The question is really two-fold:

Is it possible to cheat a pagespeed analyzer by detecting the useragent (~Lighthouse | other pagespeed crawlers) and serving a reduced and faster version of the website? If yes, will this be detected over time and get you blacklisted?

Also, the opposite, is it possible to provide extra data (json-ld) to the crawler that you don't want to load for a normal user?

  • This is black hat SEO so, yes, you will be penalized.
    – John Conde
    Apr 3, 2019 at 10:38
  • Thank you, that sounds reasonable. Do you have a source that would elaborate on the topic?
    – Ferenc
    Apr 3, 2019 at 10:43
  • Google PageSpeed Insights is a tool for your benefit only - Google doesn't determine ranking from this tool's results (this isn't Googlebot). By cheating this tool, you are only cheating yourself. I don't see why you would be "penalized" for cheating this tool? Why would this be "black hat SEO"?
    – MrWhite
    Apr 3, 2019 at 20:03

2 Answers 2


You want to cheat a bot, which Google don't use it for ranking. Pagespeed insights/lighthouse etc are just for our own analysis purpose, Google don't use that bot at all to determine your web pagespeed. Google just come with their own bot name, Googlebot and crawl your content and major pagespeed.

And if you serve different content to Googlebot then it will term as cloaking. Bur normally if you block some javascript/ajax file which is just for web design purpose then it's totally fine, but do it via robots.txt file only.

I've seen some people block javascript file which download fonts online. Google don't recommended to do even such a thing, but if webmaster do it then there is no any penalty. Because whatever you've block via robots.txt, then it will notify you, in your search console to know what you've blocked it and how they see your content.


Google doesn't use those bots to determine page rankings

To optimize your site's rankings, focus on serving up high-quality content at the best speeds you can achieve.

If you serve different content to the Google bots you detect, they'll find out about it when they send differently named bots to document any differences in the way content is served. If Google suspects that you're trying to game their ranking system, expect to be penalized and/or blacklisted with few options for recourse. This can permanently scar your site's ability to successfully draw in traffic, even if everything thereafter remains in perfect accordance with their policies.

Your site's robots.txt file determines how to interact with Google's bots. Check out their guidance for this here: https://support.google.com/webmasters/answer/7424835?hl=en

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