diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index fd81d0c..9b55b7f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -13,8 +13,9 @@ before_script:
 
 spec:
   script:
-  - crystal tool format --check
   - crystal spec
+  - bin/ameba
+  - crystal tool format --check
 
 pages:
   stage: deploy
diff --git a/README.md b/README.md
index 32f7304..716d432 100644
--- a/README.md
+++ b/README.md
@@ -341,6 +341,7 @@ Contributing
 
 Please make sure to run `crystal tool format` before submitting.
 The CI build checks for properly formatted code.
+[Ameba](https://github.com/veelenga/ameba) is run to check for code style.
 
 Tests must be written for any new functionality.
 Macros that create types are not as easy to test,
diff --git a/shard.yml b/shard.yml
index c77f919..369ac5e 100644
--- a/shard.yml
+++ b/shard.yml
@@ -7,3 +7,8 @@ authors:
 crystal: 0.27.2
 
 license: MIT
+
+development_dependencies:
+  ameba:
+    github: veelenga/ameba
+    version: ~> 0.9
diff --git a/spec/dsl/nested_example_group_builder_spec.cr b/spec/dsl/nested_example_group_builder_spec.cr
index 9d15dcf..cf41fb6 100644
--- a/spec/dsl/nested_example_group_builder_spec.cr
+++ b/spec/dsl/nested_example_group_builder_spec.cr
@@ -154,7 +154,7 @@ describe Spectator::DSL::NestedExampleGroupBuilder do
     it "adds a hook" do
       hook_called = false
       builder = Spectator::DSL::NestedExampleGroupBuilder.new("foo")
-      builder.add_around_each_hook(->(proc : ->) {
+      builder.add_around_each_hook(->(_proc : ->) {
         hook_called = true
       })
       root = Spectator::DSL::RootExampleGroupBuilder.new.build(Spectator::Internals::SampleValues.empty)
diff --git a/spec/dsl/root_example_group_builder_spec.cr b/spec/dsl/root_example_group_builder_spec.cr
index 96a9a7a..b4aeb9d 100644
--- a/spec/dsl/root_example_group_builder_spec.cr
+++ b/spec/dsl/root_example_group_builder_spec.cr
@@ -143,7 +143,7 @@ describe Spectator::DSL::RootExampleGroupBuilder do
     it "adds a hook" do
       hook_called = false
       builder = Spectator::DSL::RootExampleGroupBuilder.new
-      builder.add_around_each_hook(->(proc : ->) {
+      builder.add_around_each_hook(->(_proc : ->) {
         hook_called = true
       })
       group = builder.build(Spectator::Internals::SampleValues.empty)
diff --git a/spec/example_iterator_spec.cr b/spec/example_iterator_spec.cr
index 8ec5594..882387d 100644
--- a/spec/example_iterator_spec.cr
+++ b/spec/example_iterator_spec.cr
@@ -93,7 +93,7 @@ describe Spectator::ExampleIterator do
             end
           else
             Spectator::NestedExampleGroup.new(i.to_s, group, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty).tap do |sub_group|
-              sub_group.children = Array(Spectator::ExampleComponent).new(5) do |j|
+              sub_group.children = Array(Spectator::ExampleComponent).new(5) do |_|
                 PassingExample.new(sub_group, Spectator::Internals::SampleValues.empty).tap do |example|
                   expected_examples << example
                 end
@@ -113,7 +113,7 @@ describe Spectator::ExampleIterator do
             PassingExample.new(group, Spectator::Internals::SampleValues.empty)
           else
             Spectator::NestedExampleGroup.new(i.to_s, group, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty).tap do |sub_group|
-              sub_group.children = Array(Spectator::ExampleComponent).new(5) do |j|
+              sub_group.children = Array(Spectator::ExampleComponent).new(5) do |_|
                 PassingExample.new(sub_group, Spectator::Internals::SampleValues.empty)
               end
             end
diff --git a/spec/internals/harness_spec.cr b/spec/internals/harness_spec.cr
index 9074c18..9a360c0 100644
--- a/spec/internals/harness_spec.cr
+++ b/spec/internals/harness_spec.cr
@@ -53,7 +53,6 @@ describe Spectator::Internals::Harness do
   describe "#report_expectation" do
     context "with a successful result" do
       it "stores the result" do
-        error = nil.as(Exception?)
         expectation = new_satisfied_expectation
         spy = SpyExample.create do
           harness = Spectator::Internals::Harness.current
@@ -81,7 +80,6 @@ describe Spectator::Internals::Harness do
       end
 
