diff --git a/catalog/common/models.py b/catalog/common/models.py
index e020f3f6..564f5bce 100644
--- a/catalog/common/models.py
+++ b/catalog/common/models.py
@@ -736,7 +736,7 @@ class Item(PolymorphicModel):
                 if not getattr(self, k) or ignore_existing_content:
                     setattr(self, k, v)
                 elif k in self.METADATA_MERGE_LIST:
-                    setattr(self, k, uniq((v or []) + getattr(self, k, [])))
+                    setattr(self, k, uniq(getattr(self, k, []) + (v or [])))
         if p.cover and (not self.has_cover() or ignore_existing_content):
             self.cover = p.cover
 
diff --git a/catalog/templates/catalog_history.html b/catalog/templates/catalog_history.html
index bd090cea..32496156 100644
--- a/catalog/templates/catalog_history.html
+++ b/catalog/templates/catalog_history.html
@@ -21,16 +21,43 @@
       main>div {
         margin-bottom: 4rem;
       }
+
+      /* diff viewer */
+      .diffview pre {
+        white-space: pre-wrap;
+        word-wrap: break-word;
+        word-break: break-all;
+        background: unset;
+      }
+      .diffview td {
+        vertical-align: top;
+      }
+      .diffview td div{
+        display: none;
+      }
     </style>
+    <script src="{{ cdn_url }}/npm/json5@2.2.3/dist/index.min.js"></script>
+    <script type="text/javascript">
+    function parse_json(j){
+      try {
+        j = JSON5.parse(j);
+      } catch (e) {
+        if (j == 'None' || j == '-' || j == '') j = undefined;
+        if (j == 'True') j = true;
+        if (j == 'False') j = false;
+      }
+      return JSON.stringify(j, null, 2);
+    }
+    </script>
   </head>
   <body>
     {% include "_header.html" %}
     <main>
       <div class="grid__main">
         <h4>{{ item.display_title }} - {% trans "revision history" %}</h4>
-        <table class="table table-striped table-bordered">
+        <table class="diffview">
           <thead>
-            <tr style="background:#eee;">
+            <tr>
               <th>Field</th>
               <th style="width:40%;">From</th>
               <th style="width:40%;">To</th>
@@ -42,7 +69,7 @@
                 <td colspan="3">
                   <b title="#{{ log.id }}">
                     {% if request.user.is_staff or log.actor.preference.show_last_edit %}
-                      {{ log.actor.username }}
+                      {{ log.actor.username|default:'-' }}
                     {% else %}
                       <i class="fa-solid fa-user-secret"></i>
                     {% endif %}
@@ -51,10 +78,16 @@
                 </td>
               </tr>
               {% for key, value in log.changes_dict.items %}
-                <tr {% cycle 'style="background:#eee;"' '' %}>
+                <tr>
                   <td>{{ key }}</td>
-                  <td>{{ value.0|default:"-" }}</td>
-                  <td>{{ value.1|default:"-" }}</td>
+                  <td _='init set x to innerText of first in me then set innerHTML of last in me to parse_json(x)'>
+                    <div class="hidden">{{ value.0|default:"-" }}</div>
+                    <pre></pre>
+                  </td>
+                  <td _='init set x to innerText of first in me then set innerHTML of last in me to parse_json(x)'>
+                    <div class="hidden">{{ value.1|default:"-" }}</div>
+                    <pre></pre>
+                  </td>
                 </tr>
               {% empty %}
                 <tr>

Field	From	To	{% if request.user.is_staff or log.actor.preference.show_last_edit %} - {{ log.actor.username }} + {{ log.actor.username\|default:'-' }} {% else %} {% endif %} @@ -51,10 +78,16 @@
{{ key }}	{{ value.0\|default:"-" }}	{{ value.1\|default:"-" }}	+ {{ value.0\|default:"-" }} + +	+ {{ value.1\|default:"-" }} + +