There is a user script that shows the hashes right below the download links.
https://openuserjs.org/scripts/xmanacollectorx/GOG_Checksum_Lookup

I am attempting to list the different download and verify options:
https://www.gog.com/forum/general/download_and_verify_options

Each to their own, but many of us have many games we haven't played yet, sometimes hundreds if not thousands.
For some of us it is about grabbing a game at a good price while you can, and also the DRM-Free aspect, which might disappear in the future.

And worth to me, while also being about how good the game is, is about having spent money on it too.
Especially as any experienced person who has been around long enough knows, your view of a game can change over time. So if I have bothered to spend money on a game or even just bothering to download it, I am going to bother backing it up, and that also means I am doing my bit for game preservation, because game preservation is ultimately about customers archiving.

Pretty pointless and potentially misleading to create a checksum value for files when you don't know if they are corrupt or not. Sure you can play the odds, but why then bother with checksum values at all.

And even playing a game is no guarantee that there isn't corruption somewhere in the files. Sure, if you install the game from an Offline Installer, and that process doesn't report an error, then yes it would be worth creating a checksum value for the Offline Installer(s). The install process gets the checksum value of every file in an EXE or BIN file package, and compares it to a list in the EXE.


Would you care to explain in greater detail, as I am totally ignorant of such?

Good On Ya!

You've missed one of mine, understandably, because I haven't really promoted it much yet (no separate thread).

MD5gog Bank - https://www.gog.com/forum/general/gogcli_gui_frontend_downloader_and_validator/post185

That said, it relies heavily on user input and sharing.

I was hoping to get enough interest, to pursue things further, because ultimately it relies on lots of MD5 contributions, from those who already have official checksum values.

Very interesting, and I just installed it.

No checksums showed up, until I happened to scroll up and saw there was a 'Checksums?' option I needed to enable in the game files popup window. That option being to the right of the 'More' dropdown option, in the OS and Language line.

I am running the JS script via ViolentMonkey.

For some reason, the checksum value doesn't appear for the EXE file (first entry), only the related BIN files, and some patches. And of course Extras don't tend to have an MD5 value in the GOG SDK.

But other than that 1 issue, it appears to work well.

An excellent little script. Would be nice to see GOG adopt it for everyone.

EDIT
Actually it wasn't an issue when I reopened that popup, though we need to enable that 'Checksum?' option every time we want to see the checksum values for a game, as it doesn't get remembered or set for all games.

I may be misinterpreting it, but the original post says "file integrity after the backup", not "after the download", i.e. wanting to be sure that the data you read from the backup is the same as you wrote to the backup.

I would suggest that if you have that many games that you haven't played, then corruption isn't your biggest problem. You're hoarding, and will likely never play a lot of those games.

It goes further than that. Even validating checksums isn't enough to ensure that a game is in a fit state to back up. I don't back up anything until I have played it because there have been too many instances of games being broken even when they aren't corrupt. Skyrim is a prime example of that, where there have been multiple patches over the years that completely broke it. Also a lot of games are broken when they are first released, so backing up the first version you downloaded would be pointless.

If you are going to play every game right after you buy them, why would you need to back them up anyway? You just buy them, install them, play them, uninstall them, forget about them, next game...

Of course, if you always wait until you are 100% sure you will play the game right there and then, before you will actually buy it:

1. Occasionally games get removed from the store. Too bad for you if you missed it because you waited for the urge to play it instantly. For instance, I am happy I bought the original Soul Reaver long before I actually played it as it got removed from the store in the meantime, and now some other people are miffed because they can't buy the original Soul Reaver anymore.

Similarly, I wish I had bought some of the Codemasters' racing games when they were still available here. Missed them. (It may be they were actually removed from the store before I joined here...)

2. It becomes quite hard to take advantage of e.g. sales and deep discounts, if you don't allow yourself to buy any game beforehand, before you get an actual urge to play them.

You are talking about quality control and game testing.

People get paid for doing that, you know? It shouldn't be your or our duty to playtest every game, to make sure the game is playable. It is the developers' and game testers' job.

Most games that are worth playing are worth playing more than once. Of course the question then is why not just download them again when I want to play them again? Firstly because of what I mentioned earlier about later versions of games sometimes becoming broken, secondly because it's quicker, thirdly because at some point in the far future GOG will cease to exist, and fourthly because I'm a bit of a hoarder (just a little bit).

Having said that, when replaying games I usually end up downloading them again anyway because they've usually been patched since I last played, and I may as well play the newest version (and replace the backed up version if it's working).

We only have the games as they actually exist, not as we would like them to be.

You are entitled to your view of course, but don't presume for me.
I am a big believer in variety and choice, and that just because I have something, doesn't mean I need to play or use it.
You think it a burden, me I feel rich ... like a King with treasure. I would be someone who just scrapes into low middle class, so not really financially well off, so I try to make the most of it, while the Sun still shines and an opportunity is there. From my perspective, I spend my money wisely ... and don't waste it on booze, etc.
And not only do I have lots of choice, but I have control of it.

Well, you accuse me of hoarding, so I am going to accuse you of being too pedantic, too cautious.

A successful life is always about some level of risk. Sometimes you just have to take your chances and hope for the best, and not get bogged down dotting all the i's and crossing all the t's. The most important thing in life is to live it.

Because of the offline installers sizes, depending on game, I've always tried to extract them using InnoExtract, play them, then 7z'p with maximum compression the game folder.

On some games, this works nicely.
On others, though, which require further steps that occur during installation, not so much.

The ones that this process works, because I've actually played them before backing them up, "there's no risk of offline installers corruption", as I've created my own offline installers.

Thing is, not everyone has the patience to do this.
That's why installers being divided by 4gb chunks still a thing too, which is a nice solution for this problem.
Albeit I'd prefer them to be 2gb chunks, if the argument were to help people with low internet speeds.

What we actually need, urgently, is Galaxy <> Offline Installers parity, above all else.
It's simply absurd that, if I don't want to use Galaxy, I must use alternative ways to download updated versions of games that are only available through Galaxy.

One idea I came up with the other day and shared here could solve those problems... well.. I guess.