checks to “spare humans of this boring (but important) task” and to reduce debates over coding style during reviews. Checkstyle’s inspections focused on syntactic and stylistic conventions—such as Javadoc completeness, naming patterns, required braces, whitespace usage, and maximum line lengths—rather than program semantics or defect detection. Its documentation emphasized that it was not a code formatter, a replacement for a coding standard, or a substitute for full code reviews, but rather a tool intended to complement existing development and quality-assurance practices.^[9]

At the time of Checkstyle’s release, Java developers had limited tooling options for automated code analysis. One of the earliest commercial offerings was Jtest by Parasoft, introduced in 1997, which combined automated unit test generation with static analysis techniques that simulated code execution to identify potential runtime defects—often across multiple methods or classes.^[10] However, Jtest did not focus on enforcing coding style or formatting conventions—leaving room for dedicated style-oriented tools such as Checkstyle. In the open-source ecosystem, Ralph Jocham’s Java Coding Standard Checker (JCSC) provided similar functionality focused on style enforcement, receiving updates through the Java 1.5 era but showing no substantial development activity after 2005.^[11]

Shortly after Checkstyle's appearance, several complementary tools emerged. PMD, released in 2002, identified common programming flaws and anti-patterns by scanning Java source code. FindBugs, launched in 2006 as a project of the University of Maryland, performed analysis on compiled Java bytecode to uncover likely defects.^[12] Around the same time, JLint offered static checks focused on concurrency issues and basic semantic inconsistencies.^[13] Contemporary comparisons published by other tool maintainers, such as PMD's “similar projects” index, grouped Checkstyle alongside these tools as part of the broader Java static-analysis ecosystem.^[14]

Checkstyle stood out in this evolving landscape by concentrating exclusively on style and structural conventions. As a result, it became a popular addition to Java development toolchains, often used in tandem with build systems such as Apache Ant and Maven, as well as in continuous integration pipelines and academic environments.

See also

• Free and open-source software portal

• List of tools for static code analysis
• EclipseCS - Eclipse plugin for checkstyle.
• Checkstyle-IDEA - Checkstyle plugin for IntelliJ IDEA and Android Studio
• SevNTU-Checkstyle Archived 2013-03-22 at the Wayback Machine - extension for EclipseCS with number of check that are not part of checkstyle upstream.
• Checkstyle Addons - Additional Checkstyle checks
• Checkstyle for PHP - a PHP version of Checkstyle