diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index b52f324..f89c555 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -14,10 +14,17 @@ before_script:
 
 spec:
   script:
-  - crystal spec
+  - crystal spec --error-on-warnings
   - bin/ameba
   - crystal tool format --check
 
+nightly:
+  image: "crystallang/crystal:nightly"
+  allow_failure: true
+  script:
+  - crystal spec --error-on-warnings
+  - crystal tool format --check
+
 pages:
   stage: deploy
   dependencies:
diff --git a/shard.yml b/shard.yml
index 77b397c..22461d6 100644
--- a/shard.yml
+++ b/shard.yml
@@ -6,7 +6,7 @@ description: |
 authors:
   - Michael Miller <icy.arctic.fox@gmail.com>
 
-crystal: 0.30.1
+crystal: 0.31.0
 
 license: MIT
 
diff --git a/spec/dsl/sample_example_group_builder_spec.cr b/spec/dsl/sample_example_group_builder_spec.cr
index 6fedcc2..a5a9d88 100644
--- a/spec/dsl/sample_example_group_builder_spec.cr
+++ b/spec/dsl/sample_example_group_builder_spec.cr
@@ -291,7 +291,7 @@ describe Spectator::DSL::SampleExampleGroupBuilder do
       factory = Spectator::DSL::ExampleFactory.new(SpyExample)
       symbol = :test
       count = 3
-      expected = Array.new(SAMPLE_VALUES_COLLECTION.size * count) { |i| SAMPLE_VALUES_COLLECTION[i / count] }
+      expected = Array.new(SAMPLE_VALUES_COLLECTION.size * count) { |i| SAMPLE_VALUES_COLLECTION[i // count] }
       create_proc = ->(s : SampleValueCollection) { s.create }
       builder = Spectator::DSL::SampleExampleGroupBuilder.new("foobar", SampleValueCollection, create_proc, "value", symbol)
       count.times { builder.add_child(factory) }
diff --git a/spec/helpers/errored_example.cr b/spec/helpers/errored_example.cr
index 7fec2e4..aa82617 100644
--- a/spec/helpers/errored_example.cr
+++ b/spec/helpers/errored_example.cr
@@ -1,17 +1,17 @@
 # Example that always raises an exception.
 class ErroredExample < Spectator::RunnableExample
   # Dummy description.
-  def what
+  def what : Symbol | String
     "ERROR"
   end
 
   # Dummy source.
-  def source
+  def source : ::Spectator::Source
     ::Spectator::Source.new(__FILE__, __LINE__)
   end
 
   # Dummy symbolic flag.
-  def symbolic?
+  def symbolic? : Bool
     false
   end
 
diff --git a/spec/helpers/failing_example.cr b/spec/helpers/failing_example.cr
index 25cd460..a0e972d 100644
--- a/spec/helpers/failing_example.cr
+++ b/spec/helpers/failing_example.cr
@@ -1,17 +1,17 @@
 # Example that always fails.
 class FailingExample < Spectator::RunnableExample
   # Dummy description.
-  def what
+  def what : Symbol | String
     "FAIL"
   end
 
   # Dummy source.
-  def source
+  def source : ::Spectator::Source
     ::Spectator::Source.new(__FILE__, __LINE__)
   end
 
   # Dummy symbolic flag.
-  def symbolic?
+  def symbolic? : Bool
     false
   end
 
diff --git a/spec/helpers/passing_example.cr b/spec/helpers/passing_example.cr
index d1e6f44..6d03aae 100644
--- a/spec/helpers/passing_example.cr
+++ b/spec/helpers/passing_example.cr
@@ -6,17 +6,17 @@ class PassingExample < Spectator::RunnableExample
   end
 
   # Dummy description.
-  def what
+  def what : Symbol | String
     "PASS"
   end
 
   # Dummy source.
-  def source
+  def source : ::Spectator::Source
     ::Spectator::Source.new(__FILE__, __LINE__)
   end
 
   # Dummy symbolic flag.
-  def symbolic?
+  def symbolic? : Bool
     @symbolic
   end
 
diff --git a/spec/helpers/spy_example.cr b/spec/helpers/spy_example.cr
index 70c256a..32b6474 100644
--- a/spec/helpers/spy_example.cr
+++ b/spec/helpers/spy_example.cr
@@ -2,17 +2,17 @@
 # This is useful for capturing what's going on when an event is running.
 class SpyExample < Spectator::RunnableExample
   # Dummy description.
-  def what
+  def what : Symbol | String
     "SPY"
   end
 
