diff --git a/spec/ameba/ast/scope_spec.cr b/spec/ameba/ast/scope_spec.cr
index c3033a6e..f7f080fe 100644
--- a/spec/ameba/ast/scope_spec.cr
+++ b/spec/ameba/ast/scope_spec.cr
@@ -191,7 +191,7 @@ module Ameba::AST
     it "returns true if node is nested to Crystal::Macro" do
       nodes = as_nodes %(
         macro included
-          {{@type.each do |type| a = type end}}
+          {{ @type.each do |type| a = type end }}
         end
       )
       outer_scope = Scope.new nodes.macro_nodes.first
diff --git a/spec/ameba/config_spec.cr b/spec/ameba/config_spec.cr
index 98ecb851..86b111eb 100644
--- a/spec/ameba/config_spec.cr
+++ b/spec/ameba/config_spec.cr
@@ -40,7 +40,9 @@ module Ameba
           ---
           Globs: 100
           CONFIG
-        expect_raises(Exception, "incorrect 'Globs' section in a config file") { Config.new(yml) }
+        expect_raises(Exception, "Incorrect 'Globs' section in a config file") do
+          Config.new(yml)
+        end
       end
 
       it "initializes excluded as string" do
@@ -68,7 +70,9 @@ module Ameba
           ---
           Excluded: true
           CONFIG
-        expect_raises(Exception, "incorrect 'Excluded' section in a config file") { Config.new(yml) }
+        expect_raises(Exception, "Incorrect 'Excluded' section in a config file") do
+          Config.new(yml)
+        end
       end
     end
 
diff --git a/spec/ameba/rule/lint/shadowing_outer_local_var_spec.cr b/spec/ameba/rule/lint/shadowing_outer_local_var_spec.cr
index 5706841f..72340ebb 100644
--- a/spec/ameba/rule/lint/shadowing_outer_local_var_spec.cr
+++ b/spec/ameba/rule/lint/shadowing_outer_local_var_spec.cr
@@ -211,11 +211,13 @@ module Ameba::Rule::Lint
               end
 
               def bar
-                {{@type.instance_vars.map do |ivar|
+                {{
+                  @type.instance_vars.map do |ivar|
                     ivar.annotations(Name).each do |ann|
                       puts ann.args
                     end
-                  end}}
+                  end
+                }}
               end
             end
           end
diff --git a/spec/ameba/rule/lint/unused_argument_spec.cr b/spec/ameba/rule/lint/unused_argument_spec.cr
index 69bac6ea..d147384e 100644
--- a/spec/ameba/rule/lint/unused_argument_spec.cr
+++ b/spec/ameba/rule/lint/unused_argument_spec.cr
@@ -218,11 +218,11 @@ module Ameba::Rule::Lint
         s = Source.new %(
           record X do
             macro foo(a, b)
-              {{a}} + {{b}}
+              {{ a }} + {{ b }}
             end
 
             macro bar(a, b, c)
-              {{a}} + {{b}} + {{c}}
+              {{ a }} + {{ b }} + {{ c }}
             end
           end
         )
diff --git a/spec/ameba/rule/lint/useless_assign_spec.cr b/spec/ameba/rule/lint/useless_assign_spec.cr
index 25b15a22..5b7e06ac 100644
--- a/spec/ameba/rule/lint/useless_assign_spec.cr
+++ b/spec/ameba/rule/lint/useless_assign_spec.cr
@@ -949,7 +949,7 @@ module Ameba::Rule::Lint
           foo = 22
 
           {% for x in %w(foo) %}
-            add({{x.id}})
+            add({{ x.id }})
           {% end %}
         )
         subject.catch(s).should be_valid
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 9020b9b3..46ec4998 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -190,7 +190,7 @@ module Ameba
     def test(source, node : Crystal::ClassDef)
       return unless location = node.location
 
-      end_location = location.adjust(column_number: {{"class".size - 1}})
+      end_location = location.adjust(column_number: {{ "class".size - 1 }})
 
       issue_for(location, end_location, message: "class to module") do |corrector|
         corrector.replace(location, end_location, "module")
@@ -208,7 +208,7 @@ module Ameba
     def test(source, node : Crystal::ModuleDef)
       return unless location = node.location
 
