diff --git a/gui/main.qml b/gui/main.qml
index aadc675..362839c 100644
--- a/gui/main.qml
+++ b/gui/main.qml
@@ -622,7 +622,7 @@ ApplicationWindow {
             Text {
                 id: callText
                 Layout.fillWidth: true
-                text: visible ? chatModel.prettyJson(block.blockContent || "") : ""
+                text: visible ? chatModel.prettyJson(String(block.blockContent || "")) : ""
                 textFormat: Text.RichText
                 wrapMode: Text.Wrap
                 font.family: "monospace"
@@ -653,12 +653,12 @@ ApplicationWindow {
                 Layout.fillWidth: true
                 text: {
                     if (!visible) return ""
-                    let content = block.blockContent || ""
+                    let content = String(block.blockContent || "")
                     if (!content) return ""
                     let trimmed = content.trim()
-                    if (trimmed.startsWith("{") || trimmed.startsWith("["))
+                    if (trimmed.charAt(0) === '{' || trimmed.charAt(0) === '[')
                         return chatModel.prettyJson(content)
-                    if (trimmed.startsWith("---") || trimmed.startsWith("diff "))
+                    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>')
                 }