       it "stores the result" do
-        error = nil.as(Exception?)
         expectation = new_unsatisfied_expectation
         spy = SpyExample.create do
           harness = Spectator::Internals::Harness.current
diff --git a/spec/matchers/truthy_matcher_spec.cr b/spec/matchers/truthy_matcher_spec.cr
index 91acae9..7ef3970 100644
--- a/spec/matchers/truthy_matcher_spec.cr
+++ b/spec/matchers/truthy_matcher_spec.cr
@@ -125,7 +125,6 @@ describe Spectator::Matchers::TruthyMatcher do
 
           it "contains the \"truthy\"" do
             value = 42
-            label = "everything"
             partial = new_partial(value)
             matcher = Spectator::Matchers::TruthyMatcher.new(true)
             match_data = matcher.match(partial)
@@ -145,7 +144,6 @@ describe Spectator::Matchers::TruthyMatcher do
 
           it "contains the \"truthy\"" do
             value = 42
-            label = "everything"
             partial = new_partial(value)
             matcher = Spectator::Matchers::TruthyMatcher.new(true)
             match_data = matcher.match(partial)
@@ -261,7 +259,6 @@ describe Spectator::Matchers::TruthyMatcher do
 
           it "contains the \"falsey\"" do
             value = 42
-            label = "everything"
             partial = new_partial(value)
             matcher = Spectator::Matchers::TruthyMatcher.new(false)
             match_data = matcher.match(partial)
@@ -281,7 +278,6 @@ describe Spectator::Matchers::TruthyMatcher do
 
