Configuration

The behavior of RuboCop can be controlled via the .rubocop.yml configuration file. It makes it possible to enable/disable certain cops (checks) and to alter their behavior if they accept any parameters. The file can be placed in your home directory, XDG config directory, or in some project directory.

The file has the following format:

inherit_from: ../.rubocop.yml

Style/Encoding:
  Enabled: false

Layout/LineLength:
  Max: 99
Qualifying cop name with its type, e.g., Style, is recommended, but not necessary as long as the cop name is unique across all types.

Config file locations

RuboCop will start looking for the configuration file in the directory where the inspected file is and continue its way up to the root directory.

If it cannot be found until reaching the project’s root directory, then it will be searched for in the .config directory of the project root and the user’s global config locations. The user’s global config locations consist of a dotfile or a config file inside the XDG Base Directory specification.

  • .config/.rubocop.yml or .config/rubocop/config.yml at the project root

  • ~/.rubocop.yml

  • $XDG_CONFIG_HOME/rubocop/config.yml (expands to ~/.config/rubocop/config.yml if $XDG_CONFIG_HOME is not set)

If both files exist, the dotfile will be selected.

As an example, if RuboCop is invoked from inside /path/to/project/lib/utils, then RuboCop will use the config as specified inside the first of the following files:

  • /path/to/project/lib/utils/.rubocop.yml

  • /path/to/project/lib/.rubocop.yml

  • /path/to/project/.rubocop.yml

  • /path/to/project/.config/.rubocop.yml

  • /path/to/project/.config/rubocop/config.yml

  • /.rubocop.yml

  • ~/.rubocop.yml

  • ~/.config/rubocop/config.yml

  • RuboCop’s default configuration

All the previous logic does not apply if a specific configuration file is passed on the command line through the --config flag. In that case, the resolved configuration file will be the one passed to the CLI.

Inheritance

All configuration inherits from RuboCop’s default configuration (See "Defaults").

RuboCop also supports inheritance in user’s configuration files. The most common example would be the .rubocop_todo.yml file (See "Automatically Generated Configuration" below).

Settings in the child file (that which inherits) override those in the parent (that which is inherited), with the following caveats.

Inheritance of hashes vs. other types

Configuration parameters that are hashes, for example PreferredMethods in Style/CollectionMethods, are merged with the same parameter in the parent configuration. This means that any key-value pairs given in child configuration override the same keys in parent configuration. Giving ~, YAML’s representation of nil, as a value cancels the setting of the corresponding key in the parent configuration. For example:

Style/CollectionMethods:
  Enabled: true
  PreferredMethods:
    # No preference for collect, keep all others from default config.
    collect: ~

Other types, such as AllCops / Include (an array), are overridden by the child setting.

Arrays override because if they were merged, there would be no way to remove elements in child files.

However, advanced users can still merge arrays using the inherit_mode setting. See "Merging arrays using inherit_mode" below.

Inheriting from another configuration file in the project

The optional inherit_from directive is used to include configuration from one or more files. This makes it possible to have the common project settings in the .rubocop.yml file at the project root, and then only the deviations from those rules in the subdirectories. The files can be given with absolute paths or paths relative to the file where they are referenced. The settings after an inherit_from directive override any settings in the file(s) inherited from. When multiple files are included, the first file in the list has the lowest precedence and the last one has the highest. The format for multiple inheritance is:

inherit_from:
  - ../.rubocop.yml
  - ../conf/.rubocop.yml

inherit_from also accepts a glob, for example:

inherit_from:
  - packages/*/.rubocop_todo.yml

The example above is one potential use-case: allowing components within your repo to organize their own .rubocop_todo.yml files.

Inheriting configuration from a remote URL

The optional inherit_from directive can contain a full url to a remote file. This makes it possible to have common project settings stored on a http server and shared between many projects.

The remote config file is cached locally and is only updated if:

  • The file does not exist.

  • The file has not been updated in the last 24 hours.