-      end_location = location.adjust(column_number: {{"module".size - 1}})
+      end_location = location.adjust(column_number: {{ "module".size - 1 }})
 
       issue_for(location, end_location, message: "module to class") do |corrector|
         corrector.replace(location, end_location, "class")
@@ -265,12 +265,12 @@ module Ameba
     end
 
     {% for node in NODES %}
-      {{getter_name = node.stringify.split("::").last.underscore + "_nodes"}}
+      {{ getter_name = node.stringify.split("::").last.underscore + "_nodes" }}
 
-      getter {{getter_name.id}} = [] of {{node}}
+      getter {{ getter_name.id }} = [] of {{ node }}
 
-      def visit(node : {{node}})
-        {{getter_name.id}} << node
+      def visit(node : {{ node }})
+        {{ getter_name.id }} << node
         true
       end
     {% end %}
diff --git a/src/ameba/ast/flow_expression.cr b/src/ameba/ast/flow_expression.cr
index e20edc94..174111f2 100644
--- a/src/ameba/ast/flow_expression.cr
+++ b/src/ameba/ast/flow_expression.cr
@@ -58,7 +58,9 @@ module Ameba::AST
           control_flow_found ||= !loop?(exp) && flow_expression?(exp, in_loop?)
         end
       when Crystal::BinaryOp
-        unreachable_nodes << current_node.right if flow_expression?(current_node.left, in_loop?)
+        if flow_expression?(current_node.left, in_loop?)
+          unreachable_nodes << current_node.right
+        end
       end
 
       unreachable_nodes
diff --git a/src/ameba/ast/scope.cr b/src/ameba/ast/scope.cr
index bcae082c..4a114930 100644
--- a/src/ameba/ast/scope.cr
+++ b/src/ameba/ast/scope.cr
@@ -106,6 +106,7 @@ module Ameba::AST
     # ```
     def spawn_block?
       return false unless node.is_a?(Crystal::Block)
+
       call = node.as(Crystal::Block).call
       call.try(&.name) == "spawn"
     end
diff --git a/src/ameba/ast/util.cr b/src/ameba/ast/util.cr
index 3b210661..07eff507 100644
--- a/src/ameba/ast/util.cr
+++ b/src/ameba/ast/util.cr
@@ -32,7 +32,6 @@ module Ameba::AST::Util
   # to determine and cut a piece of source of the node.
   def node_source(node, code_lines)
     loc, end_loc = node.location, node.end_location
-
     return unless loc && end_loc
 
     source_between(loc, end_loc, code_lines)
@@ -46,7 +45,7 @@ module Ameba::AST::Util
     first_line, last_line = node_lines[0]?, node_lines[-1]?
 
     return if first_line.nil? || last_line.nil?
-    return if first_line.size < column # compiler reports incorrection location
+    return if first_line.size < column # compiler reports incorrect location
 
     node_lines[0] = first_line.sub(0...column, "")
 
@@ -162,11 +161,11 @@ module Ameba::AST::Util
   # Returns the exp code of a control expression.
   # Wraps implicit tuple literal with curly brackets (e.g. multi-return).
   def control_exp_code(node : Crystal::ControlExpression, code_lines)
-    return unless (exp = node.exp)
-    return unless (exp_code = node_source(exp, code_lines))
+    return unless exp = node.exp
+    return unless exp_code = node_source(exp, code_lines)
     return exp_code unless exp.is_a?(Crystal::TupleLiteral) && exp_code[0] != '{'
-    return unless (exp_start = exp.elements.first.location)
-    return unless (exp_end = exp.end_location)
+    return unless exp_start = exp.elements.first.location
+    return unless exp_end = exp.end_location
 
