And as you can read above, none of this is documented anywhere, especially not for a lay user.

"If you are unsure of the integrity of your files, here are some methods you may use".

https://www.gog.com/forum/general/any_md5_check_available/post4
1. Wrong. It was documented in this thread and others. However, the info is just a tad dated since the download links have slightly changed since then. The advice is still decent enough to get there if you dare anyway. Not difficult in the slightest.
2. Who cares if it's not for a lay user. Linux is not for the lay user either, and you promote the hell out of it frequently.

I hate the fact GOG didn't make all this painless and offer it freely and natively, but that's not the point of this thread at all - it's to teach others it's possible and how it's done.

It should be included . For example next to download links for offline files. Dont know why gog dont make it easier for users :/ Or maybe some textfile with alll md5 checksums , especialy for big games.

I agree, but no doubt they want us all to use Galaxy, which would likely do the MD5 checking on the Offline Installers, and of course individual files are checked during install, Galaxy or not.

Since GOG has not implemented this, it is up to others in the GOG community.

thank you 'xmanacollectorx'

https://www.gog.com/wishlist/site/my_account_provide_checksums_eg_md5_sha1_etc_for_downloadable_files

https://openuserjs.org/scripts/xmanacollectorx/GOG_Checksum_Lookup

Or if you are going to use a script anyway, you might as well use one of the already existing third party command-line apps, that have been using the GOG SDK/API for quite a while now.

gogcli.exe (Windows & Linux, and doesn't require Python to be installed)

gogrepo.py (Windows & Linux)

lgogdownloader (Linux)