Not really. At least, not in a way that doesn’t require constantly updating the website.

“Soups of the day” are generally an outlet for leftovers or a way to use up less desirable parts of other produce without just tossing them, so generally they’ll make whatever they have with what they got.

In theory, sure,

In reality, I promise you no overworked restaurant staff wants to bother with updating a website daily on the off-chance someone needs to know the soupe du jour. You'd probably just get the wrong information because no one updated it.

If you absolutely must know the soup availability, you can always just call the restaurant. The employees will make fun of you behind your back, but they'll pretend to be glad to inform you!

Yeah I kinda wonder because I see it often enough on online menus. it will say X, and Y, and such and then soup of the day and yeah you have to go to find out what it is. Generally I have a soup in their everyday that im fine with. It sorta cracks me up the everyday soups sometimes. Like one place always had matza ball. I figure if I had one it would be tomato that is vegan friendly and then chicken noodle and like a beef and vegetable.