     "{#{source_between(exp_start, exp_end, code_lines)}}"
   end
diff --git a/src/ameba/ast/variabling/argument.cr b/src/ameba/ast/variabling/argument.cr
index 91204f0e..7683eccb 100644
--- a/src/ameba/ast/variabling/argument.cr
+++ b/src/ameba/ast/variabling/argument.cr
@@ -39,10 +39,10 @@ module Ameba::AST
     # Name of the argument.
     def name
       case current_node = node
-      when Crystal::Var then current_node.name
-      when Crystal::Arg then current_node.name
+      when Crystal::Var, Crystal::Arg
+        current_node.name
       else
-        raise ArgumentError.new "invalid node"
+        raise ArgumentError.new "Invalid node"
       end
     end
   end
diff --git a/src/ameba/ast/variabling/assignment.cr b/src/ameba/ast/variabling/assignment.cr
index bc83c378..11a7fbbc 100644
--- a/src/ameba/ast/variabling/assignment.cr
+++ b/src/ameba/ast/variabling/assignment.cr
@@ -97,6 +97,7 @@ module Ameba::AST
       return false unless (assign = node).is_a?(Crystal::Assign)
       return false unless (value = assign.value).is_a?(Crystal::Call)
       return false unless (obj = value.obj).is_a?(Crystal::Var)
+
       obj.name.starts_with? "__arg"
     end
   end
diff --git a/src/ameba/ast/variabling/variable.cr b/src/ameba/ast/variabling/variable.cr
index 088f81e1..19bad442 100644
--- a/src/ameba/ast/variabling/variable.cr
+++ b/src/ameba/ast/variabling/variable.cr
@@ -1,8 +1,8 @@
 module Ameba::AST
   # Represents the existence of the local variable.
-  # Holds the var node and variable assigments.
+  # Holds the var node and variable assignments.
   class Variable
-    # List of the assigments of this variable.
+    # List of the assignments of this variable.
     getter assignments = [] of Assignment
 
     # List of the references of this variable.
@@ -30,7 +30,7 @@ module Ameba::AST
     def initialize(@node, @scope)
     end
 
-    # Returns true if it is a special variable, i.e `$?`.
+    # Returns `true` if it is a special variable, i.e `$?`.
     def special?
       @node.special_var?
     end
@@ -50,7 +50,7 @@ module Ameba::AST
       update_assign_reference!
     end
 
-    # Returns true if variable has any reference.
+    # Returns `true` if variable has any reference.
     #
     # ```
     # variable = Variable.new(node, scope)
@@ -85,7 +85,7 @@ module Ameba::AST
       consumed_branches = Set(Branch).new
 
       assignments.reverse_each do |assignment|
-        next if consumed_branches.includes?(assignment.branch)
+        next if assignment.branch.in?(consumed_branches)
         assignment.referenced = true
 
         break unless branch = assignment.branch
@@ -93,7 +93,7 @@ module Ameba::AST
       end
     end
 
-    # Returns true if the current var is referenced in
+    # Returns `true` if the current var is referenced in
     # in the block. For example this variable is captured
     # by block:
     #
@@ -110,26 +110,29 @@ module Ameba::AST
     # ```
     def captured_by_block?(scope = @scope)
       scope.inner_scopes.each do |inner_scope|
-        return true if inner_scope.block? && inner_scope.references?(self, check_inner_scopes: false)
+        return true if inner_scope.block? &&
+                       inner_scope.references?(self, check_inner_scopes: false)
         return true if captured_by_block?(inner_scope)
       end
 
       false
     end
 
-    # Returns true if current variable potentially referenced in a macro,
-    # false if not.
+    # Returns `true` if current variable potentially referenced in a macro,
+    # `false` if not.
     def used_in_macro?(scope = @scope)
       scope.inner_scopes.each do |inner_scope|
         return true if MacroReferenceFinder.new(inner_scope.node, node.name).references
       end
       return true if MacroReferenceFinder.new(scope.node, node.name).references
-      return true if (outer_scope = scope.outer_scope) && used_in_macro?(outer_scope)
+      return true if (outer_scope = scope.outer_scope) &&
+                     used_in_macro?(outer_scope)
+
       false
     end
 
-    # Returns true if the variable is a target (on the left) of the assignment,
-    # false otherwise.
+    # Returns `true` if the variable is a target (on the left) of the assignment,
+    # `false` otherwise.
     def target_of?(assign)
       case assign
       when Crystal::Assign           then eql?(assign.target)
@@ -141,12 +144,12 @@ module Ameba::AST
       end
     end
 
-    # Returns true if the name starts with '_', false if not.
+    # Returns `true` if the name starts with '_', `false` if not.
     def ignored?
       name.starts_with? '_'
     end
 
-    # Returns true if the `node` represents exactly
+    # Returns `true` if the `node` represents exactly
     # the same Crystal node as `@node`.
     def eql?(node)
       node.is_a?(Crystal::Var) &&
@@ -154,7 +157,7 @@ module Ameba::AST
         node.location == @node.location
     end
 
