Thanks for your interest in contributing to this project! This project is free open source and as such dependent on your contributions. These guidelines should help you get started more quickly and should ensure a smooth contribution process for both those contributing and those reviewing contributions. Please read them thoroughly before contributing with a Pull Request, and at least skim them before adding an issue.

How to ask for help

At the moment, it is totally fine to open an issue if you have any questions. This might change though, depending on the time needed to answer. Although, please note that this is free and open source software and there are no guarantees on any kind of support from our side.

How to report a bug or request a feature

When submitting a bug report please use clear details about the issue you’re facing, any additional dependencies you have, include the stacktrace if possible and any other details that would help us reproduce the issue.

If you’re asking for a new feature, try to describe your use case and how to do think this feature would benefit yourself and/or others. Given that this repo is a free open source project, chances of your idea coming into fruition are much higher if you are also willing to contribute a PR. Please first open the issue, though, so we can discuss the feature before you have to spend time on it.

How to create a PR


Any contributions you make will be under the MIT Software License. In short, when you submit code changes, your submissions are understood to be under the same LICENCE that covers the project. Feel free to contact the maintainers if that’s a concern.


We strongly recommend to first open an issue discussing the contribution before creating a PR, unless you are really sure that the contribution does not need discussion (e.g. fixing a typo in documentation).

Please note that we can only merge a PR if:

  • The code is following the official kotlin codestyle as defined by Jetbrains.

  • All tests pass, and the code has 100% test coverage (run ./gradlew clean test to run the checks). If it does not make sense to cover a certain line of code, please mention that in the PR.

  • Bigger changes and new features are also covered by integration test(s) which can be run with gradle integrationTest task.

  • All relevant documentation is updated. Usually this means updating the KDoc of the code you work on, README and documentation in docs dir.

  • Additional third-party dependencies are only added with a good reason.

  • Code was reviewed by one of the regular contributors, taking into consideration code readability, security and whether the addition aligns with the long-term roadmap.

Set up instructions

First please fork this repository to be able to contribute any changes.

The code in this codebase is managed by Git for version control, and it uses Gradle as a build tool. We use gradle wrapper, so you normally don’t need to install gradle separately.

You can run ./gradlew clean test to download the dependencies and ensure that everything is set up correctly.

Now you can create a new branch describing the change you are about to make, e.g. fix_typo_in_documentation, and start coding.

Your First Contribution

If you are interested in contributing, but don’t have a specific issue at heart, we would recommend looking through the issues labelled help wanted.

If you are new to contributing to open source, we recommend having a look at a free tutorial for this. Issues labelled good first issue are meant specifically to get started in the repository.

If you are stuck at any point, feel free to comment in the issue you chose. We try to be as helpful to newcomers as possible, and you don’t have to be afraid of "dumb" questions.

If this is your first pull request - please add yourself to the "contributors section" in data.yml file so that you get proper credit in the project’s About page.

Code Structure

This repository consists of the following modules:

Adding new functionality

This section describes how to add new functionality to kotlin-faker.


Most of the data generated by kotlin-faker comes from .yml "dictionary" files located in locales directory.

A data provider class - e.g. Address - represents a certain "category" of fake data - in this case data related to address information.

Kotlin-faker also generates data in various locales, en being the default one. The locales/en directory contains .yml files for all existing data providers, usually one file per provider, while localized dictionaries usually contain all the data in a single file, e.g. locales/uk.yml.

Adding a new Data Provider

Adding a new data provider is usually a straightforward process, as most of the "heavy lifting" does not change from one provider to another. It does involve changes in several places though, which are explained in this section.

Add a new .yml file to locales/en

Let’s take the name.yml file for the Name provider, as an example:

# core/src/main/resources/locales/en/name.yml
      male_first_name: [Aaron, Abdul, Abe]
      female_first_name: [Abbey, Abbie, Abby]
  • en is the locale name (in the case of a new data provider it’s always going to be en as it’s the default one)

  • name is the data category name

  • male_first_name and female_first_name are functions inside the Name class which generates random data.

For more details and examples take a look at some of existing .yml files.

Create the new data provider class under provider directory.

The class needs to implement YamlFakeDataProvider, and override a few properties. Expanding on the same data provider example, let’s look at the Name class implementation:

class Name internal constructor(fakerService: FakerService) : AbstractFakeDataProvider<Name>(fakerService) {
    override val yamlCategory = YamlCategory.NAME
    override val localUniqueDataProvider = LocalUniqueDataProvider<Name>()
    override val unique by UniqueProviderDelegate(localUniqueDataProvider)

    init {

    fun maleFirstName() = resolve("male_first_name")
    fun femaleFirstName() = resolve("female_first_name")
  • the category property that uses the YamlCategory.NAME enum class, which has to be the same as declared in the .yml file. If the enum category does not already exist (Some dictionary files use the same category, which is perfectly fine to do if it makes sense) - new one should be added as well.

  • the YamlFakeDataProvider provides a resolve function that should be used to get the random value for a given category key, i.e. female_first_name.

Add the property to Faker class

  • the entry point for all data generation is the Faker class, so a new property needs to be added there that calls the data provider class

Update native-image reflect-config.json

  • this is used when building the native-image of the faker-bot CLI application and thus needs to be updated, otherwise the nativeImage gradle task will fail

  • it is easy to auto-update the configuration by using native-image-agent (requires the native-image binary to be installed):

    • first create the jar of the app with ./gradlew clean shadowJar

    • then run each of the cli commands (include the verbose mode since that requires additional calls):

      • java -agentlib:native-image-agent=config-merge-dir=temp_resources -jar cli-bot/build/libs/cli-bot-1.11.1-SNAPSHOT-fat.jar list --verbose

      • java -agentlib:native-image-agent=config-merge-dir=temp_resources -jar cli-bot/build/libs/cli-bot-1.11.1-SNAPSHOT-fat.jar lookup name --verbose

    • then copy the generated reflect-config.json from temp_resources dir (other json files usually don’t need to be updated and can be ignored)

Next step is to update the documentation

  • create a new .adoc file under data-provider directory

    • copy an existing file from that directory and replace the H2 header to reflect the correct faker provider property name, update the code snippet name (should be in the form of <yml_filename>_provider_dict) in the [source,yaml] section, and update the "available functions" code section as well

Add tests

  • new tests (usually) don’t need to be added since integration tests are dynamically calling all public data provider functions via reflection

  • a few changes need to be made to existing tests though if the new category name was added:

Example commit

In addition to the above instructions, you can also take a look at 0b34d1 commit, which can be used as an MVP example of all of the above steps.