  • The remote copy has a newer modification time than the local copy.

You can inherit from both remote and local files in the same config and the same inheritance rules apply to remote URLs and inheriting from local files where the first file in the list has the lowest precedence and the last one has the highest. The format for multiple inheritance using URLs is:

inherit_from:
  - http://www.example.com/rubocop.yml
  - ../.rubocop.yml

You can inherit from a repo with basic auth that is authorized to access the repo as follow:

inherit_from:
  - http://<user_name>:<password>@raw.github.com/example/rubocop.yml

A GitHub personal access token can also be configured as follow:

inherit_from:
  - http://<personal_access_token>@raw.github.com/example/rubocop.yml

Inheriting configuration from a dependency gem

The optional inherit_gem directive is used to include configuration from one or more gems external to the current project. This makes it possible to inherit a shared dependency’s RuboCop configuration that can be used from multiple disparate projects.

Configurations inherited in this way will be essentially prepended to the inherit_from directive, such that the inherit_gem configurations will be loaded first, then the inherit_from relative file paths will be loaded (overriding the configurations from the gems), and finally the remaining directives in the configuration file will supersede any of the inherited configurations. This means the configurations inherited from one or more gems have the lowest precedence of inheritance.

The directive should be formatted as a YAML Hash using the gem name as the key and the relative path within the gem as the value:

inherit_gem:
  my-shared-gem: .rubocop.yml
  cucumber: conf/rubocop.yml

An array can also be used as the value to include multiple configuration files from a single gem:

inherit_gem:
  my-shared-gem:
    - default.yml
    - strict.yml
If the shared dependency is declared using a Bundler Gemfile and the gem was installed using bundle install, it would be necessary to also invoke RuboCop using Bundler in order to find the dependency’s installation path at runtime: 
$ bundle exec rubocop <options...>

Merging arrays using inherit_mode

The optional directive inherit_mode specifies which configuration keys that have array values should be merged together instead of overriding the inherited value.

This applies to explicit inheritance using inherit_from as well as implicit inheritance from the default configuration.

Given the following config:

# .rubocop.yml
inherit_from:
  - shared.yml

inherit_mode:
  merge:
    - Exclude

AllCops:
  Exclude:
    - 'generated/**/*.rb'

Style/For:
  Exclude:
    - bar.rb
# .shared.yml
Style/For:
  Exclude:
    - foo.rb

The list of Excludes for the Style/For cop in this example will be ['foo.rb', 'bar.rb']. Similarly, the AllCops:Exclude list will contain all the default patterns plus the generated/**/*.rb entry that was added locally.

The directive can also be used on individual cop configurations to override the global setting.

inherit_from:
  - shared.yml

inherit_mode:
  merge:
    - Exclude

Style/For:
  inherit_mode:
    override:
      - Exclude
  Exclude:
    - bar.rb

In this example the Exclude would only include bar.rb.

Pre-processing

Configuration files are pre-processed using the ERB templating mechanism. This makes it possible to add dynamic content that will be evaluated when the configuration file is read. For example, you could let RuboCop ignore all files ignored by Git.

AllCops:
  Exclude:
  <% `git status --ignored --porcelain`.lines.grep(/^!! /).each do |path| %>
    - <%= path.sub(/^!! /, '').sub(/\/$/, '/**/*') %>
  <% end %>

Defaults

The file config/default.yml under the RuboCop home directory contains the default settings that all configurations inherit from. Project and personal .rubocop.yml files need only make settings that are different from the default ones. If there is no .rubocop.yml file in the project, home or XDG directories, config/default.yml will be used.

Including/Excluding files

RuboCop does a recursive file search starting from the directory it is run in, or directories given as command line arguments. Files that match any pattern listed under AllCops/Include and extensionless files with a hash-bang (#!) declaration containing one of the known ruby interpreters listed under AllCops/RubyInterpreters are inspected, unless the file also matches a pattern in AllCops/Exclude. Hidden directories (i.e., directories whose names start with a dot) are not searched by default.