   # Dummy source.
-  def source
+  def source : ::Spectator::Source
     ::Spectator::Source.new(__FILE__, __LINE__)
   end
 
   # Dummy symbolic flag.
-  def symbolic?
+  def symbolic? : Bool
     false
   end
 
diff --git a/spec/pending_example_spec.cr b/spec/pending_example_spec.cr
index 6809816..8ed23df 100644
--- a/spec/pending_example_spec.cr
+++ b/spec/pending_example_spec.cr
@@ -1,15 +1,15 @@
 require "./spec_helper"
 
 class ConcretePendingExample < Spectator::PendingExample
-  def what
+  def what : Symbol | String
     "PENDING_TEST_EXAMPLE"
   end
 
-  def source
+  def source : ::Spectator::Source
     ::Spectator::Source.new(__FILE__, __LINE__)
   end
 
-  def symbolic?
+  def symbolic? : Bool
     false
   end
 
diff --git a/src/spectator/composite_example_filter.cr b/src/spectator/composite_example_filter.cr
index 0b1f9d3..7f776ba 100644
--- a/src/spectator/composite_example_filter.cr
+++ b/src/spectator/composite_example_filter.cr
@@ -6,7 +6,7 @@ module Spectator
     end
 
     # Checks whether the example satisfies the filter.
-    def includes?(example)
+    def includes?(example) : Bool
       @filters.any?(&.includes?(example))
     end
   end
diff --git a/src/spectator/dsl/structure_dsl.cr b/src/spectator/dsl/structure_dsl.cr
index 1957d03..bed9c59 100644
--- a/src/spectator/dsl/structure_dsl.cr
+++ b/src/spectator/dsl/structure_dsl.cr
@@ -1457,7 +1457,7 @@ module Spectator::DSL
       # Create a class derived from `RunnableExample` to run the test code.
       _spectator_example(Example%example, Test%example, ::Spectator::RunnableExample, {{what}}) do
         # Source where the example originated from.
-        def source
+        def source : ::Spectator::Source
           ::Spectator::Source.new({{_source_file}}, {{_source_line}})
         end
 
@@ -1534,7 +1534,7 @@ module Spectator::DSL
       # Create a class derived from `PendingExample` to skip the test code.
       _spectator_example(Example%example, Test%example, ::Spectator::PendingExample, {{what}}) do
         # Source where the example originated from.
-        def source
+        def source : ::Spectator::Source
           ::Spectator::Source.new({{_source_file}}, {{_source_line}})
         end
       end
@@ -1650,7 +1650,7 @@ module Spectator::DSL
         getter instance
 
         # Indicates whether the example references a method.
-        def symbolic?
+        def symbolic? : Bool
           {{what.is_a?(StringLiteral) && what.starts_with?('#') ? true : false}}
         end
 
@@ -1658,7 +1658,7 @@ module Spectator::DSL
         {{block.body}}
 
         # Description for the test.
-        def what
+        def what : String | Symbol
           {{what.is_a?(StringLiteral) ? what : what.stringify}}
         end
       end
diff --git a/src/spectator/dummy_example.cr b/src/spectator/dummy_example.cr
index 82ddcb8..62e11c9 100644
--- a/src/spectator/dummy_example.cr
+++ b/src/spectator/dummy_example.cr
@@ -10,17 +10,17 @@ module Spectator
   # This class shouldn't be used, it's just to trick the compiler.
   private class DummyExample < RunnableExample
     # Dummy description.
-    def what
+    def what : Symbol | String
       "DUMMY"
     end
 
     # Dummy symbolic flag.
-    def symbolic?
+    def symbolic? : Bool
       false
     end
 
     # Dummy source.
-    def source
+    def source : Source
       Source.new(__FILE__, __LINE__)
     end
 
diff --git a/src/spectator/example.cr b/src/spectator/example.cr
index d12363e..eee5847 100644
--- a/src/spectator/example.cr
+++ b/src/spectator/example.cr
@@ -4,8 +4,12 @@ module Spectator
   # Base class for all types of examples.
   # Concrete types must implement the `#run_impl, `#what`, `#instance`, and `#source` methods.
   abstract class Example < ExampleComponent
+    @finished = false
+
     # Indicates whether the example has already been run.
-    getter? finished = false
+    def finished? : Bool
+      @finished
+    end
 
