diff --git a/lib_vector_search/include/bucket_finder.h b/lib_vector_search/include/bucket_finder.h
index b97ecbc..784705e 100644
--- a/lib_vector_search/include/bucket_finder.h
+++ b/lib_vector_search/include/bucket_finder.h
@@ -5,6 +5,12 @@
 
 #include <unordered_map>
 
+/** A Bucket contains a partial WordRefList, split-up and (hash-)mapped by their
+ * first characters.
+ *
+ * It's meant to be read and written by a single thread without the need for
+ * synchronization.
+ */
 class Bucket {
 private:
   std::unordered_map<char, WordRefList> directory_;