diff --git a/tensor2tensor/insights/README.md b/tensor2tensor/insights/README.md
index 014bfca81..65ca95d59 100644
--- a/tensor2tensor/insights/README.md
+++ b/tensor2tensor/insights/README.md
@@ -42,14 +42,14 @@ Start guide, a sample configuration would be:
         "hparams": "",
         "hparams_set": "transformer_base_single_gpu",
         "problem": "translate_ende_wmt32k"
-      },
-    }]
+      }
+    }],
     "language": [{
       "code": "en",
-      "name": "English",
+      "name": "English"
     },{
       "code": "de",
-      "name": "German",
+      "name": "German"
     }]
   }
 ```
diff --git a/tensor2tensor/insights/polymer/explore_view/explore-view.html b/tensor2tensor/insights/polymer/explore_view/explore-view.html
index f74715016..9d40ea551 100644
--- a/tensor2tensor/insights/polymer/explore_view/explore-view.html
+++ b/tensor2tensor/insights/polymer/explore_view/explore-view.html
@@ -150,5 +150,6 @@ <h4>Rapid Response</h4>
       on-response="handleTranslationResponse_">
     </iron-ajax>
   </template>
+  <script src="../d3/d3.js"></script>
   <script src="explore-view.js"></script>
 </dom-module>
diff --git a/tensor2tensor/insights/server.py b/tensor2tensor/insights/server.py
index 54421db58..c0a1f7089 100644
--- a/tensor2tensor/insights/server.py
+++ b/tensor2tensor/insights/server.py
@@ -20,6 +20,8 @@
 from flask import jsonify
 from flask import request
 from flask import send_from_directory
+from flask.json import JSONEncoder
+import numpy as np
 from gunicorn.app.base import BaseApplication
 from gunicorn.six import iteritems
 from tensor2tensor.insights import transformer_model
@@ -36,6 +38,23 @@
                     "Path to static javascript and html files to serve.")
 
 
+_NUMPY_INT_DTYPES = [
+  np.int8, np.int16, np.int32, np.int64
+]
+_NUMPY_FP_DTYPES = [
+  np.float16, np.float32, np.float64
+]
+class NumpySerializationFix(JSONEncoder):
+  """json module cannot serialize numpy datatypes, reinterpret them first"""
+  def default(self, obj):
+    obj_type = type(obj)
+    if obj_type in _NUMPY_INT_DTYPES:
+      return int(obj)
+    if obj_type in _NUMPY_FP_DTYPES:
+      return float(obj)
+    return json.JSONEncoder.default(self, obj)
+
+
 class DebugFrontendApplication(BaseApplication):
   """A local custom application for GUnicorns.
 
@@ -100,6 +119,7 @@ def main(_):
       __name__.split(".")[0],
       static_url_path="/polymer",
       static_folder=FLAGS.static_path)
+  app.json_encoder = NumpySerializationFix
 
   # Disable static file caching.
   app.config["SEND_FILE_MAX_AGE_DEFAULT"] = 0
@@ -112,7 +132,7 @@ def language_list():  # pylint: disable=unused-variable
       JSON for the languages.
     """
     return jsonify({
-        "language": languages.values()
+        "language": list(languages.values())
     })
 
   @app.route("/api/list_models/")