-    # Returns true if the variable is declared before the `node`.
+    # Returns `true` if the variable is declared before the `node`.
     def declared_before?(node)
       var_location, node_location = location, node.location
 
diff --git a/src/ameba/ast/visitors/counting_visitor.cr b/src/ameba/ast/visitors/counting_visitor.cr
index 896baa64..a9e7dc72 100644
--- a/src/ameba/ast/visitors/counting_visitor.cr
+++ b/src/ameba/ast/visitors/counting_visitor.cr
@@ -2,6 +2,7 @@ module Ameba::AST
   # AST Visitor that counts occurrences of certain keywords
   class CountingVisitor < Crystal::Visitor
     DEFAULT_COMPLEXITY = 1
+
     getter macro_condition = false
 
     # Creates a new counting visitor
@@ -44,6 +45,7 @@ module Ameba::AST
     def visit(node : Crystal::MacroIf | Crystal::MacroFor)
       @macro_condition = true
       @complexity = DEFAULT_COMPLEXITY
+
       false
     end
   end
diff --git a/src/ameba/ast/visitors/node_visitor.cr b/src/ameba/ast/visitors/node_visitor.cr
index a37eea08..2c35adb1 100644
--- a/src/ameba/ast/visitors/node_visitor.cr
+++ b/src/ameba/ast/visitors/node_visitor.cr
@@ -45,11 +45,11 @@ module Ameba::AST
     end
 
     {% for name in NODES %}
-      # A visit callback for `Crystal::{{name}}` node.
+      # A visit callback for `Crystal::{{ name }}` node.
       #
       # Returns `true` if the child nodes should be traversed as well,
       # `false` otherwise.
-      def visit(node : Crystal::{{name}})
+      def visit(node : Crystal::{{ name }})
         return false if skip?(node)
 
         @rule.test @source, node
diff --git a/src/ameba/ast/visitors/scope_visitor.cr b/src/ameba/ast/visitors/scope_visitor.cr
index 06931ff3..5abf4056 100644
--- a/src/ameba/ast/visitors/scope_visitor.cr
+++ b/src/ameba/ast/visitors/scope_visitor.cr
@@ -48,7 +48,8 @@ module Ameba::AST
     end
 
     private def on_assign_end(target, node)
-      target.is_a?(Crystal::Var) && @current_scope.assign_variable(target.name, node)
+      target.is_a?(Crystal::Var) &&
+        @current_scope.assign_variable(target.name, node)
     end
 
     # :nodoc:
@@ -58,7 +59,7 @@ module Ameba::AST
 
     {% for name in NODES %}
       # :nodoc:
-      def visit(node : Crystal::{{name}})
+      def visit(node : Crystal::{{ name }})
         on_scope_enter(node)
       end
     {% end %}
@@ -96,13 +97,15 @@ module Ameba::AST
 
     # :nodoc:
     def visit(node : Crystal::TypeDeclaration)
-      return if @current_scope.type_definition? || !(var = node.var).is_a?(Crystal::Var)
-      @current_scope.add_variable var
+      return if @current_scope.type_definition?
+      return if !(var = node.var).is_a?(Crystal::Var)
+
+      @current_scope.add_variable(var)
     end
 
     # :nodoc:
     def visit(node : Crystal::Arg)
-      @current_scope.add_argument node
+      @current_scope.add_argument(node)
     end
 
     # :nodoc:
@@ -114,11 +117,12 @@ module Ameba::AST
     def visit(node : Crystal::Var)
       variable = @current_scope.find_variable node.name
 
-      if @current_scope.arg?(node) # node is an argument
+      case
+      when @current_scope.arg?(node) # node is an argument
         @current_scope.add_argument(node)
-      elsif variable.nil? && @current_assign # node is a variable
+      when variable.nil? && @current_assign # node is a variable
         @current_scope.add_variable(node)
-      elsif variable # node is a reference
+      when variable # node is a reference
         reference = variable.reference node, @current_scope
         if @current_assign.is_a?(Crystal::OpAssign) || !reference.target_of?(@current_assign)
           variable.reference_assignments!
diff --git a/src/ameba/config.cr b/src/ameba/config.cr
index 23f37fe7..8f5b52a4 100644
--- a/src/ameba/config.cr
+++ b/src/ameba/config.cr
@@ -123,10 +123,10 @@ class Ameba::Config
   # config.formatter = :progress
   # ```
   def formatter=(name : String | Symbol)
-    unless f = AVAILABLE_FORMATTERS[name]?
+    unless formatter = AVAILABLE_FORMATTERS[name]?
       raise "Unknown formatter `#{name}`. Use one of #{Config.formatter_names}."
     end
-    @formatter = f.new
+    @formatter = formatter.new
   end
 
