diff --git a/internal/store_lookup.go b/internal/store_lookup.go
new file mode 100644
index 0000000..18c8e13
--- /dev/null
+++ b/internal/store_lookup.go
@@ -0,0 +1,10 @@
+package internal
+
+// Exists reports whether key is present in the store, without allocating a
+// value copy -- useful for existence checks ahead of a Set/Delete.
+func (s *Store) Exists(key string) bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	_, ok := s.data[key]
+	return ok
+}