Here is an example that might be used for a Rails project:

AllCops:
  Exclude:
    - 'db/**/*'
    - 'config/**/*'
    - 'script/**/*'
    - 'bin/{rails,rake}'
    - !ruby/regexp /old_and_unused\.rb$/

# other configuration
# ...
When inspecting a certain directory(or file) given as RuboCop’s command line arguments, patterns listed under AllCops / Exclude are also inspected. If you want to apply AllCops / Exclude rules in this circumstance, add --force-exclusion to the command line argument.

Here is an example:

# .rubocop.yml
AllCops:
  Exclude:
    - foo.rb

If foo.rb specified as a RuboCop’s command line argument, the result is:

# RuboCop inspects foo.rb.
$ bundle exec rubocop foo.rb

# RuboCop does not inspect foo.rb.
$ bundle exec rubocop --force-exclusion foo.rb

Path relativity

In .rubocop.yml and any other configuration file beginning with .rubocop, files, and directories are specified relative to the directory where the configuration file is. In configuration files that don’t begin with .rubocop, e.g. our_company_defaults.yml, paths are relative to the directory where rubocop is run.

This affects cops that have customisable paths: if the default is db/migrate/*.rb, and the cop is enabled in db/migrate/.rubocop.yml, the path will need to be explicitly set as *.rb, as the default will look for db/migrate/db/migrate/*.rb. This is unlikely to be what you wanted.

Unusual files, that would not be included by default

RuboCop comes with a comprehensive list of common ruby file names and extensions. But, if you’d like RuboCop to check files that are not included by default, you’ll need to pass them in on the command line, or to add entries for them under AllCops/Include. Remember that your configuration files override RuboCops’s defaults. In the following example, we want to include foo.unusual_extension, but we also must copy any other patterns we need from the overridden default.yml.

AllCops:
  Include:
    - foo.unusual_extension
    - '**/*.rb'
    - '**/*.gemfile'
    - '**/*.gemspec'
    - '**/*.rake'
    - '**/*.ru'
    - '**/Gemfile'
    - '**/Rakefile'

This behavior of Include (overriding default.yml) was introduced in 0.56.0 via #5882. This change allows people to include/exclude precisely what they need to, without the defaults getting in the way.

Another example, using inherit_mode

inherit_mode:
  merge:
    - Include

AllCops:
  Include:
    - foo.unusual_extension

See "Merging arrays using inherit_mode" above.

Deprecated patterns

Patterns that are just a file name, e.g. Rakefile, will match that file name in any directory, but this pattern style is deprecated. The correct way to match the file in any directory, including the current, is **/Rakefile.

The pattern config/** will match any file recursively under config, but this pattern style is deprecated and should be replaced by config/**/*.

Include and Exclude are relative to their directory

The Include and Exclude parameters are special. They are valid for the directory tree starting where they are defined. They are not shadowed by the setting of Include and Exclude in other .rubocop.yml files in subdirectories. This is different from all other parameters, who follow RuboCop’s general principle that configuration for an inspected file is taken from the nearest .rubocop.yml, searching upwards.

This behavior will be overridden if you specify the --ignore-parent-exclusion command line argument.

Cop-specific Include and Exclude

Cops can be run only on specific sets of files when that’s needed (for instance you might want to run some Rails model checks only on files whose paths match app/models/*.rb). All cops support the Include param.

Rails/HasAndBelongsToMany:
  Include:
    - app/models/*.rb

Cops can also exclude only specific sets of files when that’s needed (for instance you might want to run some cop only on a specific file). All cops support the Exclude param.

Rails/HasAndBelongsToMany:
  Exclude:
    - app/models/problematic.rb

Generic configuration parameters

In addition to Include and Exclude, the following parameters are available for every cop.

Enabled

Specific cops can be disabled by setting Enabled to false for that specific cop.

