diff --git a/.codeclimate.yml b/.codeclimate.yml
index b4ec9400e..9c9b4517a 100644
--- a/.codeclimate.yml
+++ b/.codeclimate.yml
@@ -30,7 +30,7 @@ plugins:
     channel: eslint-7
   rubocop:
     enabled: true
-    channel: rubocop-0-82
+    channel: rubocop-0-88
   sass-lint:
     enabled: true
 exclude_patterns:
diff --git a/.rubocop.yml b/.rubocop.yml
index 25e0fa940..14728bf0e 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -25,30 +25,68 @@ Layout/AccessModifierIndentation:
 Layout/EmptyLineAfterMagicComment:
   Enabled: false
 
+Layout/EmptyLineAfterGuardClause:
+  Enabled: false
+
+Layout/EmptyLinesAroundAttributeAccessor:
+  Enabled: true
+
+Layout/HashAlignment:
+  Enabled: false
+  # EnforcedHashRocketStyle: table
+  # EnforcedColonStyle: table
+
+Layout/SpaceAroundMethodCallOperator:
+  Enabled: true
+
 Layout/SpaceInsideHashLiteralBraces:
   EnforcedStyle: space
 
+Lint/DeprecatedOpenSSLConstant:
+  Enabled: true
+
+Lint/DuplicateElsifCondition:
+  Enabled: true
+
+Lint/MixedRegexpCaptureTypes:
+  Enabled: true
+
+Lint/RaiseException:
+  Enabled: true
+
+Lint/StructNewOverride:
+  Enabled: true
+
 Lint/UselessAccessModifier:
   ContextCreatingMethods:
     - class_methods
 
 Metrics/AbcSize:
   Max: 100
+  Exclude:
+    - 'lib/mastodon/*_cli.rb'
 
 Metrics/BlockLength:
-  Max: 35
+  Max: 55
   Exclude:
     - 'lib/tasks/**/*'
+    - 'lib/mastodon/*_cli.rb'
 
 Metrics/BlockNesting:
   Max: 3
+  Exclude:
+    - 'lib/mastodon/*_cli.rb'
 
 Metrics/ClassLength:
   CountComments: false
-  Max: 300
+  Max: 400
+  Exclude:
+    - 'lib/mastodon/*_cli.rb'
 
 Metrics/CyclomaticComplexity:
   Max: 25
+  Exclude:
+    - 'lib/mastodon/*_cli.rb'
 
 Layout/LineLength:
   AllowURI: true
@@ -56,7 +94,9 @@ Layout/LineLength:
 
 Metrics/MethodLength:
   CountComments: false
-  Max: 55
+  Max: 65
+  Exclude:
+    - 'lib/mastodon/*_cli.rb'
 
 Metrics/ModuleLength:
   CountComments: false
@@ -67,24 +107,29 @@ Metrics/ParameterLists:
   CountKeywordArgs: true
 
 Metrics/PerceivedComplexity:
-  Max: 20
+  Max: 25
 
 Naming/MemoizedInstanceVariableName:
   Enabled: false
 
+Naming/MethodParameterName:
+  Enabled: true
+
 Rails:
   Enabled: true
 
-Rails/EnumHash:
+Rails/ApplicationController:
   Enabled: false
+  Exclude:
+    - 'app/controllers/well_known/**/*.rb'
 
-Rails/HasAndBelongsToMany:
+Rails/BelongsTo:
   Enabled: false
 
-Rails/SkipsModelValidations:
+Rails/ContentTag:
   Enabled: false
 
-Rails/HttpStatus:
+Rails/EnumHash:
   Enabled: false
 
 Rails/Exit:
@@ -92,9 +137,60 @@ Rails/Exit:
     - 'lib/mastodon/*'
     - 'lib/cli.rb'
 
+Rails/FilePath:
+  Enabled: false
+
+Rails/HasAndBelongsToMany:
+  Enabled: false
+
+Rails/HasManyOrHasOneDependent:
+  Enabled: false
+
 Rails/HelperInstanceVariable:
   Enabled: false
 