     # Group that the example belongs to.
     getter group : ExampleGroup
@@ -36,12 +40,12 @@ module Spectator
     end
 
     # Indicates there is only one example to run.
-    def example_count
+    def example_count : Int
       1
     end
 
     # Retrieve the current example.
-    def [](index : Int)
+    def [](index : Int) : Example
       self
     end
 
diff --git a/src/spectator/example_component.cr b/src/spectator/example_component.cr
index 9c9fa95..6ac628f 100644
--- a/src/spectator/example_component.cr
+++ b/src/spectator/example_component.cr
@@ -3,7 +3,7 @@ module Spectator
   # This is used as the base node type for the composite design pattern.
   abstract class ExampleComponent
     # Text that describes the context or test.
-    abstract def what : String
+    abstract def what : Symbol | String
 
     # Indicates whether the example (or group) has been completely run.
     abstract def finished? : Bool
diff --git a/src/spectator/example_group.cr b/src/spectator/example_group.cr
index 6e25a93..0d0aa1a 100644
--- a/src/spectator/example_group.cr
+++ b/src/spectator/example_group.cr
@@ -18,6 +18,7 @@ module Spectator
     # Creates the example group.
     # The hooks are stored to be triggered later.
     def initialize(@hooks : ExampleHooks, @conditions : ExampleConditions)
+      @example_count = 0
       @before_all_hooks_run = false
       @after_all_hooks_run = false
     end
@@ -53,7 +54,9 @@ module Spectator
     end
 
     # Number of examples in this group and all sub-groups.
-    getter example_count = 0
+    def example_count : Int
+      @example_count
+    end
 
     # Retrieves an example by its index.
     # This recursively searches for an example.
@@ -118,7 +121,7 @@ module Spectator
     end
 
     # Checks whether all examples in the group have been run.
-    def finished?
+    def finished? : Bool
       children.all?(&.finished?)
     end
 
diff --git a/src/spectator/formatting/failure_junit_test_case.cr b/src/spectator/formatting/failure_junit_test_case.cr
index 964e673..99b0265 100644
--- a/src/spectator/formatting/failure_junit_test_case.cr
+++ b/src/spectator/formatting/failure_junit_test_case.cr
@@ -11,7 +11,7 @@ module Spectator::Formatting
     end
 
     # Status string specific to the result type.
-    private def status
+    private def status : String
       "FAIL"
     end
 
diff --git a/src/spectator/formatting/human_time.cr b/src/spectator/formatting/human_time.cr
index 0eff947..c7ec687 100644
--- a/src/spectator/formatting/human_time.cr
+++ b/src/spectator/formatting/human_time.cr
@@ -25,15 +25,15 @@ module Spectator::Formatting
       return "#{seconds.round(2)} seconds" if seconds < 60
 
       int_seconds = seconds.to_i
-      minutes = int_seconds / 60
+      minutes = int_seconds // 60
       int_seconds %= 60
       return sprintf("%i:%02i", minutes, int_seconds) if minutes < 60
 
-      hours = minutes / 60
+      hours = minutes // 60
       minutes %= 60
       return sprintf("%i:%02i:%02i", hours, minutes, int_seconds) if hours < 24
 
-      days = hours / 24
+      days = hours // 24
       hours %= 24
       sprintf("%i days %i:%02i:%02i", days, hours, minutes, int_seconds)
     end
diff --git a/src/spectator/formatting/skipped_junit_test_case.cr b/src/spectator/formatting/skipped_junit_test_case.cr
index 3b6ed56..6b90b4d 100644
--- a/src/spectator/formatting/skipped_junit_test_case.cr
+++ b/src/spectator/formatting/skipped_junit_test_case.cr
@@ -11,7 +11,7 @@ module Spectator::Formatting
     end
 