Layout/LineLength:
  Enabled: false

Most cops are enabled by default. Cops, introduced or significantly updated between major versions, are in a special pending status (read more in "Versioning"). Some cops, configured the above Enabled: false in config/default.yml, are disabled by default.

The cop enabling process can be altered by setting DisabledByDefault or EnabledByDefault (but not both) to true. These settings override the default for all cops to disabled or enabled, except Lint/Syntax which is always enabled, regardless of the cops' default values (whether enabled, disabled or pending).

AllCops:
  DisabledByDefault: true

All cops except Lint/Syntax are then disabled by default. Only cops appearing in user configuration files with Enabled: true will be enabled; every other cop will be disabled without having to explicitly disable them in configuration. It is also possible to enable entire departments by adding for example

Style:
  Enabled: true

All cops in the Style department are then enabled.

If a department is disabled, cops in that department can still be individually enabled, and that setting overrides the setting for its department in the same configuration file and in any inherited file.

inherit_from: config_that_disables_the_metrics_department.yml

Metrics/MethodLength:
  Enabled: true

Style:
  Enabled: false

Style/Alias:
  Enabled: true

Severity

Each cop has a default severity level based on which department it belongs to. The level is normally warning for Lint and convention for all the others, but this can be changed in user configuration. Cops can customize their severity level. Allowed values are info, refactor, convention, warning, error and fatal.

Cops with severity info will be reported but will not cause rubocop to return a non-zero value.

There is one exception from the general rule above and that is Lint/Syntax, a special cop that checks for syntax errors before the other cops are invoked. It cannot be disabled and its severity (fatal) cannot be changed in configuration.

Lint:
  Severity: error

Metrics/CyclomaticComplexity:
  Severity: warning

Details

Individual cops can be embellished with extra details in offense messages:

Layout/LineLength:
  Details: >-
    If lines are too short, text becomes hard to read because you must
    constantly jump from one line to the next while reading. If lines are too
    long, the line jumping becomes too hard because you "lose the line" while
    going back to the start of the next line. 80 characters is a good
    compromise.

These details will only be seen when RuboCop is run with the --extra-details flag or if ExtraDetails is set to true in your global RuboCop configuration.

AutoCorrect

Cops that support the --autocorrect option offer flexible settings for autocorrection. These settings can be specified in the configuration file as follows:

  • always

  • contextual

  • disabled

always (Default)

This setting enables autocorrection always by default. For backward compatibility, true is treated the same as always.

Style/PerlBackrefs:
  AutoCorrect: always # or true

contextual

This setting enables autocorrection when launched from the rubocop command, but it is not available through LSP. e.g., rubocop --lsp, rubocop --editor-mode, or a program where RuboCop::LSP.enable has been applied.

Inspections via the command line are treated as code that has been finalized.

Style/PerlBackrefs:
  AutoCorrect: contextual

This setting prevents autocorrection during editing in the editor.

disabled

This setting disables autocorrection. For backward compatibility, false is treated the same as disabled.

Style/PerlBackrefs:
  AutoCorrect: disabled # or false

Common configuration parameters

There are some configuration parameters that are shared by many cops, with the same behavior.

IgnoredMethods

Cops that evaluate methods can often be configured to ignore certain methods. Both strings and regular expressions can be used. For example:

Metrics/BlockLength:
  IgnoredMethods:
    - refine
    - !ruby/regexp /\b(class|instance)_methods\b/

Setting the target Ruby version

Some checks are dependent on the version of the Ruby interpreter which the inspected code must run on. For example, enforcing using Ruby 2.6+ endless ranges foo[n..] rather than foo[n..-1] can help make your code shorter and more consistent…​ unless it must run on e.g. Ruby 2.5.

Users may let RuboCop know the oldest version of Ruby which your project supports with:

AllCops:
  TargetRubyVersion: 2.5
When ParserEngine: parser_prism is specified, the values that can be assigned to TargetRubyVersion must be 3.3 or higher.

