Paris restaurants

Dame Tartine. Comptoir Gourmet.

Check out the videos on YouTube of "Les Frenchies" They have playlists of street food, best food, fine dining, where to eat, etc.

It's not in the Marais but I had wonderful salmon in March at La Chaumiere on Ile St Louis.
It was so good I had it again a few weeks later.
And my friends loved the mussels there.
Have a wonderful time in Paris!

This is one of my favorite topics. When my daughter saw that I was answering this she said "oh no, don't get her started" so I will be mindful and offer up 10 places, 9 of which I have eaten at and one on my list to try the next time I am in Paris.
https://www.lange20.com/en/
https://www.amarante.paris/
http://letempsdescerises-restaurant.fr/
https://www.lepetitmarche.eu/
http://aubourguignondumarais.fr/
https://www.chez-margot.fr/
http://www.les-enfants-perdus.com/ (not Le Marais but great for a Sunday brunch type meal)
https://holybellycafe.com/ (also not Le Marais but IMO one of the best breakfasts in Paris)
https://www.davidlebovitz.com/a-la-biche-au-bois/ (also not Le Marais but one of the best old school traditional French places in Paris)
https://brasserierosie.com/ (not Le Marais and I have not been here yet)

I love your lists JHK, thanks.
Holy Belly looks gooood.

On Rue Rambuteau, Le P'tit Mousse is a lovely seafood restaurant. It is not cheap, but I would say it is good value nonetheless, despite the prime location. It is small: reservations are probably wise.
For something vegetarian, Bonnard on Rue des Gravilliers is really great (again, best to book, but easy to do so online).

I'm so grateful to all of you who answered - thank you! I'll check these out and look forward to some great meals. We leave Monday - very excited!

Dorothy, we would all love it if you report back on your experiences.
And have a wonderful time.