Answer: First, try Little Warden, a solid tool that monitors your pages and much more. It’s not free, but it's probably worth it when you think about the potential financial hit from unintentional noindex tags.
If budget is an issue, consider BetterStack. You can set up free monitors to look for specific strings in the response. For example, you can create a monitor that alerts you if a noindex tag shows up in the HTML. Even if your site is JavaScript-heavy (e.g. Next.js), this approach works if the tag ends up in the rendered HTML.