+Rails/HttpStatus:
+  Enabled: false
+
+Rails/IndexBy:
+  Enabled: false
+
+Rails/InverseOf:
+  Enabled: false
+
+Rails/LexicallyScopedActionFilter:
+  Enabled: false
+
+Rails/OutputSafety:
+  Enabled: true
+
+Rails/RakeEnvironment:
+  Enabled: false
+
+Rails/RedundantForeignKey:
+  Enabled: false
+
+Rails/SkipsModelValidations:
+  Enabled: false
+
+Rails/UniqueValidationWithoutIndex:
+  Enabled: false
+
+Style/AccessorGrouping:
+  Enabled: true
+
+Style/AccessModifierDeclarations:
+  Enabled: false
+
+Style/ArrayCoercion:
+  Enabled: true
+
+Style/BisectedAttrAccessor:
+  Enabled: true
+
+Style/CaseLikeIf:
+  Enabled: false
+
 Style/ClassAndModuleChildren:
   Enabled: false
 
@@ -109,6 +205,15 @@ Style/Documentation:
 Style/DoubleNegation:
   Enabled: true
 
+Style/ExpandPathArguments:
+  Enabled: false
+
+Style/ExponentialNotation:
+  Enabled: true
+
+Style/FormatString:
+  Enabled: false
+
 Style/FormatStringToken:
   Enabled: false
 
@@ -118,9 +223,33 @@ Style/FrozenStringLiteralComment:
 Style/GuardClause:
   Enabled: false
 
+Style/HashAsLastArrayItem:
+  Enabled: false
+
+Style/HashEachMethods:
+  Enabled: true
+
+Style/HashLikeCase:
+  Enabled: true
+
+Style/HashTransformKeys:
+  Enabled: true
+
+Style/HashTransformValues:
+  Enabled: false
+
+Style/IfUnlessModifier:
+  Enabled: false
+
+Style/InverseMethods:
+  Enabled: false
+
 Style/Lambda:
   Enabled: false
 
+Style/MutableConstant:
+  Enabled: false
+
 Style/PercentLiteralDelimiters:
   PreferredDelimiters:
     '%i': '()'
@@ -129,9 +258,36 @@ Style/PercentLiteralDelimiters:
 Style/PerlBackrefs:
   AutoCorrect: false
 
+Style/RedundantAssignment:
+  Enabled: false
+
+Style/RedundantFetchBlock:
+  Enabled: true
+
+Style/RedundantFileExtensionInRequire:
+  Enabled: true
+
+Style/RedundantRegexpCharacterClass:
+  Enabled: false
+
+Style/RedundantRegexpEscape:
+  Enabled: false
+
+Style/RedundantReturn:
+  Enabled: true
+
 Style/RegexpLiteral:
   Enabled: false
 
+Style/RescueStandardError:
+  Enabled: false
+
+Style/SignalException:
+  Enabled: false
+
+Style/SlicingWithRange:
+  Enabled: true
+
 Style/SymbolArray:
   Enabled: false
 
@@ -140,3 +296,6 @@ Style/TrailingCommaInArrayLiteral:
 
 Style/TrailingCommaInHashLiteral:
   EnforcedStyleForMultiline: 'comma'
+
+Style/UnpackFirst:
+  Enabled: false
diff --git a/Gemfile b/Gemfile
index 3f53e3f63..6a683d586 100644
--- a/Gemfile
+++ b/Gemfile
@@ -140,7 +140,7 @@ group :development do
   gem 'letter_opener', '~> 1.7'
   gem 'letter_opener_web', '~> 1.4'
   gem 'memory_profiler'
-  gem 'rubocop', '~> 0.86', require: false
+  gem 'rubocop', '~> 0.88', require: false
   gem 'rubocop-rails', '~> 2.6', require: false
   gem 'brakeman', '~> 4.9', require: false
   gem 'bundler-audit', '~> 0.7', require: false
diff --git a/Gemfile.lock b/Gemfile.lock
index 4157e1269..1e289c30a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -535,13 +535,13 @@ GEM
     rspec-support (3.9.3)
     rspec_junit_formatter (0.4.1)
       rspec-core (>= 2, < 4, != 2.12.0)
-    rubocop (0.86.0)
+    rubocop (0.88.0)
       parallel (~> 1.10)
-      parser (>= 2.7.0.1)
+      parser (>= 2.7.1.1)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.7)
       rexml
-      rubocop-ast (>= 0.0.3, < 1.0)
+      rubocop-ast (>= 0.1.0, < 1.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 2.0)
     rubocop-ast (0.3.0)
@@ -778,7 +778,7 @@ DEPENDENCIES
   rspec-rails (~> 4.0)
   rspec-sidekiq (~> 3.1)
   rspec_junit_formatter (~> 0.4)
-  rubocop (~> 0.86)
+  rubocop (~> 0.88)
   rubocop-rails (~> 2.6)
   ruby-progressbar (~> 1.10)
   sanitize (~> 5.2)
diff --git a/app/controllers/api/base_controller.rb b/app/controllers/api/base_controller.rb
index 045e7dd26..467225547 100644
--- a/app/controllers/api/base_controller.rb
+++ b/app/controllers/api/base_controller.rb
@@ -71,6 +71,7 @@ class Api::BaseController < ApplicationController
 
