This is my Rubocop setup

.rubocop.yml

# Based on https://gist.github.com/jhass/a5ae80d87f18e53e7b56

AllCops:
  TargetRubyVersion: 2.4
  DisplayCopNames: true
  Include:
    - '**/Rakefile'
    - '**/config.ru'
  Exclude:
    - '**/Guardfile'
    - 'db/**/*'
    - 'config/**/*'
    - 'script/**/*'
    - 'lib/**/*'
    - 'vendor/**/*'
    - 'bin/**/*'
    - 'spec/rails_helper.rb'
    - 'spec/spec_helper.rb'
    - 'node_modules/**/*'


Rails:
  Enabled: true

# Commonly used screens these days easily fit more than 80 characters.
Metrics/LineLength:
  Max: 120
  Exclude:
    -  'spec/**/*'

# Too short methods lead to extraction of single-use methods, which can make
# the code easier to read (by naming things), but can also clutter the class
Metrics/MethodLength:
  Max: 25

# The guiding principle of classes is SRP, SRP can't be accurately measured by LoC
Metrics/ClassLength:
  Max: 1500

# We do not need to support Ruby 1.9, so this is good to use.
Style/SymbolArray:
  Enabled: true

# Mixing the styles looks just silly.
Style/HashSyntax:
  EnforcedStyle: ruby19_no_mixed_keys

# String#% is by far the least verbose and only object oriented variant.
Style/FormatString:
  EnforcedStyle: percent

Style/CollectionMethods:
  Enabled: true
  PreferredMethods:
    # Reduce makes more sense to me.
    reduce: "reduce"

# A specialized exception class will take one or more arguments and construct the message from it.
# So both variants make sense.
Style/RaiseArgs:
  Enabled: false

# Fail is an alias of raise. Avoid aliases, it's more cognitive load for no gain.
# The argument that fail should be used to abort the program is wrong too,
# there's Kernel#abort for that.
Style/SignalException:
  EnforcedStyle: only_raise

# No space makes the method definition shorter and differentiates
# from a regular assignment.
Layout/SpaceAroundEqualsInParameterDefault:
  EnforcedStyle: no_space

# Most readable form.
Layout/AlignHash:
  EnforcedHashRocketStyle: table
  EnforcedColonStyle: table

# Indenting the chained dots beneath each other is not supported by this cop,
# see https://github.com/bbatsov/rubocop/issues/1633
Layout/MultilineOperationIndentation:
  Enabled: false

# Suppressing exceptions can be perfectly fine, and be it to avoid to
# explicitly type nil into the rescue since that's what you want to return,
# or suppressing LoadError for optional dependencies
Lint/HandleExceptions:
  Enabled: false

# { ... } for multi-line blocks is okay, follow Weirichs rule instead:
# https://web.archive.org/web/20140221124509/http://onestepback.org/index.cgi/Tech/Ruby/BraceVsDoEnd.rdoc
Style/BlockDelimiters:
  Enabled: false

# This is more annoying than helpful, honestly
Style/FrozenStringLiteralComment:
  Enabled: false

Style/FileName:
  Exclude:
    - '**/Gemfile'

# do / end blocks should be used for side effects,
# methods that run a block for side effects and have
# a useful return value are rare, assign the return
# value to a local variable for those cases.
Style/MethodCalledOnDoEndBlock:
  Enabled: true

# Enforcing the names of variables? To single letter ones? Just no.
Style/SingleLineBlockParams:
  Enabled: false

# Check with yard instead.
Style/Documentation:
  Enabled: false

# This is just silly. Calling the argument `other` in all cases makes no sense.
Style/OpMethod:
  Enabled: false

# There are valid cases, for example debugging Cucumber steps,
# also they'll fail CI anyway
Lint/Debugger:
  Enabled: false

##  Devise generated controllers

# I am not rewriting the controllers
Style/ClassAndModuleChildren:
  Enabled: false

Metrics/AbcSize:
  Enabled: false

# Specs tend to be very long
Metrics/BlockLength:
  Exclude:
    - "**/*_spec.rb"
    - "spec/**/*"

Metrics/CyclomaticComplexity:
  Exclude:
    - 'app/models/**/*'

Rails/DynamicFindBy:
  Exclude:
    - "features/**/*"