   # Updates rule properties.
@@ -180,7 +180,7 @@ class Ameba::Config
     when .as_s? then [value.to_s]
     when .as_a? then value.as_a.map(&.as_s)
     else
-      raise "incorrect '#{section_name}' section in a config files"
+      raise "Incorrect '#{section_name}' section in a config files"
     end
   end
 
@@ -241,8 +241,8 @@ class Ameba::Config
 
         {% properties[name] = {key: key, default: value, type: type, converter: converter} %}
 
-        @[YAML::Field(key: {{key}}, converter: {{converter}}, type: {{type}})]
-        property {{name}} : {{type}} = {{value}}
+        @[YAML::Field(key: {{ key }}, converter: {{ converter }}, type: {{ type }})]
+        property {{ name }} : {{ type }} = {{ value }}
       {% end %}
 
       {% if properties["enabled".id] == nil %}
@@ -253,7 +253,7 @@ class Ameba::Config
       {% if properties["severity".id] == nil %}
         {% default = @type.name.starts_with?("Ameba::Rule::Lint") ? "Ameba::Severity::Warning".id : "Ameba::Severity::Convention".id %}
         @[YAML::Field(key: "Severity", converter: Ameba::SeverityYamlConverter)]
-        property severity = {{default}}
+        property severity = {{ default }}
       {% end %}
 
       {% if properties["excluded".id] == nil %}
diff --git a/src/ameba/formatter/explain_formatter.cr b/src/ameba/formatter/explain_formatter.cr
index 33c8b7d5..ebd985a1 100644
--- a/src/ameba/formatter/explain_formatter.cr
+++ b/src/ameba/formatter/explain_formatter.cr
@@ -38,7 +38,7 @@ module Ameba::Formatter
     private def explain(source, issue)
       rule = issue.rule
 
-      return unless (location = issue.location)
+      return unless location = issue.location
 
       output_title "ISSUE INFO"
       output_paragraph [
diff --git a/src/ameba/formatter/util.cr b/src/ameba/formatter/util.cr
index cbf0907c..fb3f226e 100644
--- a/src/ameba/formatter/util.cr
+++ b/src/ameba/formatter/util.cr
@@ -41,7 +41,7 @@ module Ameba::Formatter
     end
 
     def affected_code(issue : Issue, context_lines = 0, max_length = 120, ellipsis = " ...", prompt = "> ")
-      return unless (location = issue.location)
+      return unless location = issue.location
 
       affected_code(issue.code, location, issue.end_location, context_lines, max_length, ellipsis, prompt)
     end
diff --git a/src/ameba/inline_comments.cr b/src/ameba/inline_comments.cr
index 446e9eab..d5724bee 100644
--- a/src/ameba/inline_comments.cr
+++ b/src/ameba/inline_comments.cr
@@ -1,7 +1,8 @@
 module Ameba
   # A module that utilizes inline comments parsing and processing logic.
   module InlineComments
-    COMMENT_DIRECTIVE_REGEX = /# ameba:(?<action>\w+) (?<rules>\w+(?:\/\w+)?(?:,? \w+(?:\/\w+)?)*)/
+    COMMENT_DIRECTIVE_REGEX =
+      /# ameba:(?<action>\w+) (?<rules>\w+(?:\/\w+)?(?:,? \w+(?:\/\w+)?)*)/
 
     # Available actions in the inline comments
     enum Action
@@ -87,15 +88,17 @@ module Ameba
       return false unless directive = parse_inline_directive(line)
       return false unless Action.parse?(directive[:action]).try(&.disable?)
 
