Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/routes/sheet-builder-app.tsx

@@ -0,0 +1,17 @@
+import { useParams } from "react-router-dom";
+
+import useUserName from "~/hooks/useUserName";
+import { SheetBuilderApp } from "~/tools/js";
+
+export default function Builder() {
+  const { characterId } = useParams();
+  const username = useUserName();
+  let parsedId: number | null = null;
+  try {
+    if (characterId) {
+      parsedId = parseInt(characterId, 10);
+    }
+  } catch (e) {}
+
+  return <SheetBuilderApp characterId={parsedId} readOnly={!username} />;
+}