Otherwise, RuboCop will then check your project for a series of files where the version may be specified already. The files that will be looked for are *.gemspec, .ruby-version, .tool-versions, and Gemfile.lock. If Gemspec file has an array for required_ruby_version, the lowest version will be used. If none of the files are found a default version value will be used.

Setting the parser engine

The parser engine configuration was introduced in RuboCop 1.62. This experimental feature has been under consideration for a while.

RuboCop allows switching the backend parser by specifying either parser_whitequark or parser_prism for the ParserEngine.

Here are the parsers used as backends for each value:

By default, parser_whitequark is implicitly used.

parser_whitequark can analyze source code from Ruby 2.0 and above:

AllCops:
  ParserEngine: parser_whitequark

parser_prism can analyze source code from Ruby 3.3 and above:

AllCops:
  ParserEngine: parser_prism
  TargetRubyVersion: 3.3

parser_prism tends to perform analysis faster than parser_whitequark.

Since the use of Prism is experimental, it is not included in RuboCop’s runtime dependencies. If running through Bundler, please first add gem 'prism' to your Gemfile: 
gem 'prism'

There are some incompatibilities with parser_whitequark, making it still considered experimental. For known issues, please refer to the Prism issues: https://github.com/ruby/prism/issues?q=is%3Aissue+is%3Aopen+label%3Arubocop

Automatically Generated Configuration

If you have a code base with an overwhelming amount of offenses, it can be a good idea to use rubocop --auto-gen-config, which creates .rubocop_todo.yml and adds inherit_from: .rubocop_todo.yml in your .rubocop.yml. The generated file .rubocop_todo.yml contains configuration to disable cops that currently detect an offense in the code by changing the configuration for the cop, excluding the offending files, or disabling the cop altogether once a file count limit has been reached.

By adding the option --exclude-limit COUNT, e.g., rubocop --auto-gen-config --exclude-limit 5, you can change how many files are excluded before the cop is entirely disabled. The default COUNT is 15. If you don’t want the cop to be entirely disabled regardless of the number of files, use the --no-exclude-limit option, e.g., rubocop --auto-gen-config --no-exclude-limit.

The next step is to cut and paste configuration from .rubocop_todo.yml into .rubocop.yml for everything that you think is in line with your (organization’s) code style and not a good fit for a todo list. Pay attention to the comments above each entry. They can reveal configuration parameters such as EnforcedStyle, which can be used to modify the behavior of a cop instead of disabling it completely.

Then you can start removing the entries in the generated .rubocop_todo.yml file one by one as you work through all the offenses in the code. You can also regenerate your .rubocop_todo.yml using the same options by running rubocop --regenerate-todo.

Another way of silencing offense reports, aside from configuration, is through source code comments. These can be added manually or automatically. See "Disabling Cops within Source Code" below.

The cops in the Metrics department will by default get Max parameters generated in .rubocop_todo.yml. The value of these will be just high enough so that no offenses are reported the next time you run rubocop. If you prefer to exclude files, like for other cops, add --auto-gen-only-exclude when running with --auto-gen-config. It will still change the maximum if the number of excluded files is higher than the exclude limit.

Some cops have a configurable option named EnforcedStyle. By default, when generating the .rubocop_todo.yml, if one style is used for all files, these cops will add the settings for the style being used. If you want to excluded on a file-by-file basis, add the --no-auto-gen-enforced-style option along with --auto-gen-config.

Updating the configuration file

When you update RuboCop version, sometimes you need to change .rubocop.yml. If you use mry, you can update .rubocop.yml to latest version automatically.

$ gem install mry
# Update to latest version
$ mry .rubocop.yml
# Update to specified version
$ mry --target=0.48.0 .rubocop.yml

See https://github.com/pocke/mry for more information.

Disabling Cops within Source Code

One or more individual cops can be disabled locally in a section of a file by adding a comment such as

# rubocop:disable Layout/LineLength, Style/StringLiterals
[...]
# rubocop:enable Layout/LineLength, Style/StringLiterals

You can also disable entire departments by giving a department name in the comment.