-      directive[:rules].includes?(rule.name) ||
-        directive[:rules].includes?(rule.group)
+      rules = directive[:rules]
+      rules.includes?(rule.name) || rules.includes?(rule.group)
     end
 
     private def commented_out?(line)
       commented = false
 
       lexer = Crystal::Lexer.new(line).tap(&.comments_enabled = true)
-      Tokenizer.new(lexer).run { |t| commented = true if t.type.comment? }
+      Tokenizer.new(lexer).run do |token|
+        commented = true if token.type.comment?
+      end
       commented
     end
   end
diff --git a/src/ameba/rule/base.cr b/src/ameba/rule/base.cr
index 70ae53d8..e261a10b 100644
--- a/src/ameba/rule/base.cr
+++ b/src/ameba/rule/base.cr
@@ -33,7 +33,7 @@ module Ameba::Rule
     # that are tested by this rule, it should add an issue.
     #
     # Be default it uses a node visitor to traverse all the nodes in the source.
-    # Must be overriten for other type of rules.
+    # NOTE: Must be overridden for other type of rules.
     def test(source : Source)
       AST::NodeVisitor.new self, source
     end
@@ -64,7 +64,7 @@ module Ameba::Rule
     # MyRule.new.name # => "MyRule"
     # ```
     def name
-      {{@type}}.rule_name
+      {{ @type }}.rule_name
     end
 
     # Returns a group this rule belong to.
@@ -77,7 +77,7 @@ module Ameba::Rule
     # MyGroup::MyRule.new.group # => "MyGroup"
     # ```
     def group
-      {{@type}}.group_name
+      {{ @type }}.group_name
     end
 
     # Checks whether the source is excluded from this rule.
@@ -113,7 +113,7 @@ module Ameba::Rule
     end
 
     macro issue_for(*args, **kwargs, &block)
-      source.add_issue(self, {{*args}}, {{**kwargs}}) {{block}}
+      source.add_issue(self, {{ *args }}, {{ **kwargs }}) {{ block }}
     end
 
     protected def self.rule_name
diff --git a/src/ameba/rule/layout/trailing_whitespace.cr b/src/ameba/rule/layout/trailing_whitespace.cr
index b579e096..471f3795 100644
--- a/src/ameba/rule/layout/trailing_whitespace.cr
+++ b/src/ameba/rule/layout/trailing_whitespace.cr
@@ -1,5 +1,5 @@
 module Ameba::Rule::Layout
-  # A rule that disallows trailing whitespaces.
+  # A rule that disallows trailing whitespace.
   #
   # YAML configuration example:
   #
diff --git a/src/ameba/rule/lint/duplicated_require.cr b/src/ameba/rule/lint/duplicated_require.cr
index 0e33dbb0..d1fe1295 100644
--- a/src/ameba/rule/lint/duplicated_require.cr
+++ b/src/ameba/rule/lint/duplicated_require.cr
@@ -23,7 +23,7 @@ module Ameba::Rule::Lint
     def test(source)
       nodes = AST::TopLevelNodesVisitor.new(source.ast).require_nodes
       nodes.each_with_object([] of String) do |node, processed_require_strings|
-        issue_for(node, MSG % node.string) if processed_require_strings.includes?(node.string)
+        issue_for(node, MSG % node.string) if node.string.in?(processed_require_strings)
         processed_require_strings << node.string
       end
     end
diff --git a/src/ameba/rule/lint/not_nil_after_no_bang.cr b/src/ameba/rule/lint/not_nil_after_no_bang.cr
index d222c43e..e0dab6e0 100644
--- a/src/ameba/rule/lint/not_nil_after_no_bang.cr
+++ b/src/ameba/rule/lint/not_nil_after_no_bang.cr
@@ -54,7 +54,7 @@ module Ameba::Rule::Lint
 
       issue_for name_location, end_location, msg do |corrector|
         corrector.insert_after(name_location_end, '!')
-        corrector.remove_trailing(node, ".not_nil!".size)
+        corrector.remove_trailing(node, {{ ".not_nil!".size }})
       end
     end
   end
diff --git a/src/ameba/rule/style/guard_clause.cr b/src/ameba/rule/style/guard_clause.cr
index 90800ad6..4689f6e9 100644
--- a/src/ameba/rule/style/guard_clause.cr
+++ b/src/ameba/rule/style/guard_clause.cr
@@ -75,8 +75,8 @@ module Ameba::Rule::Style
         end
 
       case final_expression
-      when Crystal::If     then check_ending_if(source, final_expression)
-      when Crystal::Unless then check_ending_if(source, final_expression)
+      when Crystal::If, Crystal::Unless
+        check_ending_if(source, final_expression)
       end
     end
 
