Code style

All code in HOOMD-blue follows a consistent style to ensure readability. We provide configuration files for linters (specified below) so that developers can automatically validate and format files.

These tools are configured for use with pre-commit in .pre-commit-config.yaml. You can install pre-commit hooks to validate your code. Checks will run on pull requests. Run checks manually with:

pre-commit run --all-files


Python code in HOOMD-blue should follow PEP8 with the formatting performed by yapf (configuration in setup.cfg). Code should pass all flake8 tests and formatted by yapf.



Python code should be documented with docstrings and added to the Sphinx documentation index in doc/. Docstrings should follow Google style formatting for use in Napoleon, with explicit Sphinx directives where necessary to obtain the proper formatting in the final HTML output.

Simulation operations should unambiguously document what calculations they perform using formal mathematical notation and use a consistent set of symbols and across the whole codebase. HOOMD-blue documentation should follow standard physics and statistical mechanics notation with consistent use of symbols detailed in Notation.

When referencing classes, methods, and properties in documentation, use name to refer to names in the local scope (class method or property, or classes in the same module). For classes outside the module, use the fully qualified name (e.g. numpy.ndarray or

Provide code examples for all classes, methods, properties, etc… as appropriate. To the best extent possible, structure the example so that a majority of users can copy and paste the example into their script and set parameters to values reasonable for a wide range of simulations. Add files with your examples in the Sybil configuration in and Sybil will test them. Document examples in this format so Sybil will parse them:

.. rubric:: Example:

.. code-block:: python

    obj = MyObject(parameters ...)
    ... more example code ...


  • Style is set by clang-format

    • Whitesmith’s indentation style.

    • 100 character line width.

    • Indent only with spaces.

    • 4 spaces per indent level.

    • See .clang-format for the full clang-format configuration.

  • Naming conventions:

    • Namespaces: All lowercase somenamespace

    • Class names: UpperCamelCase

    • Methods: lowerCamelCase

    • Member variables: m_ prefix followed by lowercase with words separated by underscores m_member_variable

    • Constants: all upper-case with words separated by underscores SOME_CONSTANT

    • Functions: lowerCamelCase



Documentation comments should be in Javadoc format and precede the item they document for compatibility with many source code editors. Multi-line documentation comment blocks start with /** and single line ones start with ///.

/** Describe a class
 *  Note the second * above makes this a documentation comment. Some
 *  editors like to add the additional *'s on each line. These may be
 * omitted
class SomeClass
        /// Single line doc comments should have three /'s
        Trigger() { }

        /** This is a brief description of a method

            This is a longer description.

            @param arg This is an argument.
            @returns This describes the return value
        virtual bool method(int arg)
            return false;

        /// This is a member variable
        int m_var;

See Trigger.h for a good example.

Other file types

Use your best judgment and follow existing patterns when styling CMake, restructured text, markdown, and other files. The following general guidelines apply:

  • 100 character line width.

  • 4 spaces per indent level.

  • 4 space indent.

Editor configuration

Visual Studio Code users: Open the provided workspace file (hoomd.code-workspace) which provides configuration settings for these style guidelines.