diff --git a/js/bio.tools.api.js b/js/bio.tools.api.js
index 98c865fb..ab09260b 100644
--- a/js/bio.tools.api.js
+++ b/js/bio.tools.api.js
@@ -39,6 +39,7 @@ function biotool_api(){
         // run pusher, fill queue with all the elements
         pusher(node);
         job_length+=queue.length;
+        // create a callback caller that sum all descendant usage and call the actual callback
         function call_callback(){
             var total=0;
             $.each(queue,function(i,e){