Fukuzatsu (Japanese for "complexity") is a tool for measuring code complexity in Ruby class files. Its analysis generates scores based on cyclomatic complexity algorithms, which in simplest terms measure the number of execution paths through a given piece of code. (You can learn more about cyclomatic complexity here.)

Why should you care about this kind of complexity? More complex code tends to attract bugs and to increase the friction around extending features or refactoring code.

Fukuzatsu was created by Coraline Ada Ehmke and is maintained by Coraline Ada Ehmke, Mike Ziwisky, and the team at Instructure. It was originally inspired by Saikuro, written by Zev Blut.


These are screenshots of the -f html output. First, the overall project summary:

Project Summary

Then the detail view of a single class:

Project Summary


Install the gem:

$ gem install fukuzatsu

This installs the CLI tool.


fuku check path/to/file/my_file.rb

fuku check path/to/directory
# Generates report for all rb files in the given directory

fuku check path/to/file/my_file.rb -f html
# Writes to doc/fuzuzatsu/htm/index.htm

fuku check path/to/file/my_file.rb -f csv
# Writes to doc/fuzuzatsu/csv/results.csv

fuku check path/to/file/my_file.rb -f json
# Writes to doc/fuzuzatsu/json/results.json

Running as docker image

The following will download the latest docker image, mount the current directory inside the container and run fuku check -f html . which generates html report for all ruby files in the current directory.

docker run -v $(pwd):/tmp/fuku --workdir=/tmp/fuku rubygem/fukuzatsu check -f html .


Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request