@@ -92,7 +92,8 @@ module Ameba::Rule::Style
 
       return unless guard_clause && parent && conditional_keyword
 
-      report_issue(source, node, guard_clause_source(source, guard_clause, parent), conditional_keyword)
+      guard_clause_source = guard_clause_source(source, guard_clause, parent)
+      report_issue(source, node, guard_clause_source, conditional_keyword)
     end
 
     private def check_ending_if(source, node)
@@ -113,10 +114,11 @@ module Ameba::Rule::Style
       if node.else.is_a?(Crystal::Nop)
         return unless end_end_loc = node.end_location
 
-        end_loc = end_end_loc.adjust(column_number: {{1 - "end".size}})
+        end_loc = end_end_loc.adjust(column_number: {{ 1 - "end".size }})
 
         issue_for keyword_loc, keyword_end_loc, MSG % example do |corrector|
-          corrector.replace(keyword_loc, keyword_end_loc, "#{scope_exiting_keyword} #{conditional_keyword}")
+          replacement = "#{scope_exiting_keyword} #{conditional_keyword}"
+          corrector.replace(keyword_loc, keyword_end_loc, replacement)
           corrector.remove(end_loc, end_end_loc)
         end
       else
diff --git a/src/ameba/rule/style/is_a_filter.cr b/src/ameba/rule/style/is_a_filter.cr
index 4ebb116e..6337040d 100644
--- a/src/ameba/rule/style/is_a_filter.cr
+++ b/src/ameba/rule/style/is_a_filter.cr
@@ -59,8 +59,8 @@ module Ameba::Rule::Style
 
     def test(source, node : Crystal::Call)
       return unless node.name.in?(filter_names)
-      return unless (filter_location = node.name_location)
-      return unless (block = node.block)
+      return unless filter_location = node.name_location
+      return unless block = node.block
       return unless (body = block.body).is_a?(Crystal::IsA)
       return unless (path = body.const).is_a?(Crystal::Path)
       return unless body.obj.is_a?(Crystal::Var)
diff --git a/src/ameba/rule/style/redundant_next.cr b/src/ameba/rule/style/redundant_next.cr
index 8f9acb5c..b0e8b1eb 100644
--- a/src/ameba/rule/style/redundant_next.cr
+++ b/src/ameba/rule/style/redundant_next.cr
@@ -116,7 +116,7 @@ module Ameba::Rule::Style
       return if allow_multi_next && node.exp.is_a?(Crystal::TupleLiteral)
       return if allow_empty_next && (node.exp.nil? || node.exp.try(&.nop?))
 
-      if (exp_code = control_exp_code(node, source.lines))
+      if exp_code = control_exp_code(node, source.lines)
         issue_for node, MSG do |corrector|
           corrector.replace(node, exp_code)
         end
diff --git a/src/ameba/rule/style/redundant_return.cr b/src/ameba/rule/style/redundant_return.cr
index a85ea7ef..329fab76 100644
--- a/src/ameba/rule/style/redundant_return.cr
+++ b/src/ameba/rule/style/redundant_return.cr
@@ -113,7 +113,7 @@ module Ameba::Rule::Style
       return if allow_multi_return && node.exp.is_a?(Crystal::TupleLiteral)
       return if allow_empty_return && (node.exp.nil? || node.exp.try(&.nop?))
 
-      if (exp_code = control_exp_code(node, source.lines))
+      if exp_code = control_exp_code(node, source.lines)
         issue_for node, MSG do |corrector|
           corrector.replace(node, exp_code)
         end
diff --git a/src/ameba/rule/style/variable_names.cr b/src/ameba/rule/style/variable_names.cr
index 2176dbec..44615ab3 100644
--- a/src/ameba/rule/style/variable_names.cr
+++ b/src/ameba/rule/style/variable_names.cr
@@ -55,11 +55,11 @@ module Ameba::Rule::Style
       private getter var_locations = [] of Crystal::Location
 
       def visit(node : Crystal::Var)
-        !var_locations.includes?(node.location) && super
+        !node.location.in?(var_locations) && super
       end
 