     # Status string specific to the result type.
-    private def status
+    private def status : String
       "TODO"
     end
 
diff --git a/src/spectator/formatting/successful_junit_test_case.cr b/src/spectator/formatting/successful_junit_test_case.cr
index b45bc87..108e966 100644
--- a/src/spectator/formatting/successful_junit_test_case.cr
+++ b/src/spectator/formatting/successful_junit_test_case.cr
@@ -9,7 +9,7 @@ module Spectator::Formatting
     end
 
     # Status string specific to the result type.
-    private def status
+    private def status : String
       "PASS"
     end
   end
diff --git a/src/spectator/line_example_filter.cr b/src/spectator/line_example_filter.cr
index 112e086..85cd739 100644
--- a/src/spectator/line_example_filter.cr
+++ b/src/spectator/line_example_filter.cr
@@ -6,7 +6,7 @@ module Spectator
     end
 
     # Checks whether the example satisfies the filter.
-    def includes?(example)
+    def includes?(example) : Bool
       @line == example.source.line
     end
   end
diff --git a/src/spectator/matchers/all_matcher.cr b/src/spectator/matchers/all_matcher.cr
index d43bda8..f413fbd 100644
--- a/src/spectator/matchers/all_matcher.cr
+++ b/src/spectator/matchers/all_matcher.cr
@@ -16,7 +16,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "all #{matcher.description}"
     end
 
diff --git a/src/spectator/matchers/array_matcher.cr b/src/spectator/matchers/array_matcher.cr
index f3c3940..314a31e 100644
--- a/src/spectator/matchers/array_matcher.cr
+++ b/src/spectator/matchers/array_matcher.cr
@@ -17,7 +17,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "contains exactly #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/attributes_matcher.cr b/src/spectator/matchers/attributes_matcher.cr
index a447d4a..93cd62a 100644
--- a/src/spectator/matchers/attributes_matcher.cr
+++ b/src/spectator/matchers/attributes_matcher.cr
@@ -20,7 +20,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "has attributes #{expected.label}"
     end
 
@@ -39,7 +39,7 @@ module Spectator::Matchers
     def negated_match(actual : TestExpression(T)) : MatchData forall T
       snapshot = snapshot_values(actual.value)
       if match?(snapshot)
-        FailedMatchData.new("#{actual.label} has attributes #{expected.label}", **values(snapshot))
+        FailedMatchData.new("#{actual.label} has attributes #{expected.label}", **negated_values(snapshot))
       else
         SuccessfulMatchData.new
       end
@@ -79,5 +79,17 @@ module Spectator::Matchers
       }
       {% end %}
     end
+
+    # Produces the tuple for the failed negated match data from a snapshot of the attributes.
+    private def negated_values(snapshot)
+      {% begin %}
+      {
+        {% for attribute in ExpectedType.keys %}
+        {{"expected " + attribute.stringify}}: "Not #{expected.value[{{attribute.symbolize}}].inspect}",
+        {{"actual " + attribute.stringify}}:   snapshot[{{attribute.symbolize}}].inspect,
+        {% end %}
+      }
+      {% end %}
+    end
   end
 end
diff --git a/src/spectator/matchers/case_matcher.cr b/src/spectator/matchers/case_matcher.cr
index 3ba55f3..e7f0891 100644
--- a/src/spectator/matchers/case_matcher.cr
+++ b/src/spectator/matchers/case_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "matches #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value === actual.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not match #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} matched #{expected.label}"
     end
   end
diff --git a/src/spectator/matchers/change_exact_matcher.cr b/src/spectator/matchers/change_exact_matcher.cr
index 48dcf9f..7245386 100644
--- a/src/spectator/matchers/change_exact_matcher.cr
+++ b/src/spectator/matchers/change_exact_matcher.cr
@@ -21,7 +21,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "changes #{expression.label} from #{expected_before.inspect} to #{expected_after.inspect}"
     end
 
diff --git a/src/spectator/matchers/change_from_matcher.cr b/src/spectator/matchers/change_from_matcher.cr
index 82a9267..cafb51d 100644
--- a/src/spectator/matchers/change_from_matcher.cr
+++ b/src/spectator/matchers/change_from_matcher.cr
@@ -19,7 +19,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "changes #{expression.label} from #{expected}"
     end
 
