diff --git a/src/ameba/ast/variabling/assignment.cr b/src/ameba/ast/variabling/assignment.cr
index 6908572a..626e847f 100644
--- a/src/ameba/ast/variabling/assignment.cr
+++ b/src/ameba/ast/variabling/assignment.cr
@@ -49,7 +49,7 @@ module Ameba::AST
     # a ||= 1
     # ```
     def op_assign?
-      node.is_a? Crystal::OpAssign
+      node.is_a?(Crystal::OpAssign)
     end
 
     # Returns true if this assignment is in a branch, false if not.
diff --git a/src/ameba/ast/variabling/variable.cr b/src/ameba/ast/variabling/variable.cr
index 1a7eab42..526b417f 100644
--- a/src/ameba/ast/variabling/variable.cr
+++ b/src/ameba/ast/variabling/variable.cr
@@ -91,8 +91,8 @@ module Ameba::AST
         next if consumed_branches.includes?(assignment.branch)
         assignment.referenced = true
 
-        break unless assignment.branch
-        consumed_branches << assignment.branch.not_nil!
+        break unless branch = assignment.branch
+        consumed_branches << branch
       end
     end
 
diff --git a/src/ameba/config.cr b/src/ameba/config.cr
index 5bf0261e..c3f7b339 100644
--- a/src/ameba/config.cr
+++ b/src/ameba/config.cr
@@ -270,7 +270,7 @@ class Ameba::Config
         include YAML::Serializable::Strict
 
         def self.new(config = nil)
-          if (raw = config.try &.raw).is_a? Hash
+          if (raw = config.try &.raw).is_a?(Hash)
             yaml = raw[rule_name]?.try &.to_yaml
           end
           from_yaml yaml || "{}"
diff --git a/src/ameba/formatter/todo_formatter.cr b/src/ameba/formatter/todo_formatter.cr
index 88584d1d..47314407 100644
--- a/src/ameba/formatter/todo_formatter.cr
+++ b/src/ameba/formatter/todo_formatter.cr
@@ -41,7 +41,7 @@ module Ameba::Formatter
     private def rule_issues_map(issues)
       Hash(Rule::Base, Array(Issue)).new.tap do |h|
         issues.each do |issue|
-          next if issue.disabled? || issue.rule.is_a? Rule::Lint::Syntax
+          next if issue.disabled? || issue.rule.is_a?(Rule::Lint::Syntax)
           (h[issue.rule] ||= Array(Issue).new) << issue
         end
       end
diff --git a/src/ameba/rule/lint/literal_in_condition.cr b/src/ameba/rule/lint/literal_in_condition.cr
index 15478516..642350d6 100644
--- a/src/ameba/rule/lint/literal_in_condition.cr
+++ b/src/ameba/rule/lint/literal_in_condition.cr
@@ -30,8 +30,7 @@ module Ameba::Rule::Lint
     MSG = "Literal value found in conditional"
 
     def check_node(source, node)
-      return unless literal?(node.cond)
-      issue_for node, MSG
+      issue_for node, MSG if literal?(node.cond)
     end
 
     def test(source, node : Crystal::If)
diff --git a/src/ameba/rule/lint/percent_array.cr b/src/ameba/rule/lint/percent_array.cr
index b8bb1b54..c8ea02a3 100644
--- a/src/ameba/rule/lint/percent_array.cr
+++ b/src/ameba/rule/lint/percent_array.cr
@@ -26,8 +26,8 @@ module Ameba::Rule::Lint
   struct PercentArrays < Base
     properties do
       description "Disallows some unwanted symbols in percent array literals"
-      string_array_unwanted_symbols ",\""
-      symbol_array_unwanted_symbols ",:"
+      string_array_unwanted_symbols %(,")
+      symbol_array_unwanted_symbols %(,:)
     end
 
