diff --git a/gui/chatblockmodel.cpp b/gui/chatblockmodel.cpp
index f71dd4a..2908651 100644
--- a/gui/chatblockmodel.cpp
+++ b/gui/chatblockmodel.cpp
@@ -61,6 +61,25 @@ QVariant ChatBlockModel::data(const QModelIndex &index, int role) const
             block.cachedContent = block.content;
         }
         return block.cachedSubBlocks;
+    case FormattedContentRole: {
+        // For call blocks: always pretty-print JSON
+        // For tool blocks: detect JSON/diff, format accordingly
+        // For others: just escape HTML
+        QString content = block.content;
+        if (content.isEmpty()) return QString();
+        if (block.type == ChatBlock::Call) {
+            return prettyJson(content);
+        }
+        QString trimmed = content.trimmed();
+        if (trimmed.startsWith('{') || trimmed.startsWith('[')) {
+            return prettyJson(content);
+        }
+        if (trimmed.startsWith(QLatin1String("---")) || trimmed.startsWith(QLatin1String("diff "))) {
+            return highlightedHtml(content, QStringLiteral("Diff"));
+        }
+        // Plain text: escape and add line breaks
+        return content.toHtmlEscaped().replace('\n', QLatin1String("<br>"));
+    }
     }
     return {};
 }
@@ -72,6 +91,7 @@ QHash<int, QByteArray> ChatBlockModel::roleNames() const
         {NameRole, "blockName"},
         {ContentRole, "blockContent"},
         {SubBlocksRole, "subBlocks"},
+        {FormattedContentRole, "formattedContent"},
     };
 }
 
diff --git a/gui/chatblockmodel.h b/gui/chatblockmodel.h
index 5bbb823..f5d660a 100644
--- a/gui/chatblockmodel.h
+++ b/gui/chatblockmodel.h
@@ -48,6 +48,7 @@ public:
         NameRole,
         ContentRole,
         SubBlocksRole,  // QVariantList of sub-block maps
+        FormattedContentRole, // pre-formatted HTML for call/tool expanded view
     };
 
     explicit ChatBlockModel(QObject *parent = nullptr);
diff --git a/gui/main.qml b/gui/main.qml
index 4d6e426..e74c8cc 100644
--- a/gui/main.qml
+++ b/gui/main.qml
@@ -624,7 +624,7 @@ ApplicationWindow {
             Text {
                 id: callText
                 Layout.fillWidth: true
-                text: visible ? chatModel.prettyJson(String(block.blockContent || "")) : ""
+                text: block.formattedContent || ""
                 textFormat: Text.RichText
                 wrapMode: Text.Wrap
                 font.family: "monospace"
@@ -653,17 +653,7 @@ ApplicationWindow {
             Text {
                 id: toolText
                 Layout.fillWidth: true
-                text: {
-                    if (!visible) return ""
-                    let content = String(block.blockContent || "")
-                    if (!content) return ""
-                    let trimmed = content.trim()
-                    if (trimmed.charAt(0) === '{' || trimmed.charAt(0) === '[')
-                        return chatModel.prettyJson(content)
-                    if (trimmed.indexOf("---") === 0 || trimmed.indexOf("diff ") === 0)
-                        return chatModel.highlightedHtml(content, "diff")
-                    return content.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/\n/g, '<br>')
-                }
+                text: block.formattedContent || ""
                 textFormat: Text.RichText
                 wrapMode: Text.Wrap
                 font.family: "monospace"