diff --git a/src/spectator/matchers/change_matcher.cr b/src/spectator/matchers/change_matcher.cr
index ad8ca89..2b016d5 100644
--- a/src/spectator/matchers/change_matcher.cr
+++ b/src/spectator/matchers/change_matcher.cr
@@ -17,7 +17,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "changes #{expression.label}"
     end
 
diff --git a/src/spectator/matchers/change_relative_matcher.cr b/src/spectator/matchers/change_relative_matcher.cr
index adb4cdc..2f170eb 100644
--- a/src/spectator/matchers/change_relative_matcher.cr
+++ b/src/spectator/matchers/change_relative_matcher.cr
@@ -17,7 +17,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "changes #{expression.label} #{@relativity}"
     end
 
diff --git a/src/spectator/matchers/change_to_matcher.cr b/src/spectator/matchers/change_to_matcher.cr
index 65f1ce5..a05587a 100644
--- a/src/spectator/matchers/change_to_matcher.cr
+++ b/src/spectator/matchers/change_to_matcher.cr
@@ -19,7 +19,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "changes #{expression.label} to #{expected}"
     end
 
diff --git a/src/spectator/matchers/collection_matcher.cr b/src/spectator/matchers/collection_matcher.cr
index bfa88f2..44f2ee8 100644
--- a/src/spectator/matchers/collection_matcher.cr
+++ b/src/spectator/matchers/collection_matcher.cr
@@ -8,12 +8,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is in #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value.includes?(actual.value)
     end
 
@@ -23,7 +23,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not in #{expected.label}"
     end
 
@@ -34,7 +34,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is in #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/contain_matcher.cr b/src/spectator/matchers/contain_matcher.cr
index 53389fc..26d3287 100644
--- a/src/spectator/matchers/contain_matcher.cr
+++ b/src/spectator/matchers/contain_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "contains #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value.all? do |item|
         actual.value.includes?(item)
       end
@@ -24,7 +24,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not match #{expected.label}"
     end
 
@@ -35,7 +35,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} contains #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/empty_matcher.cr b/src/spectator/matchers/empty_matcher.cr
index a8ccfe9..c64c6d7 100644
--- a/src/spectator/matchers/empty_matcher.cr
+++ b/src/spectator/matchers/empty_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is empty"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value.empty?
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not empty"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is empty"
     end
   end
diff --git a/src/spectator/matchers/end_with_matcher.cr b/src/spectator/matchers/end_with_matcher.cr
index ed76381..cc28e9a 100644
--- a/src/spectator/matchers/end_with_matcher.cr
+++ b/src/spectator/matchers/end_with_matcher.cr
@@ -17,7 +17,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "ends with #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/equality_matcher.cr b/src/spectator/matchers/equality_matcher.cr
index 5d58454..bcdcd44 100644
--- a/src/spectator/matchers/equality_matcher.cr
+++ b/src/spectator/matchers/equality_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "equals #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value == actual.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not equal #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} equals #{expected.label}"
     end
   end
diff --git a/src/spectator/matchers/exception_matcher.cr b/src/spectator/matchers/exception_matcher.cr
index 981845c..6455df5 100644
--- a/src/spectator/matchers/exception_matcher.cr
+++ b/src/spectator/matchers/exception_matcher.cr
@@ -21,7 +21,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       if (message = @expected)
         "raises #{ExceptionType} with message #{message}"
       else
diff --git a/src/spectator/matchers/failed_match_data.cr b/src/spectator/matchers/failed_match_data.cr
index f1925ce..3e0857a 100644
--- a/src/spectator/matchers/failed_match_data.cr
+++ b/src/spectator/matchers/failed_match_data.cr
@@ -4,7 +4,7 @@ module Spectator::Matchers
   # Information about a failed match.
   struct FailedMatchData < MatchData
     # Indicates that the match failed.
-    def matched?
+    def matched? : Bool
       false
     end
 
