diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 17554a4a..41337e5e 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -16,3 +16,16 @@ jobs:
       uses: ludeeus/action-shellcheck@1.1.0
       with:
         scandir: './bin'
+  rubocop:
+    runs-on: ubuntu-latest
+    env:
+      BUNDLE_WITHOUT: development:test
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        bundler-cache: true
+    - name: Run tests
+      run: bundle exec rake rubocop
diff --git a/.gitignore b/.gitignore
index 1f85efba..3055395b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@
 # Ignore bundler config.
 /.bundle
 /vendor
+/.vendor
 
 # Ignore the default SQLite database.
 /db/*.sqlite3
diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 00000000..d3eabd85
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,13 @@
+---
+inherit_from: .rubocop_todo.yml
+
+require: rubocop-rails
+
+AllCops:
+  TargetRubyVersion: 2.5
+  NewCops: enable
+  Include:
+    - '**/*.rb'
+  Exclude:
+    - vendor/**/*
+    - .vendor/**/*
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
new file mode 100644
index 00000000..501d2c79
--- /dev/null
+++ b/.rubocop_todo.yml
@@ -0,0 +1,702 @@
+---
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2022-04-07 09:17:26 UTC using RuboCop version 1.25.0.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
+# Offense count: 12
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: with_first_argument, with_fixed_indentation
+Layout/ArgumentAlignment:
+  Exclude:
+    - 'app/controllers/keys_controller.rb'
+    - 'app/models/hiera_data/data_file.rb'
+    - 'bin/webpack'
+    - 'bin/webpack-dev-server'
+    - 'test/controllers/keys_controller_test.rb'
+    - 'test/integration/required_authentication_test.rb'
+
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: with_first_element, with_fixed_indentation
+Layout/ArrayAlignment:
+  Exclude:
+    - 'app/services/puppet_db_client.rb'
+    - 'config/initializers/friendly_id.rb'
+
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentOneStep, IndentationWidth.
+# SupportedStyles: case, end
+Layout/CaseIndentation:
+  Exclude:
+    - 'app/helpers/application_helper.rb'
+
+# Offense count: 12
+# Cop supports --auto-correct.
+Layout/EmptyLineAfterGuardClause:
+  Exclude:
+    - 'app/models/hiera_data/config.rb'
+    - 'app/models/hiera_data/hierarchy.rb'
+    - 'app/models/hiera_data/interpolation.rb'
+    - 'app/models/hiera_data/yaml_file.rb'
+    - 'bin/bundle'
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EmptyLineBetweenMethodDefs, EmptyLineBetweenClassDefs, EmptyLineBetweenModuleDefs, AllowAdjacentOneLineDefs, NumberOfEmptyLines.
+Layout/EmptyLineBetweenDefs:
+  Exclude:
+    - 'test/models/hiera_data/config_test.rb'
+    - 'test/models/hiera_data/hierarchy_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Layout/EmptyLines:
+  Exclude:
+    - 'test/models/hiera_data/hierarchy_test.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: around, only_before
+Layout/EmptyLinesAroundAccessModifier:
+  Exclude:
+    - 'app/controllers/users_controller.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowAliasSyntax, AllowedMethods.
+# AllowedMethods: alias_method, public, protected, private
+Layout/EmptyLinesAroundAttributeAccessor:
+  Exclude:
+    - 'app/models/hiera_data.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: empty_lines, no_empty_lines
+Layout/EmptyLinesAroundBlockBody:
+  Exclude:
+    - 'db/schema.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: empty_lines, empty_lines_except_namespace, empty_lines_special, no_empty_lines, beginning_only, ending_only
+Layout/EmptyLinesAroundClassBody:
+  Exclude:
+    - 'test/controllers/sessions_controller_test.rb'
+    - 'test/integration/required_authentication_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: empty_lines, empty_lines_except_namespace, empty_lines_special, no_empty_lines
+Layout/EmptyLinesAroundModuleBody:
+  Exclude:
+    - 'app/models/hiera_data/interpolation.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: AllowForAlignment, AllowBeforeTrailingComments, ForceEqualSignAlignment.
+Layout/ExtraSpacing:
+  Exclude:
+    - 'test/models/hiera_data_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: special_inside_parentheses, consistent, align_brackets
+Layout/FirstArrayElementIndentation:
+  Exclude:
+    - 'test/models/hiera_data_test.rb'
+
+# Offense count: 13
+# Cop supports --auto-correct.