   def limit_param(default_limit)
     return default_limit unless params[:limit]
+
     [params[:limit].to_i.abs, default_limit * 2].min
   end
 
diff --git a/app/controllers/concerns/challengable_concern.rb b/app/controllers/concerns/challengable_concern.rb
index b29d90b3c..2995a25e0 100644
--- a/app/controllers/concerns/challengable_concern.rb
+++ b/app/controllers/concerns/challengable_concern.rb
@@ -32,7 +32,6 @@ module ChallengableConcern
     if params.key?(:form_challenge)
       if challenge_passed?
         session[:challenge_passed_at] = Time.now.utc
-        return
       else
         flash.now[:alert] = I18n.t('challenge.invalid_password')
         render_challenge
diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 18f549de9..f69c62ec2 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -131,7 +131,7 @@ module SignatureVerification
   end
 
   def verify_signature(account, signature, compare_signed_string)
-    if account.keypair.public_key.verify(OpenSSL::Digest::SHA256.new, signature, compare_signed_string)
+    if account.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), signature, compare_signed_string)
       @signed_request_account = account
       @signed_request_account
     end
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 716df0bac..5512a9543 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -162,6 +162,8 @@ module ApplicationHelper
     end
 
     json = ActiveModelSerializers::SerializableResource.new(InitialStatePresenter.new(state_params), serializer: InitialStateSerializer).to_json
+    # rubocop:disable Rails/OutputSafety
     content_tag(:script, json_escape(json).html_safe, id: 'initial-state', type: 'application/json')
+    # rubocop:enable Rails/OutputSafety
   end
 end
diff --git a/app/lib/activitypub/linked_data_signature.rb b/app/lib/activitypub/linked_data_signature.rb
index f52a8f406..e853a970e 100644
--- a/app/lib/activitypub/linked_data_signature.rb
+++ b/app/lib/activitypub/linked_data_signature.rb
@@ -27,7 +27,7 @@ class ActivityPub::LinkedDataSignature
     document_hash  = hash(@json.without('signature'))
     to_be_verified = options_hash + document_hash
 
-    if creator.keypair.public_key.verify(OpenSSL::Digest::SHA256.new, Base64.decode64(signature), to_be_verified)
+    if creator.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), Base64.decode64(signature), to_be_verified)
       creator
     end
   end
@@ -44,7 +44,7 @@ class ActivityPub::LinkedDataSignature
     to_be_signed  = options_hash + document_hash
     keypair       = sign_with.present? ? OpenSSL::PKey::RSA.new(sign_with) : creator.keypair
 
-    signature = Base64.strict_encode64(keypair.sign(OpenSSL::Digest::SHA256.new, to_be_signed))
+    signature = Base64.strict_encode64(keypair.sign(OpenSSL::Digest.new('SHA256'), to_be_signed))
 
     @json.merge('signature' => options.merge('signatureValue' => signature))
   end
diff --git a/app/lib/entity_cache.rb b/app/lib/entity_cache.rb
index afdbd70f2..89cbf8d2c 100644
--- a/app/lib/entity_cache.rb
+++ b/app/lib/entity_cache.rb
@@ -16,7 +16,7 @@ class EntityCache
   end
 
   def emoji(shortcodes, domain)
-    shortcodes   = [shortcodes] unless shortcodes.is_a?(Array)
+    shortcodes   = Array(shortcodes)
     cached       = Rails.cache.read_multi(*shortcodes.map { |shortcode| to_key(:emoji, shortcode, domain) })
     uncached_ids = []
 
diff --git a/app/lib/formatter.rb b/app/lib/formatter.rb
index e6f5d7a63..7f217ae9f 100644
--- a/app/lib/formatter.rb
+++ b/app/lib/formatter.rb
@@ -135,6 +135,7 @@ class Formatter
     end
   end
 
+  # rubocop:disable Metrics/BlockNesting
   def encode_custom_emojis(html, emojis, animate = false)
     return html if emojis.empty?
 