diff --git a/src/spectator/matchers/greater_than_equal_matcher.cr b/src/spectator/matchers/greater_than_equal_matcher.cr
index 5f4e20b..08eb88c 100644
--- a/src/spectator/matchers/greater_than_equal_matcher.cr
+++ b/src/spectator/matchers/greater_than_equal_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "greater than or equal to #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value >= expected.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is less than #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is greater than or equal to #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/greater_than_matcher.cr b/src/spectator/matchers/greater_than_matcher.cr
index c51303b..5dfc90c 100644
--- a/src/spectator/matchers/greater_than_matcher.cr
+++ b/src/spectator/matchers/greater_than_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "greater than #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value > expected.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is less than or equal to #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is greater than #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/have_key_matcher.cr b/src/spectator/matchers/have_key_matcher.cr
index e3f2560..c579930 100644
--- a/src/spectator/matchers/have_key_matcher.cr
+++ b/src/spectator/matchers/have_key_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "has key #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value.has_key?(expected.value)
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not have key #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} has key #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/have_matcher.cr b/src/spectator/matchers/have_matcher.cr
index 5dd0151..d67eb35 100644
--- a/src/spectator/matchers/have_matcher.cr
+++ b/src/spectator/matchers/have_matcher.cr
@@ -8,12 +8,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "includes #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       if (value = actual.value).is_a?(String)
         match_string?(value)
       else
@@ -46,7 +46,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not include #{expected.label}"
     end
 
@@ -57,7 +57,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} includes #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/have_predicate_matcher.cr b/src/spectator/matchers/have_predicate_matcher.cr
index dedc70e..93bcca6 100644
--- a/src/spectator/matchers/have_predicate_matcher.cr
+++ b/src/spectator/matchers/have_predicate_matcher.cr
@@ -17,7 +17,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "has #{expected.label}"
     end
 
@@ -48,7 +48,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not have #{expected.label}"
     end
 
@@ -59,7 +59,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} has #{expected.label}"
     end
 
@@ -76,7 +76,7 @@ module Spectator::Matchers
     end
 
     # Checks if all predicate methods from the snapshot of them are satisified.
-    private def match?(snapshot)
+    private def match?(snapshot) : Bool
       # Test each predicate and immediately return false if one is false.
       {% for attribute in ExpectedType.keys %}
       return false unless snapshot[{{attribute.symbolize}}]
diff --git a/src/spectator/matchers/have_value_matcher.cr b/src/spectator/matchers/have_value_matcher.cr
index 9c722f5..1f3e4a9 100644
--- a/src/spectator/matchers/have_value_matcher.cr
+++ b/src/spectator/matchers/have_value_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "has value #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value.has_value?(expected.value)
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not have value #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} has value #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/inequality_matcher.cr b/src/spectator/matchers/inequality_matcher.cr
index 7f175f1..f721ab4 100644
--- a/src/spectator/matchers/inequality_matcher.cr
+++ b/src/spectator/matchers/inequality_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is not equal to #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value != actual.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is equal to #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is not equal to #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/less_than_equal_matcher.cr b/src/spectator/matchers/less_than_equal_matcher.cr
index 900c7a4..bc56dab 100644
--- a/src/spectator/matchers/less_than_equal_matcher.cr
+++ b/src/spectator/matchers/less_than_equal_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "less than or equal to #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value <= expected.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is greater than #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is less than or equal to #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/less_than_matcher.cr b/src/spectator/matchers/less_than_matcher.cr
index 5f2ec2c..4e14cd4 100644
--- a/src/spectator/matchers/less_than_matcher.cr
+++ b/src/spectator/matchers/less_than_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "less than #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value < expected.value
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is greater than or equal to #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is less than #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/nil_matcher.cr b/src/spectator/matchers/nil_matcher.cr
index 343fe79..5334037 100644
--- a/src/spectator/matchers/nil_matcher.cr
+++ b/src/spectator/matchers/nil_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is nil"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value.nil?
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not nil"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is nil"
     end
   end
diff --git a/src/spectator/matchers/predicate_matcher.cr b/src/spectator/matchers/predicate_matcher.cr
index 46d3d94..5c43c60 100644
--- a/src/spectator/matchers/predicate_matcher.cr
+++ b/src/spectator/matchers/predicate_matcher.cr
@@ -16,7 +16,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is #{expected.label}"
     end
 
@@ -47,7 +47,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not #{expected.label}"
     end
 
@@ -58,7 +58,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/range_matcher.cr b/src/spectator/matchers/range_matcher.cr
index 6eba568..32d491f 100644
--- a/src/spectator/matchers/range_matcher.cr
+++ b/src/spectator/matchers/range_matcher.cr
@@ -7,7 +7,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is in #{expected.label}"
     end
 
