Steam doesn't provide a way to check the integrity of all of your games at once. However, someone has made a script that you can try to run that verifies all of your games in one shot.
A link to the Reddit post can be found here. It gives an overview of what the script is. In order to run this script, you will need AutoIt. After downloading AutoIt, you can run the script. According to the post, you should be able to even see what the script is composed of as well.
The Reddit posts points out a few things to keep in mind:
- Your computer should not be actively in use when the script is running
- Steam windows showing the game that is being verified will still pop-up, but they should be automatically be closed upon completion. If you are using other programs with the tool running, it is possible it may close the wrong window
- You can skip specific games if you wish by adding the games SteamId to the "validationBlacklist.txt" file in this format:
15620 20570 220240 19900 50130 50620
There is also a link to a self-contained .exe version of the script, however the link for that one does not appear to want to work (at least for me). Note that you should also be cautious when downloading files like this off the internet, so take any chances at your own risk! Also be sure to follow the instructions listed in the Reddit post. It is a bit of a lengthy one to post all of it here.