+# Configuration parameters: AllowMultipleStyles, EnforcedHashRocketStyle, EnforcedColonStyle, EnforcedLastArgumentHashStyle.
+# SupportedHashRocketStyles: key, separator, table
+# SupportedColonStyles: key, separator, table
+# SupportedLastArgumentHashStyles: always_inspect, always_ignore, ignore_implicit, ignore_explicit
+Layout/HashAlignment:
+  Exclude:
+    - 'app/models/user.rb'
+    - 'test/models/key_test.rb'
+    - 'test/models/node_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Layout/HeredocIndentation:
+  Exclude:
+    - 'test/models/hiera_data/yaml_file_test.rb'
+
+# Offense count: 4
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: normal, indented_internal_methods
+Layout/IndentationConsistency:
+  Exclude:
+    - 'app/controllers/users_controller.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+
+# Offense count: 4
+# Cop supports --auto-correct.
+# Configuration parameters: Width, IgnoredPatterns.
+Layout/IndentationWidth:
+  Exclude:
+    - 'app/controllers/users_controller.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: symmetrical, new_line, same_line
+Layout/MultilineArrayBraceLayout:
+  Exclude:
+    - 'app/services/puppet_db_client.rb'
+
+# Offense count: 8
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: aligned, indented, indented_relative_to_receiver
+Layout/MultilineMethodCallIndentation:
+  Exclude:
+    - 'app/models/hiera_data/data_file.rb'
+    - 'app/models/hiera_data/hierarchy.rb'
+    - 'app/models/key.rb'
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, IndentationWidth.
+# SupportedStyles: aligned, indented
+Layout/MultilineOperationIndentation:
+  Exclude:
+    - 'bin/bundle'
+
+# Offense count: 9
+# Cop supports --auto-correct.
+Layout/SpaceAfterComma:
+  Exclude:
+    - 'config/environments/development.rb'
+    - 'config/environments/test.rb'
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 13
+# Cop supports --auto-correct.
+# Configuration parameters: AllowForAlignment, EnforcedStyleForExponentOperator.
+# SupportedStylesForExponentOperator: space, no_space
+Layout/SpaceAroundOperators:
+  Exclude:
+    - 'app/models/hiera_data/yaml_file.rb'
+    - 'test/models/hiera_data/data_file_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/models/hiera_data_test.rb'
+    - 'test/models/node_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Layout/SpaceBeforeComma:
+  Exclude:
+    - 'app/models/node.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, EnforcedStyleForEmptyBrackets.
+# SupportedStyles: space, no_space, compact
+# SupportedStylesForEmptyBrackets: space, no_space
+Layout/SpaceInsideArrayLiteralBrackets:
+  Exclude:
+    - 'config/environments/production.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, EnforcedStyleForEmptyBraces, SpaceBeforeBlockParameters.
+# SupportedStyles: space, no_space
+# SupportedStylesForEmptyBraces: space, no_space
+Layout/SpaceInsideBlockBraces:
+  Exclude:
+    - 'app/models/hiera_data/interpolation.rb'
+
+# Offense count: 67
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, EnforcedStyleForEmptyBraces.
+# SupportedStyles: space, no_space, compact
+# SupportedStylesForEmptyBraces: space, no_space
+Layout/SpaceInsideHashLiteralBraces:
+  Exclude:
+    - 'config/routes.rb'
+    - 'test/models/hiera_data/data_file_test.rb'
+    - 'test/models/hiera_data/hierarchy_test.rb'
+    - 'test/models/hiera_data/interpolation_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/models/hiera_data_test.rb'
+    - 'test/models/key_test.rb'
+    - 'test/models/node_test.rb'
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowInHeredoc.
+Layout/TrailingWhitespace:
+  Exclude:
+    - 'config/initializers/friendly_id.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+Lint/AmbiguousRegexpLiteral:
+  Exclude:
+    - 'test/models/hiera_data_test.rb'
+
+# Offense count: 2
+# Configuration parameters: AllowSafeAssignment.
+Lint/AssignmentInCondition:
+  Exclude:
+    - 'app/models/hiera_data/data_file.rb'
+    - 'app/models/hiera_data/git_repo.rb'
+
+# Offense count: 5
+# Configuration parameters: AllowedMethods.