@@ -26,7 +26,7 @@ module Spectator::Matchers
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value.includes?(actual.value)
     end
 
@@ -36,7 +36,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not in #{expected.label} (#{exclusivity})"
     end
 
@@ -47,7 +47,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is in #{expected.label} (#{exclusivity})"
     end
 
diff --git a/src/spectator/matchers/reference_matcher.cr b/src/spectator/matchers/reference_matcher.cr
index 633e619..3586e14 100644
--- a/src/spectator/matchers/reference_matcher.cr
+++ b/src/spectator/matchers/reference_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value.same?(actual.value)
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is #{expected.label}"
     end
   end
diff --git a/src/spectator/matchers/respond_matcher.cr b/src/spectator/matchers/respond_matcher.cr
index d842167..ce69a7e 100644
--- a/src/spectator/matchers/respond_matcher.cr
+++ b/src/spectator/matchers/respond_matcher.cr
@@ -9,7 +9,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "responds to #{label}"
     end
 
diff --git a/src/spectator/matchers/size_matcher.cr b/src/spectator/matchers/size_matcher.cr
index 1ab6e3d..d309849 100644
--- a/src/spectator/matchers/size_matcher.cr
+++ b/src/spectator/matchers/size_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "has size #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value == actual.value.size
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} does not have #{expected.label} elements"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} has #{expected.label} elements"
     end
 
diff --git a/src/spectator/matchers/size_of_matcher.cr b/src/spectator/matchers/size_of_matcher.cr
index 3e9f1cf..0d7bc30 100644
--- a/src/spectator/matchers/size_of_matcher.cr
+++ b/src/spectator/matchers/size_of_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is the same size as #{expected.label}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       expected.value.size == actual.value.size
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not the same size as #{expected.label}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is the same size as #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/start_with_matcher.cr b/src/spectator/matchers/start_with_matcher.cr
index 067f52a..29da717 100644
--- a/src/spectator/matchers/start_with_matcher.cr
+++ b/src/spectator/matchers/start_with_matcher.cr
@@ -16,7 +16,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "starts with #{expected.label}"
     end
 
diff --git a/src/spectator/matchers/successful_match_data.cr b/src/spectator/matchers/successful_match_data.cr
index 25a94ce..29b11d0 100644
--- a/src/spectator/matchers/successful_match_data.cr
+++ b/src/spectator/matchers/successful_match_data.cr
@@ -4,7 +4,7 @@ module Spectator::Matchers
   # Information about a successful match.
   struct SuccessfulMatchData < MatchData
     # Indicates that the match succeeded.
-    def matched?
+    def matched? : Bool
       true
     end
   end
diff --git a/src/spectator/matchers/truthy_matcher.cr b/src/spectator/matchers/truthy_matcher.cr
index 34aea3b..df21d8c 100644
--- a/src/spectator/matchers/truthy_matcher.cr
+++ b/src/spectator/matchers/truthy_matcher.cr
@@ -18,7 +18,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is #{label}"
     end
 
@@ -83,7 +83,7 @@ module Spectator::Matchers
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       @truthy == !!actual.value
     end
 
@@ -93,7 +93,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is #{negated_label}"
     end
 
@@ -104,7 +104,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is #{label}"
     end
 
diff --git a/src/spectator/matchers/type_matcher.cr b/src/spectator/matchers/type_matcher.cr
index 2b44296..4b7aff3 100644
--- a/src/spectator/matchers/type_matcher.cr
+++ b/src/spectator/matchers/type_matcher.cr
@@ -7,12 +7,12 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "is as #{Expected}"
     end
 
     # Checks whether the matcher is satisifed with the expression given to it.
-    private def match?(actual : TestExpression(T)) forall T
+    private def match?(actual : TestExpression(T)) : Bool forall T
       actual.value.is_a?(Expected)
     end
 
@@ -22,7 +22,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message(actual)
+    private def failure_message(actual) : String
       "#{actual.label} is not a #{Expected}"
     end
 
