Static code analysis for Ruby (not actively maintained).
Latest commit 87842ae Mar 3, 2017 @jwilk jwilk committed with Fix typos


ruby-lint is a static code analysis tool for Ruby. It is inspired by tools such as jshint, flake8 and similar tools. ruby-lint primarily focuses on logic related errors such as the use of non existing variables instead of focusing on semantics (e.g. the amount of characters per line).

The features of ruby-lint include but are not limited to the detection of unused variables, the use of undefined methods and method calls with invalid argument amounts and more. More in-depth analysis will be added over time.

The aim of ruby-lint is to provide analysis that is as accurate as possible. However, due to the dynamic nature of Ruby and the sheer amount of meta-magic in third-party code there will at times be false positives. Analysis can be improved by documenting your code using YARD, in particular the @param and @return tags are used by ruby-lint to obtain extra information when processing methods.


  • a Ruby implementation running 1.9 or newer
  • a Unix based Operating System

The following Ruby implementations/versions are officially supported:

  • MRI 1.9.3, 2.0 or 2.1
  • Rubinius 2.0 and newer
  • Jruby 1.7 and newer

Ruby implementations running a 1.8 based version of Ruby are not supported.


The easiest way to install ruby-lint is to install it from RubyGems:

gem install ruby-lint

If you prefer to install (and build) ruby-lint from the source code you can do so as following:

git clone git://
cd ruby-lint
bundle install # you can also install the dependencies manually
rake build

This builds a new version of the Gem and saves it in the pkg/ directory.


Using ruby-lint from the CLI is very easy. To analyze a set of files you run the following:

ruby-lint file1.rb file2.rb

For more information specify either the -h or --help option.


Given the following code:

class Person
  def initialize(name)
    # oops, not setting @name

  def greet
    return "Hello, #{@name}"

user     ='Alice')
greeting = user.greet


Analysing this file using ruby-lint (with the default settings) would result in the following output:

test.rb: error: line 7, column 22: undefined instance variable @name
test.rb: warning: line 12, column 1: unused local variable greeting
test.rb: error: line 14, column 1: wrong number of arguments for 'greet' (expected 0 but got 1)

ruby-lint versus RuboCop

A question commonly asked is what purpose ruby-lint serves compared to other tools such as RuboCop. After all, upon first sight the two tools look pretty similar.

The big difference between ruby-lint and RuboCop is that ruby-lint focuses primarily on technical problems such as the use of undefined methods/variables, unused variables/method arguments and more. RuboCop on the other hand focuses mostly on style related issues based on a community driven Ruby style guide. This means that it will for example warn you about methods written using camelCase and method bodies that are considered to be too long.

Personally I have little interest in adding style related analysis as RuboCop already does that and in my opinion does a far better job at it. I also simply think it's too boring to write analysis like this. Having said that, ruby-lint has some basic style related analysis (e.g. the use of BEGIN) but this mostly serves as a simple example on how to write analysis code.

In the end it depends on what your needs are. If you have a team that's having trouble following a consistent coding style then RuboCop is probably the right tool for the job. On the other hand, if you're trying to debug a nasty bug then ruby-lint will most likely be more useful.


As a basic form of security ruby-lint provides a set of SHA512 checksums for every Gem release. These checksums can be found in the checksum/ directory. Although these checksums do not prevent malicious users from tampering with a built Gem they can be used for basic integrity verification purposes.

The checksum of a file can be checked using the sha512sum command. For example:

$ sha512sum pkg/ruby-lint-0.9.1.gem
10a51f27c455e5743fff7fefe29512cff20116b805bec148e09d4bade1727e3beab7f7f9ee97b020d290773edcb7bd1685858ccad0bbd1a35cc0282c00c760c6  pkg/ruby-lint-0.9.1.gem

In the past Gems were also signed using PGP, this is no longer the case.


  • {file:CONTRIBUTING Contributing}
  • {file:architecture Architecture}
  • {file:code_analysis Code Analysis}
  • {file:configuration Configuration}
  • {file:definitions Definitions}


All source code in this repository is subject to the terms of the Mozilla Public License, version 2.0 unless stated otherwise. A copy of this license can be found the file "LICENSE" or at