Haven't been able to confirm the dress code for men at La Giostra in Florence.

Is a coat/tie necessary? If so, it this for dinner only?

Thanks.

http://www.florence.ala.it/giostra/ will show you one rather casual atmosphere. http://www.ristorantelagiostra.com shows a slightly more 'dressed' atmosphere, in my opinion without being really 'formal'. The men have hung their jackets on the back of their chairs.
A tie will certainly be appreciated, but from the pictures I shouldn't say it is an absolute necessity.

Wear a jacket, skip the tie. A white button down shirt and jacket are (almost) always elegant enough for most restaurants.

My dear Melissa, button down shirts are the most casual collars available. They never look smart, always a mess. No designer (we're not talking Polo by Ralph Lauren here) features button down shirts in their collections. Wear a jacket, and if you are slim, a T-shirt in a plain colour by Prada (mainline), Jil Sander, Gucci.... i.e. one which is of a fine material, and for the evening a darker colour - certainly not white. If you feel more comfortable in a shirt, then any, what you Americans call "dress shirts" (although I take dress to mean evening wear) without a button down collar will do. A word of caution, if you do not wear a tie, a Cut-away or even mid-cut-away collar will look odd, therefore these are best avoided.

Furthermore, a coat is an outer-garment, so a "coat and tie" refer to an overcoat and a shirt with a tie, even worse!

A jacket is a jacket and a coat is a coat, please note the distinction.

Ties are rarely required for dinner, let alone lunch. The Italians (we're talking under 50s) are masters of the Italian collar, i.e. one worn without a tie.

We ate there last year (wonderful!) and another alternative that was seen would be a nice light sweater with a collared shirt underneath with nice slacks. The men's tops were less regimented than the bottoms. No Jeans! Nice dark slacks will do. I suppose it hasn't changed much and frankly, this restaurant is well-known for its hospitality so I don't think you would be made to feel out of place whatever you wore.

This is partially off-subject but I must disagree with m_kingdom2's sartorial advice. Italians have had a strange fascination with Brooks Brothers button-downs for decades now - so much so that the company is actually opening some stores in Milan. If I recall correctly, a few members of the Italian fashion elite used to love wearing them unbuttoned - the loose collars must have flopped elegantly, or something. I admit it is beyond me, but even in more conservative Florence no one would look askance at a button-down collar. The Italians are masters of breaking the rules of fashion with panache.

Button down collars, however, do not feature in any contemporary Italian designers' collections. In the more classic collections, they feature as a button under so the buttons are all but invisible to the casual observer.

To get back to your question: I was there with a fairly large group for dinner. I'm sure none of the men in our group wore ties and I don't think all of us wore jackets. It is not an extremely formal place.
By the way, we really enjoyed dining there.

Just returned home last night. No tie or jacket necessary. Excellent restaurant, probably my favorite.