# rubocop:disable Metrics, Layout/LineLength
[...]
# rubocop:enable Metrics, Layout/LineLength

You can also disable all cops with

# rubocop:disable all
[...]
# rubocop:enable all

In cases where you want to differentiate intentionally-disabled cops vs. cops you’d like to revisit later, you can use rubocop:todo as an alias of rubocop:disable.

# rubocop:todo Layout/LineLength, Style/StringLiterals
[...]
# rubocop:enable Layout/LineLength, Style/StringLiterals

One or more cops can be disabled on a single line with an end-of-line comment.

for x in (0..19) # rubocop:disable Style/For

If you want to disable a cop that inspects comments, you can do so by adding an "inner comment" on the comment line.

# coding: utf-8 # rubocop:disable Style/Encoding

Running rubocop --autocorrect --disable-uncorrectable will create comments to disable all offenses that can’t be automatically corrected.

Do not write anything other than cop name in the disabling comment. E.g.:

# rubocop:disable Layout/LineLength --This is a bad comment that includes other than cop name.

Temporarily enabling cops in source code

In a similar way to disabling cops within source code, you can also temporarily enable specific cops if you want to enforce specific rules for part of the totality of a file.

Let’s use the cop Style/AsciiComments, which is by default Enabled: false. If you want a specific file to have ASCII-only comments to be compatible with some specific post-processing.

# rubocop:enable Style/AsciiComments
# If applicable, leave a comment to others explaining the rationale:
# We need the comments to remain ASCII only for compatibility with lib/post_processor.rb

class Restaurant
  # This comment has to be ASCII-only because of the rubocop:enable directive
  def menu
    return dishes.map(&:humanize)
  end
end

You can also enforce the same for part of a file by disabling the cop afterwards

class Dish
  def humanize
    return [
      "Delicious #{self.name}"
      *ingredients
    ].join("\n")
  end
end

# rubocop:enable Style/AsciiComments
# If applicable, leave a comment to others explaining the rationale:
# We need the comments to remain ASCII only for compatibility with lib/post_processor.rb

class Restaurant
  # This comment has to be ASCII-only because of the rubocop:enable directive
  def menu
    return dishes.map(&:humanize)
  end
end

# rubocop:disable Style/AsciiComments

class Ingredient
  # Notice how the comment below is non-ASCII
  # Gets rid of odd characters like 😀, ͸
  def sanitize
    self.name.gsub(/[^a-z]/, '')
  end
end

Setting the style guide URL

You can specify the base URL of the style guide using StyleGuideBaseURL. If specified under AllCops, all cops are targeted.

AllCops:
  StyleGuideBaseURL: https://rubystyle.guide

StyleGuideBaseURL is combined with StyleGuide specified to the cop.

Lint/UselessAssignment:
  StyleGuide: '#underscore-unused-vars'

The style guide URL is https://rubystyle.guide#underscore-unused-vars.

If specified under a specific department, it takes precedence over AllCops. The following is an example of specifying Rails department.

Rails:
  StyleGuideBaseURL: https://rails.rubystyle.guide
Rails/TimeZone:
  StyleGuide: '#time'

The style guide URL is https://rails.rubystyle.guide#time.

Setting the documentation URL

You can specify the base URL of the documentation using DocumentationBaseURL. If specified under AllCops, all cops are targeted.

AllCops:
  DocumentationBaseURL: https://docs.rubocop.org/rubocop

If specified under a specific department, it takes precedence over AllCops. The following is an example of specifying Rails department.

Rails:
  DocumentationBaseURL: https://docs.rubocop.org/rubocop-rails

Enable checking Active Support extensions

Some cops for checking specified methods (e.g. Style/HashExcept) supports Active Support extensions. This is off by default, but can be enabled by the ActiveSupportExtensionsEnabled option.

AllCops:
  ActiveSupportExtensionsEnabled: true