PageSpeed "NOT_HTML" error on Shopify store

54 6 13

Hi all,


I'm trying to use Google PageSpeed to optimize my speed on various pages. However, recently I'm getting an error when trying to do so as below:


"Lighthouse returned an error: NOT_HTML. The specified page is not HTML (displayed as MIME type text / plain)."


This seems to be related to a general issue on Shopify and I'm concerned whether this may indicate a more general overarching issue. Any thoughts on how to resolve this?




Accepted Solution (1)

Accepted Solutions
Shopify Partner
2 1 3

This is an accepted solution.

Hi all,


I received the following reply from Shopify support:


Thanks for reaching out with this concern with your Google Page Speed. I understand how important Google rankings can be for our merchants, so rest assured we'll get to the bottom of this.


Doing some digging on my end here I've located the source of this error: we've been working with Cloudflare and Google to enable a new feature on storefronts that will allow for faster page loading. It's called 103 Early Hint, and is very new, so Google is still working on adding support to Lighthouse.


You can keep an eye on this Google Lighthouse GitHub issue page for more info on when they're expecting this new feature to be supported. As of now they're saying it's a priority, but they have no ETA.

View solution in original post

Replies 17 (17)
4 0 2

Me too! Google speed test recently upgraded, I saw the changes on the 15th while testing. It might have something to do with that. 

What I do now is I copy the live theme, or the theme I look to improve on, and I use a preview link of that copy to test with google. I know it is not completely accurate but until this gets fixed either by google or by shopify we can still use it.

Let me know if you have another solution to this. Thanks!

Shopify Partner
90 30 25

We have clients experiencing the same issue. Older implementations of lighthouse work fine, but the one used by the upgraded PageSpeed Insights auditor is returning a NOT_HTML error. 


Perhaps a server configuration issue on Shopify's end, conflicting with a new version of lighthouse?

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24 1 4

My store as well. Hadn't thought of running the preview link to get page speed info. Thanks for the temporary fix.

New Member
1 0 0

I'm experiencing the same issue on all of our shopify sites. I imagine this is something shopify will need to update. 

New Member
3 0 0

Relatei ontem pelo twitter ao shopify o mesmo problema e me deram a resposta final que seus desenvolvedores vão atrás da solução para o problema. Obrigado a todos que relatam pelo fórum, pois só assim um problema tão grave quanto este poderá ser solucionado agora muito mais rápido! Pakinha Adesivos do Brasil.

3 0 1

Happening on my end as well

New Member
3 0 0

I'm having the same issue after moving to an update of our theme that supports OS2.0, but rolling back to the previous version does not fix the Pagespeed Insights Error

New Member
2 0 0

I have not even switched to 2.0 but I ma still facing the issue n

Shopify Partner
2 1 3

The same issue is happening on every Shopify site that I develop/manage, including my own shop. My Shopify site speed number plummeted 16 points since the change to Google PageSpeed Insights and our site rankings are taking a hit. Hope a fix is in the works.