Semrush issue - uncompressed JavaScript and CSS files

Morning - one of our clients uses Semrush for their Prismic site, this morning we've been alerted to a warning that could affect the site performance: 95 issues with uncompressed JavaScript and CSS files This issue is triggered if compression is not enabled in the HTTP response.

The URL that is flagged is

The suggested solution is:

Enable compression for your JavaScript and CSS files on your server.
If your webpage uses uncompressed CSS and JS files that are hosted on an external site, contact the website owner and ask them to enable compression on their server.
If this issue doesn't affect your page load time, simply ignore it.

Any suggestions?

Hi there,

Thanks for reaching out.

As far as I understand, the issue doesn't only concern Semrush (That I don't know much about) as it also applies to every website that uses the perview.js script.

And for that, I have reached out to our dev team to get some more info to know if it is possible to activate the compression or that needs to implemented.

I will let you know once I get any updates,

Hey Team,

You can check the link here, it's already compressed/gzipped:


Thanks Phil. I flagged this with Semrush who have advised:

The thing is that the pages that contain JavaScript are compressed, but the file itself is not. Please refer to the curl attached:

Hi @thejuniperstudio
I've got some feedback from our dev team

as of this test:

curl '' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Firefox/102.0' -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8' -H 'Accept-Language: en-US,fr;q=0.8,fr-FR;q=0.5,en;q=0.3' -H 'Accept-Encoding: gzip, deflate, br' -H 'Connection: keep-alive' -H 'Cookie: __stripe_mid=ec4c4355-43d5-4ad0-a34f-7e9c6e51e83aadeac5; intercom-id-bnnh3u9v=85f33841-d35f-4dfa-ba64-64be8886f785; intercom-session-bnnh3u9v=MWRJL25uaDR5bktxSFVFUGJoOHo1elMyNFNOSllGQ0NveGVvOFBaVngvWVg0S3NPU2xiSEpZNDBzNnNuZ0NxMi0tbFBBVWV0RHFkaDBlenhvSkdqcmtLQT09--18956bf2655619bd8305904a0b63e7211b902859; SESSION=58a8f38a1363555d8b00e36d819af9754a803535-T=ABQVJMI%27E%25%2FS%3C%3CS%26%2F%3A%3DP6B%40.L%22%26T+1%5E%3F%2B%3C6%292VX%22Y4M4%3CV2%2FUG_%26%28T89-0L%21%3CDGSI&; is-logged-in=1; X_XSRF=3e748fc1d37229f2e8c3860092e95fce4d8a000b720ddd520fa86e6cec9aa0d7-1652108093828-3a373398c8709a918af95dae4c7c4f5a8920211670f907bcc3bc45af8bd5d82877; prismic-auth=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ0eXBlIjoidXNlciIsImlkIjoiNTE3NjUzNDNhOWNhNGJjMGIyZDlkNTZkIiwiZGF0ZSI6MTY1MjEwODA5MywiaWF0IjoxNjUyMTA4MDkzfQ.Y4E3I3F3HZ0G5Gn5imnzwuTZfJN-rUmBzQb213Sekgk' -H 'Upgrade-Insecure-Requests: 1' -H 'Sec-Fetch-Dest: document' -H 'Sec-Fetch-Mode: navigate' -H 'Sec-Fetch-Site: cross-site' -H 'TE: trailers' --out /tmp/out

If you look at the out file, you can see binary data

It seems that the problem here is only that the response header content-encoding:gzip is missing, but the content is compressed, as shown in the curl request I've mentioned in the previous thread.

As shown in this screenshot:

And for that, I will create an issue in our tracker to have somebody from our dev team to investigate.

Please let me know if you need any further assistance,