     MSG = "Symbols `%s` may be unwanted in %s array literals"
@@ -62,8 +62,7 @@ module Ameba::Rule::Lint
     end
 
     private def check_array_entry(entry, symbols, literal)
-      return unless entry =~ /[#{symbols}]/
-      MSG % {symbols, literal}
+      MSG % {symbols, literal} if entry =~ /[#{symbols}]/
     end
   end
 end
diff --git a/src/ameba/rule/lint/rand_zero.cr b/src/ameba/rule/lint/rand_zero.cr
index efd8ab7b..ad1843ca 100644
--- a/src/ameba/rule/lint/rand_zero.cr
+++ b/src/ameba/rule/lint/rand_zero.cr
@@ -33,7 +33,7 @@ module Ameba::Rule::Lint
       return unless node.name == "rand" &&
                     node.args.size == 1 &&
                     (arg = node.args.first) &&
-                    (arg.is_a? Crystal::NumberLiteral) &&
+                    arg.is_a?(Crystal::NumberLiteral) &&
                     (value = arg.value) &&
                     value.in?("0", "1")
 
diff --git a/src/ameba/rule/lint/redundant_string_coercion.cr b/src/ameba/rule/lint/redundant_string_coercion.cr
index 4e85de49..f451e9ea 100644
--- a/src/ameba/rule/lint/redundant_string_coercion.cr
+++ b/src/ameba/rule/lint/redundant_string_coercion.cr
@@ -30,7 +30,9 @@ module Ameba::Rule::Lint
     MSG = "Redundant use of `Object#to_s` in interpolation"
 
     def test(source, node : Crystal::StringInterpolation)
-      string_coercion_nodes(node).each { |n| issue_for n.name_location, n.end_location, MSG }
+      string_coercion_nodes(node).each do |n|
+        issue_for n.name_location, n.end_location, MSG
+      end
     end
 
     private def string_coercion_nodes(node)
diff --git a/src/ameba/rule/lint/shadowed_exception.cr b/src/ameba/rule/lint/shadowed_exception.cr
index a937f8bb..84f2f435 100644
--- a/src/ameba/rule/lint/shadowed_exception.cr
+++ b/src/ameba/rule/lint/shadowed_exception.cr
@@ -41,11 +41,10 @@ module Ameba::Rule::Lint
     MSG = "Exception handler has shadowed exceptions: %s"
 
     def test(source, node : Crystal::ExceptionHandler)
-      return unless excs = node.rescues
+      return unless excs = node.rescues.try &.map(&.types)
+      return if (excs = shadowed excs).empty?
 
-      if (excs = shadowed excs.map(&.types)).any?
-        issue_for node, MSG % excs.join(", ")
-      end
+      issue_for node, MSG % excs.join(", ")
     end
 
     private def shadowed(exceptions, exception_found = false)
diff --git a/src/ameba/rule/metrics/cyclomatic_complexity.cr b/src/ameba/rule/metrics/cyclomatic_complexity.cr
index 167ebfe7..9ce2bce4 100644
--- a/src/ameba/rule/metrics/cyclomatic_complexity.cr
+++ b/src/ameba/rule/metrics/cyclomatic_complexity.cr
@@ -20,9 +20,8 @@ module Ameba::Rule::Metrics
       complexity = AST::CountingVisitor.new(node).count
 
       if complexity > max_complexity && (location = node.name_location)
-        issue_for location, def_name_end_location(node), MSG % {
-          complexity, max_complexity,
-        }
+        issue_for location, def_name_end_location(node),
+          MSG % {complexity, max_complexity}
       end
     end
 
diff --git a/src/ameba/rule/performance/any_after_filter.cr b/src/ameba/rule/performance/any_after_filter.cr
index b8aa3f34..c6dbc2b7 100644
--- a/src/ameba/rule/performance/any_after_filter.cr
+++ b/src/ameba/rule/performance/any_after_filter.cr
@@ -35,12 +35,10 @@ module Ameba::Rule::Performance
 
     def test(source, node : Crystal::Call)
       return unless node.name == ANY_NAME && (obj = node.obj)
-      return unless obj.is_a?(Crystal::Call)
-      return if obj.block.nil? || !node.block.nil?
+      return unless obj.is_a?(Crystal::Call) && obj.block && node.block.nil?
+      return unless filter_names.includes?(obj.name)
 