+# AllowedMethods: enums
+Lint/ConstantDefinitionInBlock:
+  Exclude:
+    - 'config/environments/development.rb'
+    - 'config/environments/production.rb'
+    - 'config/environments/test.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+Lint/DeprecatedClassMethods:
+  Exclude:
+    - 'app/models/hiera_data/git_repo.rb'
+
+# Offense count: 1
+# Configuration parameters: AllowComments.
+Lint/EmptyFile:
+  Exclude:
+    - 'config/initializers/cancan.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+Lint/ScriptPermission:
+  Exclude:
+    - 'test/fixtures/files/puppet/environments/eyaml/generate_eyaml_entries.rb'
+    - 'test/fixtures/files/puppet/generate_nodes.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: IgnoreEmptyBlocks, AllowUnusedKeywordArguments.
+Lint/UnusedBlockArgument:
+  Exclude:
+    - 'app/models/key.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowUnusedKeywordArguments, IgnoreEmptyMethods, IgnoreNotImplementedMethods.
+Lint/UnusedMethodArgument:
+  Exclude:
+    - 'test/test_helper.rb'
+
+# Offense count: 3
+# Configuration parameters: IgnoredMethods, CountRepeatedAttributes.
+Metrics/AbcSize:
+  Max: 27
+
+# Offense count: 1
+# Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.
+# IgnoredMethods: refine
+Metrics/BlockLength:
+  Max: 27
+
+# Offense count: 1
+# Configuration parameters: CountComments, CountAsOne.
+Metrics/ClassLength:
+  Max: 109
+
+# Offense count: 2
+# Configuration parameters: IgnoredMethods.
+Metrics/CyclomaticComplexity:
+  Max: 9
+
+# Offense count: 16
+# Configuration parameters: CountComments, CountAsOne, ExcludedMethods, IgnoredMethods.
+Metrics/MethodLength:
+  Max: 22
+
+# Offense count: 2
+# Configuration parameters: CountKeywordArgs, MaxOptionalParameters.
+Metrics/ParameterLists:
+  Max: 8
+
+# Offense count: 1
+# Configuration parameters: IgnoredMethods.
+Metrics/PerceivedComplexity:
+  Max: 9
+
+# Offense count: 1
+# Configuration parameters: NamePrefix, ForbiddenPrefixes, AllowedMethods, MethodDefinitionMacros.
+# NamePrefix: is_, has_, have_
+# ForbiddenPrefixes: is_, has_, have_
+# AllowedMethods: is_a?
+# MethodDefinitionMacros: define_method, define_singleton_method
+Naming/PredicateName:
+  Exclude:
+    - 'app/models/hiera_data/yaml_file.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: PreferredName.
+Naming/RescuedExceptionsVariableName:
+  Exclude:
+    - 'app/models/hiera_data/config.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: NilOrEmpty, NotPresent, UnlessPresent.
+Rails/Blank:
+  Exclude:
+    - 'app/models/ability.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: Whitelist, AllowedMethods, AllowedReceivers.
+# Whitelist: find_by_sql
+# AllowedMethods: find_by_sql
+# AllowedReceivers: Gem::Specification
+Rails/DynamicFindBy:
+  Exclude:
+    - 'app/controllers/sessions_controller.rb'
+
+# Offense count: 9
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: slashes, arguments
+Rails/FilePath:
+  Exclude:
+    - 'config/environments/development.rb'
+    - 'test/models/hiera_data/data_file_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/models/hiera_data_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: NotNilAndNotEmpty, NotBlank, UnlessBlank.
+Rails/Present:
+  Exclude:
+    - 'bin/bundle'
+
+# Offense count: 9
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, Include.
+# SupportedStyles: assert_not, refute
+# Include: **/test/**/*
+Rails/RefuteMethods:
+  Exclude:
+    - 'test/models/hiera_data/hierarchy_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/models/hierarchy_test.rb'
+    - 'test/models/user_test.rb'
+
+# Offense count: 5
+# Configuration parameters: Include.
+# Include: db/**/*.rb
+Rails/ReversibleMigration:
+  Exclude:
+    - 'db/migrate/20210326144242_drop_puppet_tables.rb'
+
+# Offense count: 11
+# Cop supports --auto-correct.