@@ -189,6 +190,7 @@ class Formatter
 
     html
   end
+  # rubocop:enable Metrics/BlockNesting
 
   def rewrite(text, entities)
     text = text.to_s
diff --git a/app/lib/request.rb b/app/lib/request.rb
index bcba1eebf..89fbeaf95 100644
--- a/app/lib/request.rb
+++ b/app/lib/request.rb
@@ -114,7 +114,7 @@ class Request
 
   def signature
     algorithm = 'rsa-sha256'
-    signature = Base64.strict_encode64(@keypair.sign(OpenSSL::Digest::SHA256.new, signed_string))
+    signature = Base64.strict_encode64(@keypair.sign(OpenSSL::Digest.new('SHA256'), signed_string))
 
     "keyId=\"#{key_id}\",algorithm=\"#{algorithm}\",headers=\"#{signed_headers.keys.join(' ').downcase}\",signature=\"#{signature}\""
   end
diff --git a/app/lib/sidekiq_error_handler.rb b/app/lib/sidekiq_error_handler.rb
index b07817d45..ab555b1be 100644
--- a/app/lib/sidekiq_error_handler.rb
+++ b/app/lib/sidekiq_error_handler.rb
@@ -17,8 +17,10 @@ class SidekiqErrorHandler
 
   private
 
+  # rubocop:disable Naming/MethodParameterName
   def limit_backtrace_and_raise(e)
     e.set_backtrace(e.backtrace.first(BACKTRACE_LIMIT))
     raise e
   end
+  # rubocop:enable Naming/MethodParameterName
 end
diff --git a/app/models/preview_card.rb b/app/models/preview_card.rb
index 235928260..a6ec839f8 100644
--- a/app/models/preview_card.rb
+++ b/app/models/preview_card.rb
@@ -72,6 +72,7 @@ class PreviewCard < ApplicationRecord
   class << self
     private
 
+    # rubocop:disable Naming/MethodParameterName
     def image_styles(f)
       styles = {
         original: {
@@ -85,6 +86,7 @@ class PreviewCard < ApplicationRecord
       styles[:original][:format] = 'jpg' if f.instance.image_content_type == 'image/gif'
       styles
     end
+    # rubocop:enable Naming/MethodParameterName
   end
 
   private
diff --git a/app/models/user.rb b/app/models/user.rb
index 7e3b37475..dbee08988 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -253,16 +253,16 @@ class User < ApplicationRecord
     @shows_application ||= settings.show_application
   end
 
+  # rubocop:disable Naming/MethodParameterName
   def token_for_app(a)
     return nil if a.nil? || a.owner != self
-    Doorkeeper::AccessToken
-      .find_or_create_by(application_id: a.id, resource_owner_id: id) do |t|
-
+    Doorkeeper::AccessToken.find_or_create_by(application_id: a.id, resource_owner_id: id) do |t|
       t.scopes = a.scopes
       t.expires_in = Doorkeeper.configuration.access_token_expires_in
       t.use_refresh_token = Doorkeeper.configuration.refresh_token_enabled?
     end
   end
+  # rubocop:enable Naming/MethodParameterName
 
   def activate_session(request)
     session_activations.activate(session_id: SecureRandom.hex,
@@ -413,7 +413,7 @@ class User < ApplicationRecord
   end
 
   def notify_staff_about_pending_account!
-    User.staff.includes(:account).each do |u|
+    User.staff.includes(:account).find_each do |u|
       next unless u.allows_pending_account_emails?
       AdminMailer.new_pending_account(u.account, self).deliver_later
     end
diff --git a/app/services/fetch_link_card_service.rb b/app/services/fetch_link_card_service.rb
index beab449b2..7efa31054 100644
--- a/app/services/fetch_link_card_service.rb
+++ b/app/services/fetch_link_card_service.rb
@@ -78,6 +78,7 @@ class FetchLinkCardService < BaseService
     uri.host.blank? || TagManager.instance.local_url?(uri.to_s) || !%w(http https).include?(uri.scheme)
   end
 
