In RuboCop lingo the various checks performed on the code are called cops. There are several cop departments.

You can also load custom cops.


Most of the cops in RuboCop are so called style cops that check for stylistic problems in your code. Almost all of the them are based on the Ruby Style Guide. Many of the style cops have configurations options allowing them to support different popular coding conventions.


Lint cops check for possible errors and very bad practices in your code. RuboCop implements in a portable way all built-in MRI lint checks (ruby -wc) and adds a lot of extra lint checks of its own. You can run only the lint cops like this:

$ rubocop -l

The -l/--lint option can be used together with --only to run all the enabled lint cops plus a selection of other cops.

Disabling any of the lint cops is generally a bad idea.


Metrics cops deal with properties of the source code that can be measured, such as class length, method length, etc. Generally speaking, they have a configuration parameter called Max and when running rubocop --auto-gen-config, this parameter will be set to the highest value found for the inspected code.


Performance cops catch Ruby idioms which are known to be slower than another equivalent (and equally readable) idiom.


Rails cops are specific to the Ruby on Rails framework. Unlike all other cop types they are not used by default and you have to request them specifically:

$ rubocop -R

or add the following directive to your .rubocop.yml:

  Enabled: true


Bundler cops check for style or bad practices in Bundler files, e.g. Gemfile.

Available cops

In the following section you find all available cops:

Department Bundler

Department Layout

Department Lint

Department Metrics

Department Performance

Department Rails

Department Security

Department Style