+Security/YAMLLoad:
+  Exclude:
+    - 'app/models/hiera_data/config.rb'
+    - 'app/models/hiera_data/yaml_file.rb'
+    - 'app/models/key.rb'
+    - 'test/models/hiera_data/data_file_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/models/hiera_data_test.rb'
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, ProceduralMethods, FunctionalMethods, IgnoredMethods, AllowBracesOnProceduralOneLiners, BracesRequiredMethods.
+# SupportedStyles: line_count_based, semantic, braces_for_chaining, always_braces
+# ProceduralMethods: benchmark, bm, bmbm, create, each_with_object, measure, new, realtime, tap, with_object
+# FunctionalMethods: let, let!, subject, watch
+# IgnoredMethods: lambda, proc, it
+Style/BlockDelimiters:
+  Exclude:
+    - 'test/fixtures/files/puppet/environments/eyaml/generate_eyaml_entries.rb'
+    - 'test/fixtures/files/puppet/generate_nodes.rb'
+
+# Offense count: 16
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: nested, compact
+Style/ClassAndModuleChildren:
+  Exclude:
+    - 'test/channels/application_cable/connection_test.rb'
+    - 'test/models/hiera_data/config_test.rb'
+    - 'test/models/hiera_data/data_file_test.rb'
+    - 'test/models/hiera_data/git_repo_test.rb'
+    - 'test/models/hiera_data/hierarchy_test.rb'
+    - 'test/models/hiera_data/interpolation_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+    - 'test/test_helper.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, AllowInnerBackticks.
+# SupportedStyles: backticks, percent_x, mixed
+Style/CommandLiteral:
+  Exclude:
+    - 'test/fixtures/files/puppet/environments/eyaml/generate_eyaml_entries.rb'
+
+# Offense count: 45
+# Configuration parameters: AllowedConstants.
+Style/Documentation:
+  Enabled: false
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/ExpandPathArguments:
+  Exclude:
+    - 'bin/bundle'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/FileWrite:
+  Exclude:
+    - 'test/fixtures/files/puppet/generate_nodes.rb'
+
+# Offense count: 1
+# Configuration parameters: MaxUnannotatedPlaceholdersAllowed, IgnoredMethods.
+# SupportedStyles: annotated, template, unannotated
+Style/FormatStringToken:
+  EnforcedStyle: template
+
+# Offense count: 109
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: always, always_true, never
+Style/FrozenStringLiteralComment:
+  Enabled: false
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/GlobalStdStream:
+  Exclude:
+    - 'config/environments/production.rb'
+
+# Offense count: 7
+# Configuration parameters: MinBodyLength.
+Style/GuardClause:
+  Exclude:
+    - 'app/controllers/application_controller.rb'
+    - 'app/controllers/page_controller.rb'
+    - 'app/controllers/sessions_controller.rb'
+    - 'app/models/hiera_data/data_file.rb'
+    - 'app/models/hiera_data/hierarchy.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowSplatArgument.
+Style/HashConversion:
+  Exclude:
+    - 'test/support/fake_puppet_db.rb'
+
+# Offense count: 1
+# Configuration parameters: MinBranchesCount.
+Style/HashLikeCase:
+  Exclude:
+    - 'app/helpers/application_helper.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: AllowIfModifier.
+Style/IfInsideElse:
+  Exclude:
+    - 'app/controllers/users_controller.rb'
+
+# Offense count: 10
+# Cop supports --auto-correct.
+Style/IfUnlessModifier:
+  Exclude:
+    - 'app/controllers/application_controller.rb'
+    - 'app/controllers/page_controller.rb'
+    - 'app/controllers/sessions_controller.rb'
+    - 'app/controllers/users_controller.rb'
+    - 'app/models/hiera_data/config.rb'
+    - 'app/models/hiera_data/hierarchy.rb'
+    - 'bin/bundle'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: literals, strict
+Style/MutableConstant:
+  Exclude:
+    - 'app/models/value.rb'
+
+# Offense count: 5
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedOctalStyle.
+# SupportedOctalStyles: zero_with_o, zero_only
+Style/NumericLiteralPrefix:
+  Exclude:
+    - 'app/models/hiera_data/yaml_file.rb'
+    - 'test/models/hiera_data/hierarchy_test.rb'
+    - 'test/models/hiera_data/yaml_file_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: MinDigits, Strict, AllowedNumbers.
