diff --git a/diagnostic-typst.js b/diagnostic-typst.js
new file mode 100644
index 0000000000..73f5a83af6
--- /dev/null
+++ b/diagnostic-typst.js
@@ -0,0 +1,53 @@
+/**
+ * Typst syntax highlighting diagnostics.
+ * Paste this entire file into the browser dev tools console
+ * while a Typst file is open in the editor.
+ */
+
+// 1. Find the active CodeMirror editor view
+const view = [...document.querySelectorAll('.cm-editor')]
+  .map(el => el.cmView?.view)
+  .find(Boolean)
+
+if (!view) {
+  console.error('No CodeMirror view found — make sure a file is open in the editor')
+} else {
+  // 2. Show the language currently active
+  const lang = view.state.facet(
+    window.CM?.language?.language ?? view.state.facet.constructor
+  )
+  console.log('Language:', view.state.languageDataAt('commentTokens', 0))
+
+  // 3. Print the top of the parse tree (first 800 chars)
+  const tree = view.state.tree
+  console.log('Parse tree (top):\n' + tree.toString().slice(0, 800))
+
+  // 4. Walk the first 20 leaf nodes and show their type + text
+  console.log('\nFirst 20 leaf nodes:')
+  let count = 0
+  tree.iterate({
+    enter(node) {
+      if (node.firstChild) return  // skip non-leaf
+      if (count++ >= 20) return false
+      const text = view.state.doc.sliceString(node.from, node.to)
+      console.log(`  [${node.name}] ${JSON.stringify(text.slice(0, 40))}`)
+    }
+  })
+
+  // 5. Check whether the Typst heading tokens exist at line 15-ish
+  const doc = view.state.doc
+  for (let ln = 1; ln <= Math.min(doc.lines, 20); ln++) {
+    const line = doc.line(ln)
+    if (line.text.trimStart().startsWith('=')) {
+      console.log(`\nLine ${ln} starts with '=': "${line.text}"`)
+      tree.iterate({
+        from: line.from,
+        to: line.to,
+        enter(node) {
+          const t = doc.sliceString(node.from, node.to)
+          console.log(`  node: ${node.name}  text: ${JSON.stringify(t.slice(0, 60))}`)
+        }
+      })
+    }
+  }
+}