Basic Usage

RuboCop has three primary uses:

  1. Code style checker (a.k.a. linter)

  2. A replacement for ruby -w (a subset of its linting capabilities)

  3. Code formatter

In the next sections we’ll briefly cover all of them.

Code style checker

Running rubocop with no arguments will check all Ruby source files in the current directory:

$ rubocop

Alternatively you can pass rubocop a list of files and directories to check:

$ rubocop app spec lib/something.rb

Here’s RuboCop in action. Consider the following Ruby source code:

def badName
  if something

Running RuboCop on it (assuming it’s in a file named test.rb) would produce the following report:

Inspecting 1 file


test.rb:1:1: C: Style/FrozenStringLiteralComment: Missing magic comment # frozen_string_literal: true.
def badName
test.rb:1:5: C: Naming/MethodName: Use snake_case for method names.
def badName
test.rb:2:3: C: Style/GuardClause: Use a guard clause instead of wrapping the code inside a conditional expression.
  if something
test.rb:2:3: C: Style/IfUnlessModifier: Favor modifier if usage when having a single-line body. Another good alternative is the usage of control flow &&/||.
  if something
test.rb:4:5: W: Layout/EndAlignment: end at 4, 4 is not aligned with if at 2, 2.

1 file inspected, 5 offenses detected

Autocorrecting offenses

You can also run RuboCop in an autocorrect mode, where it will try to automatically fix the problems it found in your code:

$ rubocop -a
# or
$ rubocop --autocorrect
See Autocorrect for more details.

Changing what RuboCop considers to be offenses

RuboCop comes with a preconfigured set of rules for each of its cops, based on the Ruby Style Guide. Depending on your project, you may wish to reconfigure a cop, tell to ignore certain files, or disable it altogether.

The most common way to change RuboCop’s behavior is to create a configuration file named .rubocop.yml in the project’s root directory.

For more information, see Configuration.

RuboCop as a replacement for ruby -w

RuboCop natively implements almost all ruby -w lint warning checks, and then some. If you want you can use RuboCop simply as a replacement for ruby -w:

$ rubocop -l
# or
$ rubocop --lint

RuboCop as a formatter

There’s a handy shortcut to run autocorrection only on code layout (a.k.a. formatting) offenses:

$ rubocop -x
# or
$ rubocop --fix-layout
This option was introduced in RuboCop 0.57.0.

Command-line flags

For more details check the available command-line options:

$ rubocop -h

To specify multiple cops for one flag, separate cops with commas and no spaces:

$ rubocop --only Rails/Blank,Layout/HeredocIndentation,Naming/FileName
Command flag Description


Autocorrect offenses (only when it’s safe). See Autocorrect.


Deprecated alias of -a/--autocorrect.


Autocorrect offenses (safe and unsafe). See Autocorrect.


Deprecated alias of -A/--autocorrect-all.


Generate a configuration file acting as a TODO list.


Force color output on or off.


Run with specified config file.


Store and reuse results for faster operation.


Displays some extra debug output.


Run without pending cops.


Used with --autocorrect to annotate any offenses that do not support autocorrect with rubocop:todo comments.


Displays cop names in offense messages. Default is true.


Only output offense messages at the specified --fail-level or above.


Only output correctable offense messages.


Only output safe correctable offense messages.


Run with pending cops.


Run all cops enabled by configuration except the specified cop(s) and/or departments.


Limit how many individual files --auto-gen-config can list in Exclude parameters, default is 15.


Displays extra details in offense messages.


Choose a formatter, see Formatters.


Inspect files in order of modification time and stops after first file with offenses.


Minimum severity for exit with error code. Full severity name or upper case initial can be given. Normally, autocorrected offenses are ignored. Use A or autocorrect if you’d like them to trigger failure.


Force excluding files specified in the configuration Exclude even if they are explicitly passed as arguments.


Inspect files given on the command line only if they are listed in AllCops/Include parameters of user configuration or default configuration.


Print usage information.


Ignores all Exclude: settings from all .rubocop.yml files present in parent folders. This is useful when you are importing submodules when you want to test them without being affected by the parent module’s rubocop settings.


Ignore unrecognized cops or departments in the config.


Generate a .rubocop.yml file in the current directory.


Run only lint cops.


List all files RuboCop will inspect.


Generate only Exclude parameters and not Max when running --auto-gen-config, except if the number of files with offenses is bigger than exclude-limit. Default is false


Include the date and time when --auto-gen-config was run in the config file it generates. Default is true.


Show offense counts in config file generated by --auto-gen-config. Default is true.


Run only the specified cop(s) and/or cops in the specified departments.


Write output to a file instead of STDOUT.


Use available CPUs to execute inspection in parallel. Default is parallel.


Raise cop-related errors with cause and location. This is used to prevent cops from failing silently. Default is false.


Require Ruby file (see Loading Extensions).


Regenerate the TODO list using the same options as the last time it was generated with --auto-gen-config (generation options can be overridden).


Run only safe cops.


Deprecated alias of -a/--autocorrect.


Shows available cops and their configuration.


Shows urls for documentation pages of supplied cops.


Write all output to stderr except for the autocorrected source. This is especially useful when combined with --autocorrect and --stdin.


Pipe source from STDIN. This is useful for editor integration. Takes one argument, a path, relative to the root of the project. RuboCop will use this path to determine which cops are enabled (via eg. Include/Exclude), and so that certain cops like Naming/FileName can be checked.


Display style guide URLs in offense messages.


Autocorrect only code layout (formatting) offenses.


Displays the current version and exits.


Displays the current version plus the version of Parser and Ruby.

Default command-line options are loaded from .rubocop and RUBOCOP_OPTS and are combined with command-line options that are explicitly passed to rubocop. Thus, the options have the following order of precedence (from highest to lowest):

  1. Explicit command-line options

  2. Options from RUBOCOP_OPTS environment variable

  3. Options from .rubocop file.

Exit codes

RuboCop exits with the following status codes:

  • 0 if no offenses are found or if the severity of all offenses are less than --fail-level. (By default, if you use --autocorrect, offenses which are autocorrected do not cause RuboCop to fail.)

  • 1 if one or more offenses equal or greater to --fail-level are found. (By default, this is any offense which is not autocorrected.)

  • 2 if RuboCop terminates abnormally due to invalid configuration, invalid CLI options, or an internal error.