+Style/NumericLiterals:
+  Exclude:
+    - 'db/schema.rb'
+
+# Offense count: 7
+# Cop supports --auto-correct.
+# Configuration parameters: PreferredDelimiters.
+Style/PercentLiteralDelimiters:
+  Exclude:
+    - 'app/models/hiera_data/hierarchy.rb'
+    - 'config/initializers/friendly_id.rb'
+    - 'test/models/environment_test.rb'
+    - 'test/models/hiera_data/hierarchy_test.rb'
+    - 'test/models/key_test.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/PerlBackrefs:
+  Exclude:
+    - 'bin/bundle'
+
+# Offense count: 5
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: short, verbose
+Style/PreferredHashMethods:
+  Exclude:
+    - 'app/models/hiera_data/data_file.rb'
+    - 'app/models/hiera_data/hierarchy.rb'
+    - 'app/models/hiera_data/yaml_file.rb'
+
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, AllowedCompactTypes.
+# SupportedStyles: compact, exploded
+Style/RaiseArgs:
+  Exclude:
+    - 'app/models/hiera_data.rb'
+    - 'app/models/hiera_data/git_repo.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/RedundantBegin:
+  Exclude:
+    - 'test/test_helper.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/RedundantCondition:
+  Exclude:
+    - 'app/models/hiera_data/yaml_file.rb'
+
+# Offense count: 2
+# Cop supports --auto-correct.
+# Configuration parameters: SafeForConstants.
+Style/RedundantFetchBlock:
+  Exclude:
+    - 'config/puma.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/RedundantSelf:
+  Exclude:
+    - 'app/models/user.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, AllowInnerSlashes.
+# SupportedStyles: slashes, percent_r, mixed
+Style/RegexpLiteral:
+  Exclude:
+    - 'config/routes.rb'
+
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: implicit, explicit
+Style/RescueStandardError:
+  Exclude:
+    - 'app/models/hiera_data/config.rb'
+    - 'app/services/puppet_db_client.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: ConvertCodeThatCanStartToReturnNil, AllowedMethods.
+# AllowedMethods: present?, blank?, presence, try, try!
+Style/SafeNavigation:
+  Exclude:
+    - 'app/controllers/sessions_controller.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+Style/SingleArgumentDig:
+  Exclude:
+    - 'app/services/puppet_db_client.rb'
+
+# Offense count: 1
+# Cop supports --auto-correct.
+# Configuration parameters: RequireEnglish.
+# SupportedStyles: use_perl_names, use_english_names
+Style/SpecialGlobalVars:
+  EnforcedStyle: use_perl_names
+
+# Offense count: 2
+# Cop supports --auto-correct.
+Style/StderrPuts:
+  Exclude:
+    - 'bin/yarn'
+
+# Offense count: 785
+# Cop supports --auto-correct.
+# Configuration parameters: EnforcedStyle, ConsistentQuotesInMultiline.
+# SupportedStyles: single_quotes, double_quotes
+Style/StringLiterals:
+  Enabled: false
+
+# Offense count: 9
+# Cop supports --auto-correct.
+# Configuration parameters: MinSize.
+# SupportedStyles: percent, brackets
+Style/SymbolArray:
+  EnforcedStyle: brackets
+
+# Offense count: 3
+# Cop supports --auto-correct.
+# Configuration parameters: WordRegex.
+# SupportedStyles: percent, brackets
+Style/WordArray:
+  EnforcedStyle: percent
+  MinSize: 3
+
+# Offense count: 2
+# Cop supports --auto-correct.
+Style/ZeroLengthPredicate:
+  Exclude:
+    - 'test/fixtures/files/puppet/environments/eyaml/generate_eyaml_entries.rb'
+    - 'test/fixtures/files/puppet/generate_nodes.rb'
+
+# Offense count: 25
+# Cop supports --auto-correct.
+# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
+# URISchemes: http, https
+Layout/LineLength:
+  Max: 3835
diff --git a/Gemfile b/Gemfile
index 01a51714..2d693f01 100644
--- a/Gemfile
+++ b/Gemfile
@@ -55,6 +55,12 @@ group :test do
   gem 'webdrivers'
 end
 
+group :linter do
+  gem 'rubocop'
+  gem 'rubocop-rails'
+  gem 'rubocop-rake'
+end
+
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
 gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
 
diff --git a/Gemfile.lock b/Gemfile.lock
index bc313706..bbb8b151 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -63,6 +63,7 @@ GEM
       zeitwerk (~> 2.3)
     addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
+    ast (2.4.2)
     bcrypt (3.1.17)
     bindex (0.8.1)
     breadcrumbs_on_rails (4.1.0)
@@ -136,10 +137,26 @@ GEM
     nio4r (2.5.8)
     nokogiri (1.12.5-x86_64-darwin)
       racc (~> 1.4)
+    nokogiri (1.12.5-x86_64-linux)
+      racc (~> 1.4)
     optimist (3.0.1)
+    parallel (1.22.1)
+    parser (3.1.1.0)
+      ast (~> 2.4.1)
     public_suffix (4.0.6)
     puma (5.6.4)
       nio4r (~> 2.0)
+    puppet (7.15.0)
+      concurrent-ruby (~> 1.0)
+      deep_merge (~> 1.0)
+      facter (> 2.0.1, < 5)
+      fast_gettext (>= 1.1, < 3)
+      hiera (>= 3.2.1, < 4)
+      locale (~> 2.1)
+      multi_json (~> 1.10)
+      puppet-resource_api (~> 1.5)
+      scanf (~> 1.0)
+      semantic_puppet (~> 1.0)
     puppet (7.15.0-universal-darwin)
       CFPropertyList (~> 2.2)
       concurrent-ruby (~> 1.0)
@@ -188,12 +205,32 @@ GEM
       method_source
       rake (>= 12.2)
       thor (~> 1.0)
+    rainbow (3.1.1)
     rake (13.0.6)
     rb-fsevent (0.11.1)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rchardet (1.8.0)
     regexp_parser (2.2.1)
+    rexml (3.2.5)
+    rubocop (1.26.1)
+      parallel (~> 1.10)
+      parser (>= 3.1.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml
+      rubocop-ast (>= 1.16.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 1.4.0, < 3.0)
+    rubocop-ast (1.16.0)
+      parser (>= 3.1.1.0)
+    rubocop-rails (2.13.2)
+      activesupport (>= 4.2.0)
+      rack (>= 1.1)
+      rubocop (>= 1.7.0, < 2.0)
+    rubocop-rake (0.6.0)
+      rubocop (~> 1.0)
+    ruby-progressbar (1.11.0)
     rubyzip (2.3.2)
     sass-rails (6.0.0)
       sassc-rails (~> 2.1, >= 2.1.1)
@@ -232,6 +269,7 @@ GEM
     turbolinks-source (5.2.0)
     tzinfo (2.0.4)
       concurrent-ruby (~> 1.0)
+    unicode-display_width (2.1.0)
     web-console (4.2.0)
       actionview (>= 6.0.0)
       activemodel (>= 6.0.0)
@@ -255,6 +293,7 @@ GEM
 
 PLATFORMS
   x86_64-darwin-21
+  x86_64-linux
 
 DEPENDENCIES
   bcrypt (~> 3.1.7)
@@ -273,6 +312,9 @@ DEPENDENCIES
   puppet
   puppetdb-ruby
   rails (~> 6.1.5, >= 6.1.0.0)
+  rubocop
+  rubocop-rails
+  rubocop-rake
   sass-rails (>= 6)
   selenium-webdriver
   simplecov
diff --git a/Rakefile b/Rakefile
index e85f9139..10249c3c 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,6 +1,18 @@
 # Add your own tasks in files placed in lib/tasks ending in .rake,
 # for example lib/tasks/capistrano.rake, and they will automatically be available to Rake.
 
-require_relative 'config/application'
+require 'rubocop/rake_task'
+RuboCop::RakeTask.new(:rubocop) do |task|
+  # These make the rubocop experience maybe slightly less terrible
+  task.options = ['-D', '-S', '-E']
 
-Rails.application.load_tasks
+  # Use Rubocop's Github Actions formatter if possible
+  task.formatters << 'github' if ENV['GITHUB_ACTIONS'] == 'true'
+end
+# check if the rails configuration exists and load the tasks
+if File.file?('config/hdm.yml')
+  require_relative 'config/application'
+  Rails.application.load_tasks
+else
+  puts "Not loading Rails specific tasks because config/hdm.yml is missing!"
+end