-      if filter_names.includes?(obj.name)
-        issue_for obj.name_location, node.name_end_location, MSG % obj.name
-      end
+      issue_for obj.name_location, node.name_end_location, MSG % obj.name
     end
   end
 end
diff --git a/src/ameba/rule/performance/first_last_after_filter.cr b/src/ameba/rule/performance/first_last_after_filter.cr
index 78f3302a..ced0a1e3 100644
--- a/src/ameba/rule/performance/first_last_after_filter.cr
+++ b/src/ameba/rule/performance/first_last_after_filter.cr
@@ -44,13 +44,12 @@ module Ameba::Rule::Performance
 
     def test(source, node : Crystal::Call)
       return unless CALL_NAMES.includes?(node.name) && (obj = node.obj)
-      return unless obj.is_a?(Crystal::Call)
-      return if obj.block.nil? || !node.block.nil? || node.args.any?
+      return unless obj.is_a?(Crystal::Call) && obj.block
+      return if !node.block.nil? || node.args.any?
+      return unless filter_names.includes?(obj.name)
 
-      if filter_names.includes?(obj.name)
-        message = node.name.includes?(CALL_NAMES.first) ? MSG : MSG_REVERSE
-        issue_for obj.name_location, node.name_end_location, message % {obj.name, node.name}
-      end
+      message = node.name.includes?(CALL_NAMES.first) ? MSG : MSG_REVERSE
+      issue_for obj.name_location, node.name_end_location, message % {obj.name, node.name}
     end
   end
 end
diff --git a/src/ameba/rule/performance/size_after_filter.cr b/src/ameba/rule/performance/size_after_filter.cr
index 6a281432..0339f998 100644
--- a/src/ameba/rule/performance/size_after_filter.cr
+++ b/src/ameba/rule/performance/size_after_filter.cr
@@ -50,12 +50,10 @@ module Ameba::Rule::Performance
 
     def test(source, node : Crystal::Call)
       return unless node.name == SIZE_NAME && (obj = node.obj)
-      return unless obj.is_a?(Crystal::Call)
-      return if obj.block.nil?
+      return unless obj.is_a?(Crystal::Call) && obj.block
+      return unless filter_names.includes?(obj.name)
 
-      if filter_names.includes?(obj.name)
-        issue_for obj.name_location, node.name_end_location, MSG % obj.name
-      end
+      issue_for obj.name_location, node.name_end_location, MSG % obj.name
     end
   end
 end
diff --git a/src/ameba/rule/style/constant_names.cr b/src/ameba/rule/style/constant_names.cr
index fdd7caad..180ed8be 100644
--- a/src/ameba/rule/style/constant_names.cr
+++ b/src/ameba/rule/style/constant_names.cr
@@ -29,7 +29,7 @@ module Ameba::Rule::Style
     MSG = "Constant name should be screaming-cased: %s, not %s"
 
     def test(source, node : Crystal::Assign)
-      if (target = node.target).is_a? Crystal::Path
+      if (target = node.target).is_a?(Crystal::Path)
         name = target.names.first
         expected = name.upcase
 
diff --git a/src/ameba/rule/style/is_a_nil.cr b/src/ameba/rule/style/is_a_nil.cr
index cbf4aced..4848cd2f 100644
--- a/src/ameba/rule/style/is_a_nil.cr
+++ b/src/ameba/rule/style/is_a_nil.cr
@@ -4,7 +4,7 @@ module Ameba::Rule::Style
   # This is considered bad:
   #
   # ```
-  # var.is_a? Nil
+  # var.is_a?(Nil)
   # ```
   #
   # And needs to be written as:
@@ -31,7 +31,8 @@ module Ameba::Rule::Style
       return if node.nil_check?
 
       const = node.const
-      return unless const.is_a?(Crystal::Path) && const.names == PATH_NIL_NAMES
+      return unless const.is_a?(Crystal::Path)
+      return unless const.names == PATH_NIL_NAMES
 
       issue_for const, MSG
     end
diff --git a/src/ameba/rule/style/negated_conditions_in_unless.cr b/src/ameba/rule/style/negated_conditions_in_unless.cr
index 7225c5df..2780e228 100644
--- a/src/ameba/rule/style/negated_conditions_in_unless.cr
+++ b/src/ameba/rule/style/negated_conditions_in_unless.cr
@@ -42,7 +42,7 @@ module Ameba::Rule::Style
       when Crystal::BinaryOp
         negated_condition?(node.left) || negated_condition?(node.right)
       when Crystal::Expressions
-        node.expressions.any? { |e| negated_condition? e }
+        node.expressions.any? { |e| negated_condition?(e) }
       when Crystal::Not
         true
       else