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This project is both a command-line utility and server, used by Codewars to execute small sets of code within various languages, using various testing frameworks.

You can run node run --help to view information about which arguments are supported.


The purpose of this project is to provide a low level ability to run 'Kata'. It provides a mechanism for executing different configurations of code using various languages and testing frameworks.

Docker can be utilized in order to sandbox code execution. A server is provided that can accept 'run' requests and execute them within a Docker container.

Supported Languages and Testing Frameworks

  • JavaScript

    • mocha (coming soon...)
    • codewars
  • CoffeeScript

    • mocha (coming soon...)
    • codewars
  • Ruby

    • rspec
    • codewars
  • Python

    • unittest
    • codewars
  • Java

    • junit
  • C#

    • nunit (coming soon...)
    • codewars
  • Haskell

  • Clojure

  • Julia

  • Erlang

    • (coming soon...)


Basic Usage

The CLI capabilities can be used without having to run Docker. As long as you have the language and frameworks installed on your host machine, you will be able to run the CLI tool standalone.

If you just wanted to execute some code and return its output, you can do so like the following:


node run -l ruby -c 'puts 123'


node run -l js -c 'console.log(123)'


node run -l py -c 'print 123'


node run -l hs -c 'main = putStrLn "123"'


node run -l clj -c '(println 123)'`


node run -l jl -c 'println(123)'


node run -l erl -c 'io:fwrite("123\n"), init:stop().'

Kata Usage

You can also provide a test fixture to be run along with the code. The output returned is the same output that is parsed by Codewars to render its kata output.


node run -l ruby -c 'a = 1' -f 'Test.expect a == 1'


node run -l js -c 'a = 1' -f 'Test.expect(a == 1)'


node run -l py -c 'a = 1' -f 'test.expect(a == 1)'



docker build -t codewars/cli-runner .

Unit testing

docker run -i --entrypoint mocha codewars/cli-runner test/*

Run Help

docker run --rm codewars/cli-runner --help

Run Ruby Kata

docker run --rm codewars/cli-runner run -l ruby -c 'a = 1' -f 'Test.expect a == 1'

Run JavaScript Kata

docker run --rm codewars/cli-runner run -l js -c 'a = 1' -f 'Test.expect(a == 1)'

Run Python Kata

docker run --rm codewars/cli-runner run -l py -c 'a = 1' -f 'test.expect(a == 1)'


You can run a server which wraps the CLI and runs it within a Docker container. If you have Docker installed on your machine and the Codewars image built, all you need to do to start the server is run node server. You can then make posts requests to localhost:8080/run and provide the same arguments that you would for the CLI tool.


Version 1.6.3 or higher is required.

A fully working environment is provided via Vagrant. These steps will get a working server running:

vagrant up
 vagrant ssh
 cd /vagrant
 node build
 supervisor server.js

You should now have a fully working server with Docker support. You can access the server using localhost:8080. You can post requests to /run with the same arguments that the CLI accepts.

Notes about image versioning

The Docker images used by server.js are tagged within a version number. Some utilities have been provided to make it easier to manage versioned images.


Simply run node build to build the latest versioned image

Droplet setup

  • Grab the files

    cd /
    git clone
    cd /codewars-runner/setup
  • Create a non-root user and give it permissions

  • Provision the machine

  • Set up the production environment

  • Set up the hourly docker restart

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