+  # rubocop:disable Naming/MethodParameterName
   def mention_link?(a)
     @status.mentions.any? do |mention|
       a['href'] == ActivityPub::TagManager.instance.url_for(mention.account)
@@ -88,6 +89,7 @@ class FetchLinkCardService < BaseService
     # Avoid links for hashtags and mentions (microformats)
     a['rel']&.include?('tag') || a['class']&.match?(/u-url|h-card/) || mention_link?(a)
   end
+  # rubocop:enable Naming/MethodParameterName
 
   def attempt_oembed
     service         = FetchOEmbedService.new
diff --git a/app/services/notify_service.rb b/app/services/notify_service.rb
index 9364a6ae8..abd676494 100644
--- a/app/services/notify_service.rb
+++ b/app/services/notify_service.rb
@@ -13,7 +13,9 @@ class NotifyService < BaseService
     push_to_conversation! if direct_message?
     send_email! if email_enabled?
   rescue ActiveRecord::RecordInvalid
+    # rubocop:disable Style/RedundantReturn
     return
+    # rubocop:enable Style/RedundantReturn
   end
 
   private
diff --git a/app/services/update_account_service.rb b/app/services/update_account_service.rb
index 666db5c71..77f794e17 100644
--- a/app/services/update_account_service.rb
+++ b/app/services/update_account_service.rb
@@ -12,8 +12,8 @@ class UpdateAccountService < BaseService
       check_links(account)
       process_hashtags(account)
     end
-  rescue Mastodon::DimensionsValidationError, Mastodon::StreamValidationError => de
-    account.errors.add(:avatar, de.message)
+  rescue Mastodon::DimensionsValidationError, Mastodon::StreamValidationError => e
+    account.errors.add(:avatar, e.message)
     false
   end
 
diff --git a/lib/mastodon/redis_config.rb b/lib/mastodon/redis_config.rb
index e9db9122f..c3c8ff800 100644
--- a/lib/mastodon/redis_config.rb
+++ b/lib/mastodon/redis_config.rb
@@ -23,7 +23,7 @@ end
 setup_redis_env_url
 setup_redis_env_url(:cache, false)
 
-namespace       = ENV.fetch('REDIS_NAMESPACE') { nil }
+namespace       = ENV.fetch('REDIS_NAMESPACE', nil)
 cache_namespace = namespace ? namespace + '_cache' : 'cache'
 
 REDIS_CACHE_PARAMS = {
diff --git a/lib/mastodon/version.rb b/lib/mastodon/version.rb
index 7aa6cb2c7..7b940d1f8 100644
--- a/lib/mastodon/version.rb
+++ b/lib/mastodon/version.rb
@@ -33,16 +33,16 @@ module Mastodon
     end
 
     def repository
-      ENV.fetch('GITHUB_REPOSITORY') { 'tootsuite/mastodon' }
+      ENV.fetch('GITHUB_REPOSITORY', 'tootsuite/mastodon')
     end
 
     def source_base_url
-      ENV.fetch('SOURCE_BASE_URL') { "https://github.com/#{repository}" }
+      ENV.fetch('SOURCE_BASE_URL', "https://github.com/#{repository}")
     end
 
     # specify git tag or commit hash here
     def source_tag
-      ENV.fetch('SOURCE_TAG') { nil }
+      ENV.fetch('SOURCE_TAG', nil)
     end
 
     def source_url
diff --git a/lib/paperclip/color_extractor.rb b/lib/paperclip/color_extractor.rb
index c8bb771a0..f850dc067 100644
--- a/lib/paperclip/color_extractor.rb
+++ b/lib/paperclip/color_extractor.rb
@@ -89,7 +89,7 @@ module Paperclip
       end
     end
 
-    # rubocop:disable Style/MethodParameterName
+    # rubocop:disable Naming/MethodParameterName
     def rgb_to_hsl(r, g, b)
       r /= 255.0
       g /= 255.0
@@ -156,7 +156,7 @@ module Paperclip
 
       [(r * 255).round, (g * 255).round, (b * 255).round]
     end
-    # rubocop:enable Style/MethodParameterName
+    # rubocop:enable Naming/MethodParameterName
 
     def lighten_or_darken(color, by)
       hue, saturation, light = rgb_to_hsl(color.r, color.g, color.b)