@@ -33,7 +33,7 @@ module Spectator::Matchers
     #
     # The message should typically only contain the test expression labels.
     # Actual values should be returned by `#values`.
-    private def failure_message_when_negated(actual)
+    private def failure_message_when_negated(actual) : String
       "#{actual.label} is a #{Expected}"
     end
 
diff --git a/src/spectator/matchers/unordered_array_matcher.cr b/src/spectator/matchers/unordered_array_matcher.cr
index 823ee16..5bbbdf1 100644
--- a/src/spectator/matchers/unordered_array_matcher.cr
+++ b/src/spectator/matchers/unordered_array_matcher.cr
@@ -14,7 +14,7 @@ module Spectator::Matchers
     # Short text about the matcher's purpose.
     # This explains what condition satisfies the matcher.
     # The description is used when the one-liner syntax is used.
-    def description
+    def description : String
       "contains #{expected.label} in any order"
     end
 
diff --git a/src/spectator/name_example_filter.cr b/src/spectator/name_example_filter.cr
index 8ec6409..a90560c 100644
--- a/src/spectator/name_example_filter.cr
+++ b/src/spectator/name_example_filter.cr
@@ -6,7 +6,7 @@ module Spectator
     end
 
     # Checks whether the example satisfies the filter.
-    def includes?(example)
+    def includes?(example) : Bool
       @name == example.to_s
     end
   end
diff --git a/src/spectator/nested_example_group.cr b/src/spectator/nested_example_group.cr
index 0a90b86..386b0f4 100644
--- a/src/spectator/nested_example_group.cr
+++ b/src/spectator/nested_example_group.cr
@@ -23,7 +23,7 @@ module Spectator
     end
 
     # Indicates wheter the group references a type.
-    def symbolic?
+    def symbolic? : Bool
       @what.is_a?(Symbol)
     end
 
diff --git a/src/spectator/null_example_filter.cr b/src/spectator/null_example_filter.cr
index b23e4ac..5a3e036 100644
--- a/src/spectator/null_example_filter.cr
+++ b/src/spectator/null_example_filter.cr
@@ -2,7 +2,7 @@ module Spectator
   # Filter that matches all examples.
   class NullExampleFilter < ExampleFilter
     # Checks whether the example satisfies the filter.
-    def includes?(example)
+    def includes?(example) : Bool
       true
     end
   end
diff --git a/src/spectator/pending_example.cr b/src/spectator/pending_example.cr
index f485ec4..897b134 100644
--- a/src/spectator/pending_example.cr
+++ b/src/spectator/pending_example.cr
@@ -5,7 +5,7 @@ module Spectator
   # This class will not run example code.
   abstract class PendingExample < Example
     # Returns a pending result.
-    private def run_impl
+    private def run_impl : Result
       PendingResult.new(self)
     end
   end
diff --git a/src/spectator/root_example_group.cr b/src/spectator/root_example_group.cr
index f169064..65836c3 100644
--- a/src/spectator/root_example_group.cr
+++ b/src/spectator/root_example_group.cr
@@ -5,12 +5,12 @@ module Spectator
   # The root has no parent.
   class RootExampleGroup < ExampleGroup
     # Dummy value - this should never be used.
-    def what
+    def what : Symbol | String
       "ROOT"
     end
 
     # Indicates that the group is symbolic.
-    def symbolic?
+    def symbolic? : Bool
       true
     end
 
diff --git a/src/spectator/runnable_example.cr b/src/spectator/runnable_example.cr
index 2879cb1..95b1c41 100644
--- a/src/spectator/runnable_example.cr
+++ b/src/spectator/runnable_example.cr
@@ -8,7 +8,7 @@ module Spectator
   abstract class RunnableExample < Example
     # Runs the example, hooks, and captures the result
     # and translates to a usable result.
-    def run_impl
+    def run_impl : Result
       result = capture_result
       expectations = Internals::Harness.current.expectations
       translate_result(result, expectations)
diff --git a/src/spectator/source_example_filter.cr b/src/spectator/source_example_filter.cr
index 6eaec5f..d3ad4dc 100644
--- a/src/spectator/source_example_filter.cr
+++ b/src/spectator/source_example_filter.cr
@@ -7,7 +7,7 @@ module Spectator
     end
 
     # Checks whether the example satisfies the filter.
-    def includes?(example)
+    def includes?(example) : Bool
       @source === example.source
     end
   end