diff --git a/typst-bold-italic-diag.js b/typst-bold-italic-diag.js
new file mode 100644
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+++ b/typst-bold-italic-diag.js
@@ -0,0 +1,52 @@
+// Typst bold/italic parse-tree diagnostic
+// Open a Typst document that contains  *bold*  and  _italic_  text,
+// then paste this whole block into the browser console.
+
+(function () {
+  const strong  = [...document.querySelectorAll('.tok-strong')]
+  const emphasis = [...document.querySelectorAll('.tok-emphasis')]
+
+  console.group('=== Typst bold/italic diagnostic ===')
+
+  console.log('tok-strong  count :', strong.length)
+  console.log('tok-emphasis count:', emphasis.length)
+
+  if (strong.length) {
+    console.log('tok-strong  text  :', strong.map(s => JSON.stringify(s.textContent)))
+  }
+  if (emphasis.length) {
+    console.log('tok-emphasis text :', emphasis.map(s => JSON.stringify(s.textContent)))
+  }
+
+  // Interpret results
+  if (strong.length === 0 && emphasis.length === 0) {
+    console.warn(
+      'RESULT: Grammar is NOT producing Strong/Emphasis nodes.',
+      'This is a LALR state-merge bug — needs a grammar fix.'
+    )
+  } else {
+    const strongText  = strong.map(s => s.textContent).join('')
+    const emphText    = emphasis.map(s => s.textContent).join('')
+    const hasMidStrong  = strong.length > 2   // more than just the two * delimiters
+    const hasMidEmph    = emphasis.length > 2
+
+    if (hasMidStrong || hasMidEmph) {
+      console.info(
+        'RESULT: Grammar IS producing Strong/Emphasis nodes (content inside delimiters is styled).',
+        'Bold/italic not visible? Issue is the loaded font — Source Code Pro only has Regular (400).',
+        'Fix: switch editor font to DM Mono (which has actual Italic + Medium faces).',
+        'Or: load Source Code Pro Bold/Italic font files.'
+      )
+    } else {
+      console.warn(
+        'RESULT: Partial — only the delimiters (* or _) are styled, not the text between them.',
+        'StrongText/EmphText nodes are missing. Needs a grammar fix.'
+      )
+    }
+
+    console.log('all strong text joined :', JSON.stringify(strongText))
+    console.log('all emphasis text joined:', JSON.stringify(emphText))
+  }
+
+  console.groupEnd()
+})()