I will travel Amsterdam for 5days next month. so I have some few questions.
When I go to a restaurant, Do I need to wear a suit?
and How about living as vegan in The netherlands?
I wanna try traditional dutch food, but Im vegan oriented pesco. I want to live as vegan as I can. So is there vegan food of dutch?

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You don't need to wear a suit for most places. You can live just fine as a vegan person here, there's lots of vegan food options in the supermarkets here and if you search on Google I'm sure you'll find vegan restaurants too.

Especially in Amsterdam they have a lot of vegan options in restaurants, even some restaurants which are completely vegan! And yes, no need to wear a suit. :)

I believe that in Amsterdam, there is a vegan junkfood bar.
It's pretty good

Yes, you'll be fine! And you don't need to wear a suit ~

There are indeed lots of vegan options in most restaurants in Amsterdam and also a couple of vegan restaurants like The Meatless District (it's a really good place) and the Vegan Junk Food Bar. If however you are somewhere in a restaurant and you are not sure if a meal on the menu is vegan, feel free to ask the waiter about it. I do it all the time (and I live in Amsterdam), it's perfectly normal to do :) There are also lots of grocery stores where they sell vegan products (I really like the Eko Plaza but you can also try Marqt). Have fun in Amsterdam!