           it "contains the \"falsey\"" do
             value = 42
-            label = "everything"
             partial = new_partial(value)
             matcher = Spectator::Matchers::TruthyMatcher.new(false)
             match_data = matcher.match(partial)
diff --git a/spec/nested_example_group_spec.cr b/spec/nested_example_group_spec.cr
index 63d53ca..0e95838 100644
--- a/spec/nested_example_group_spec.cr
+++ b/spec/nested_example_group_spec.cr
@@ -28,7 +28,7 @@ def nested_group_with_sub_groups(sub_group_count = 5, example_count = 5)
   examples = [] of Spectator::Example
   group.children = Array(Spectator::ExampleComponent).new(sub_group_count) do |i|
     Spectator::NestedExampleGroup.new(i.to_s, group, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty).tap do |sub_group|
-      sub_group.children = Array(Spectator::ExampleComponent).new(example_count) do |j|
+      sub_group.children = Array(Spectator::ExampleComponent).new(example_count) do |_|
         PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
           examples << example
         end
@@ -359,7 +359,7 @@ describe Spectator::NestedExampleGroup do
         root = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         group = Spectator::NestedExampleGroup.new("what", root, hooks, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
@@ -378,7 +378,7 @@ describe Spectator::NestedExampleGroup do
         root = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         group = Spectator::NestedExampleGroup.new("what", root, hooks, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
@@ -397,7 +397,7 @@ describe Spectator::NestedExampleGroup do
         root = Spectator::RootExampleGroup.new(hooks, Spectator::ExampleConditions.empty)
         group = Spectator::NestedExampleGroup.new("what", root, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
@@ -416,7 +416,7 @@ describe Spectator::NestedExampleGroup do
         root = Spectator::RootExampleGroup.new(hooks, Spectator::ExampleConditions.empty)
         group = Spectator::NestedExampleGroup.new("what", root, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
diff --git a/spec/root_example_group_spec.cr b/spec/root_example_group_spec.cr
index c0528a9..9ae388e 100644
--- a/spec/root_example_group_spec.cr
+++ b/spec/root_example_group_spec.cr
@@ -22,7 +22,7 @@ def root_group_with_sub_groups(sub_group_count = 5, example_count = 5)
   examples = [] of Spectator::Example
   group.children = Array(Spectator::ExampleComponent).new(sub_group_count) do |i|
     Spectator::NestedExampleGroup.new(i.to_s, group, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty).tap do |sub_group|
-      sub_group.children = Array(Spectator::ExampleComponent).new(example_count) do |j|
+      sub_group.children = Array(Spectator::ExampleComponent).new(example_count) do |_|
         PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
           examples << example
         end
@@ -246,7 +246,7 @@ describe Spectator::RootExampleGroup do
         examples = [] of Spectator::Example
         hooks = new_hooks(after_all: ->{ called = true; nil })
         group = Spectator::RootExampleGroup.new(hooks, Spectator::ExampleConditions.empty)
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
@@ -263,7 +263,7 @@ describe Spectator::RootExampleGroup do
         examples = [] of Spectator::Example
         hooks = new_hooks(after_each: ->{ called = true; nil })
         group = Spectator::RootExampleGroup.new(hooks, Spectator::ExampleConditions.empty)
-        group.children = Array(Spectator::ExampleComponent).new(5) do |i|
+        group.children = Array(Spectator::ExampleComponent).new(5) do |_|
           PassingExample.new(group, Spectator::Internals::SampleValues.empty).tap do |example|
             examples << example
           end
diff --git a/spec/runnable_example_spec.cr b/spec/runnable_example_spec.cr
index 602dc38..5907454 100644
--- a/spec/runnable_example_spec.cr
+++ b/spec/runnable_example_spec.cr
@@ -856,7 +856,7 @@ describe Spectator::RunnableExample do
         root = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, conditions)
         group = Spectator::NestedExampleGroup.new("what", root, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        result = run_example(FailingExample, group)
+        run_example(FailingExample, group)
         called.should be_false
       end
     end
@@ -1219,7 +1219,7 @@ describe Spectator::RunnableExample do
         root = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, conditions)
         group = Spectator::NestedExampleGroup.new("what", root, Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
         root.children = [group.as(Spectator::ExampleComponent)]
-        result = run_example(ErroredExample, group)
+        run_example(ErroredExample, group)
         called.should be_false
       end
     end
diff --git a/spec/runner_spec.cr b/spec/runner_spec.cr
index 1fa678b..f3778c2 100644
--- a/spec/runner_spec.cr
+++ b/spec/runner_spec.cr
@@ -100,7 +100,7 @@ describe Spectator::Runner do
       end
 
       it "#start_example is called for each example" do
-        group = SpyExample.create_group(5) { |index| nil }
+        group = SpyExample.create_group(5) { |_| nil }
         suite = new_test_suite(group)
         spy = SpyFormatter.new
         runner = Spectator::Runner.new(suite, spectator_test_config(spy))
@@ -109,7 +109,7 @@ describe Spectator::Runner do
       end
 
       it "passes the correct example to #start_example" do
-        group = SpyExample.create_group(5) { |index| nil }
+        group = SpyExample.create_group(5) { |_| nil }
         suite = new_test_suite(group)
         spy = SpyFormatter.new
         runner = Spectator::Runner.new(suite, spectator_test_config(spy))
@@ -125,7 +125,7 @@ describe Spectator::Runner do
       end
 
       it "calls #end_example for each example" do
-        group = SpyExample.create_group(5) { |index| nil }
+        group = SpyExample.create_group(5) { |_| nil }
         suite = new_test_suite(group)
         spy = SpyFormatter.new
         runner = Spectator::Runner.new(suite, spectator_test_config(spy))
@@ -175,7 +175,7 @@ describe Spectator::Runner do
       end
 