       def visit(node : Crystal::InstanceVar | Crystal::ClassVar)
-        if (location = node.location)
+        if location = node.location
           var_locations << location
         end
         super
diff --git a/src/ameba/rule/style/while_true.cr b/src/ameba/rule/style/while_true.cr
index be83d62b..189a8c11 100644
--- a/src/ameba/rule/style/while_true.cr
+++ b/src/ameba/rule/style/while_true.cr
@@ -34,8 +34,8 @@ module Ameba::Rule::Style
 
     def test(source, node : Crystal::While)
       return unless node.cond.true_literal?
-      return unless (location = node.location)
-      return unless (end_location = node.cond.end_location)
+      return unless location = node.location
+      return unless end_location = node.cond.end_location
 
       issue_for node, MSG do |corrector|
         corrector.replace(location, end_location, "loop do")
diff --git a/src/ameba/runner.cr b/src/ameba/runner.cr
index ffe56d48..fb709464 100644
--- a/src/ameba/runner.cr
+++ b/src/ameba/runner.cr
@@ -87,6 +87,7 @@ module Ameba
     # ```
     def run
       @formatter.started @sources
+
       channels = @sources.map { Channel(Exception?).new }
       @sources.each_with_index do |source, idx|
         channel = channels[idx]
@@ -219,7 +220,9 @@ module Ameba
     end
 
     private def check_unneeded_directives(source)
-      return unless (rule = @unneeded_disable_directive_rule) && rule.enabled
+      return unless rule = @unneeded_disable_directive_rule
+      return unless rule.enabled
+
       rule.test(source)
     end
   end
diff --git a/src/ameba/source.cr b/src/ameba/source.cr
index d6e0b97d..787874d3 100644
--- a/src/ameba/source.cr
+++ b/src/ameba/source.cr
@@ -36,7 +36,7 @@ module Ameba
       true
     end
 
-    # Returns lines of code splitted by new line character.
+    # Returns lines of code split by new line character.
     # Since `code` is immutable and can't be changed, this
     # method caches lines in an instance variable, so calling
     # it second time will not perform a split, but will return
diff --git a/src/ameba/source/rewriter/action.cr b/src/ameba/source/rewriter/action.cr
index 23a009ec..e2df77d2 100644
--- a/src/ameba/source/rewriter/action.cr
+++ b/src/ameba/source/rewriter/action.cr
@@ -32,10 +32,12 @@ class Ameba::Source::Rewriter
 
     def empty?
       replacement = @replacement
+
       @insert_before.empty? &&
         @insert_after.empty? &&
         @children.empty? &&
-        (replacement.nil? || (replacement.empty? && @begin_pos == @end_pos))
+        (replacement.nil? ||
+          (replacement.empty? && @begin_pos == @end_pos))
     end
 
     def ordered_replacements
@@ -50,7 +52,10 @@ class Ameba::Source::Rewriter
 
     def insertion?
       replacement = @replacement
-      !@insert_before.empty? || !@insert_after.empty? || (replacement && !replacement.empty?)
+
+      !@insert_before.empty? ||
+        !@insert_after.empty? ||
+        (replacement && !replacement.empty?)
     end
 
     protected def with(*,
diff --git a/src/ameba/spec/annotated_source.cr b/src/ameba/spec/annotated_source.cr
index 7a33d3df..d121d560 100644
--- a/src/ameba/spec/annotated_source.cr
+++ b/src/ameba/spec/annotated_source.cr
@@ -17,12 +17,13 @@ class Ameba::Spec::AnnotatedSource
     annotations = [] of {Int32, String, String}
     code_lines = annotated_code.split('\n') # must preserve trailing newline
     code_lines.each do |code_line|
-      if (annotation_match = ANNOTATION_PATTERN_1.match(code_line))
+      case
+      when annotation_match = ANNOTATION_PATTERN_1.match(code_line)
         message_index = annotation_match.end
         prefix = code_line[0...message_index]
         message = code_line[message_index...]
         annotations << {lines.size, prefix, message}
-      elsif (annotation_index = code_line.index(ANNOTATION_PATTERN_2))
+      when annotation_index = code_line.index(ANNOTATION_PATTERN_2)
         lines << code_line[...annotation_index]
         message_index = annotation_index + ANNOTATION_PATTERN_2.size
         message = code_line[message_index...]