diff --git a/src/spectator/config.cr b/src/spectator/config.cr
index efbdb6a..66e6501 100644
--- a/src/spectator/config.cr
+++ b/src/spectator/config.cr
@@ -3,6 +3,7 @@ require "./node_filter"
 require "./example_group"
 require "./filtered_example_iterator"
 require "./formatting/formatter"
+require "./node_iterator"
 require "./run_flags"
 
 module Spectator
@@ -23,6 +24,9 @@ module Spectator
     # Filter used to select which examples to _not_ run.
     getter node_reject : NodeFilter
 
+    # Tags to filter on if they're present in a spec.
+    protected getter match_filters : Metadata
+
     # List of hooks to run before all examples in the test suite.
     protected getter before_suite_hooks : Deque(ExampleGroupHook)
 
@@ -53,6 +57,7 @@ module Spectator
       @random_seed = source.random_seed
       @node_filter = source.node_filter
       @node_reject = source.node_reject
+      @match_filters = source.match_filters
 
       @before_suite_hooks = source.before_suite_hooks
       @before_all_hooks = source.before_all_hooks
@@ -90,7 +95,20 @@ module Spectator
 
     # Creates an iterator configured to select the filtered examples.
     def iterator(group : ExampleGroup)
-      FilteredExampleIterator.new(group, @node_filter).reject(@node_reject)
+      match_filter = match_filter(group)
+      iterator = FilteredExampleIterator.new(group, @node_filter)
+      iterator = iterator.select(match_filter) if match_filter
+      iterator.reject(@node_reject)
+    end
+
+    # Creates a node filter if any conditionally matching filters apply to an example group.
+    private def match_filter(group : ExampleGroup) : NodeFilter?
+      iterator = NodeIterator.new(group)
+      filters = @match_filters.compact_map do |key, value|
+        filter = TagNodeFilter.new(key.to_s, value)
+        filter.as(NodeFilter) if iterator.rewind.any?(filter)
+      end
+      CompositeNodeFilter.new(filters) unless filters.empty?
     end
 
     # Retrieves the configured random number generator.
diff --git a/src/spectator/config/builder.cr b/src/spectator/config/builder.cr
index 522734f..7866fc6 100644
--- a/src/spectator/config/builder.cr
+++ b/src/spectator/config/builder.cr
@@ -1,6 +1,7 @@
 require "../composite_node_filter"
 require "../node_filter"
 require "../formatting"
+require "../metadata"
 require "../null_node_filter"
 require "../run_flags"
 require "../tag_node_filter"
@@ -17,6 +18,8 @@ module Spectator
       # Toggles indicating how the test spec should execute.
       property run_flags = RunFlags::None
 
+      protected getter match_filters : Metadata = {:focus => nil.as(String?)}
+
       @primary_formatter : Formatting::Formatter?
       @additional_formatters = [] of Formatting::Formatter
       @filters = [] of NodeFilter
@@ -282,6 +285,12 @@ module Spectator
         values.each { |tag, value| @rejects << TagNodeFilter.new(tag, value.to_s) }
       end
 
+      # Specifies one or more tags to filter on only if they're present in the spec.
+      def filter_run_when_matching(*tags : Symbol, **values)
+        tags.each { |tag| @match_filters[tag] = nil }
+        values.each { |tag, value| @match_filters[tag] = value.to_s }
+      end
+
       # Retrieves a filter that determines which examples can run.
       # If no filters were added with `#add_node_filter`,
       # then the returned filter will allow all examples to be run.