       it "contains the expected time span" do
-        group = SpyExample.create_group(5) { |index| nil }
+        group = SpyExample.create_group(5) { |_| nil }
         suite = new_test_suite(group)
         spy = SpyFormatter.new
         runner = Spectator::Runner.new(suite, spectator_test_config(spy))
diff --git a/spec/test_suite_spec.cr b/spec/test_suite_spec.cr
index f36cbf1..24846fc 100644
--- a/spec/test_suite_spec.cr
+++ b/spec/test_suite_spec.cr
@@ -4,7 +4,7 @@ describe Spectator::TestSuite do
   describe "#each" do
     it "yields each example" do
       group = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
-      group.children = Array.new(5) do |index|
+      group.children = Array.new(5) do |_|
         PassingExample.new(group, Spectator::Internals::SampleValues.empty).as(Spectator::ExampleComponent)
       end
       test_suite = Spectator::TestSuite.new(group, Spectator::NullExampleFilter.new)
@@ -17,7 +17,7 @@ describe Spectator::TestSuite do
 
     it "skips examples not in the filter" do
       group = Spectator::RootExampleGroup.new(Spectator::ExampleHooks.empty, Spectator::ExampleConditions.empty)
-      group.children = Array.new(5) do |index|
+      group.children = Array.new(5) do |_|
         PassingExample.new(group, Spectator::Internals::SampleValues.empty).as(Spectator::ExampleComponent)
       end
       test_suite = Spectator::TestSuite.new(group, Spectator::CompositeExampleFilter.new([] of Spectator::ExampleFilter))
diff --git a/src/spectator/example_group.cr b/src/spectator/example_group.cr
index d62f7dd..42a23f3 100644
--- a/src/spectator/example_group.cr
+++ b/src/spectator/example_group.cr
@@ -95,7 +95,7 @@ module Spectator
       offset = index
       # Loop through each child
       # until one is found to contain the index.
-      child = children.each do |child|
+      found = children.each do |child|
         count = child.example_count
         # Example groups consider their range to be [0, example_count).
         # Each child is offset by the total example count of the previous children.
@@ -114,7 +114,7 @@ module Spectator
       # Otherwise, the indexer repeats the process for the next child.
       # It should be impossible to get nil here,
       # provided the bounds check and example counts are correct.
-      child.not_nil![offset]
+      found.not_nil![offset]
     end
 
     # Checks whether all examples in the group have been run.
diff --git a/src/spectator/formatting/human_time.cr b/src/spectator/formatting/human_time.cr
index e28692f..0eff947 100644
--- a/src/spectator/formatting/human_time.cr
+++ b/src/spectator/formatting/human_time.cr
@@ -35,7 +35,7 @@ module Spectator::Formatting
 
       days = hours / 24
       hours %= 24
-      return sprintf("%i days %i:%02i:%02i", days, hours, minutes, int_seconds)
+      sprintf("%i days %i:%02i:%02i", days, hours, minutes, int_seconds)
     end
   end
 end
diff --git a/src/spectator/matchers/array_matcher.cr b/src/spectator/matchers/array_matcher.cr
index e49c75b..9a7bc2e 100644
--- a/src/spectator/matchers/array_matcher.cr
+++ b/src/spectator/matchers/array_matcher.cr
@@ -11,8 +11,8 @@ module Spectator::Matchers
       values = ExpectedActual.new(expected, label, actual, partial.label)
       if values.expected.size == values.actual.size
         index = 0
-        values.expected.zip(values.actual) do |expected, actual|
-          return ContentMatchData.new(index, values) unless expected == actual
+        values.expected.zip(values.actual) do |expected, element|
+          return ContentMatchData.new(index, values) unless expected == element
           index += 1
         end
         IdenticalMatchData.new(values)