rate my itinerary

I spent about a month in Belgium this summer. It has a lot of attractive cities. But two nights is a very short time to allot to an entire country. If you haven't been to Paris before, I'd vote for adding the 2 nights to Paris.

If you dont have a need, using points or cost or schedule, flying into Frankfurt might be a better start.

I would first plan out London and Paris to some detail before considering Belgium. Depending on yout interests and if this is your first trip to Paris you could easily spend 6 days there with few or no day trips. Its the holiday season which for many is best spent at a slower pace.

If you come back you might get more input eit more detail. Where are you coming from, have you been before, actual travel dates and even age and of course interests and what you enjoy.

But looks like a fine trip to some wonderful holiday destinations.

You could visit the Black Forest, across the Rhine from Strasbourg.
Also, don't miss Brugges in Belgium.

I agree with acraven about adding 2 nights to Paris and removing Belgium (unless you have a very compelling reason for going there). Belgium is charming and I really enjoyed it, but with only two nights there, that leaves you just one day to see one place. To me, it wouldn't be worth spending the time and effort to get there by either train or plane and then have to travel on from there. It would be so much easier (and nicer, imo) to spend 6 nights in Paris, then take the Eurostar from Paris directly to London. You will save so much time and so much money, and have a really nice experience in Paris without rushing around to see everything.

You could visit the Black Forest, across the Rhine from Strasbourg.

I also agree with this. It's a very quick and easy day trip from Strasbourg to Gengenbach, Germany, which is a charming village in the Black Forest filled with half-timbered houses, quaint streets, and nice restaurants and cafes. It only takes about 40 minutes by train to get there, and it's a very walkable place, filled with lovely things to see and do.

ETA: I forgot to mention that Gengenbach also has a huge Advent calendar on their Town Hall that is one of the largest in the world, and it would definitely be worth seeing. You can find more information here: https://www.npr.org/2024/12/01/nx-s1-5208955/the-german-town-with-a-magical-advent-calendar-thats-as-big-as-a-town-hall

I heartily agree with the suggestion to also visit Germany from Strasbourg, whether as a day trip or overnight. I can definitely recommend Freiburg im Breisgau. Direct bus from Strasbourg, compact city with excellent Xmas market.

That sounds like a great trip for December. Strasbourg and Colmar will be perfect for Christmas markets, so four nights there makes sense. I’d keep Paris at four nights too, enough time to see main sights without rushing. If you’ve never been to Belgium, adding two nights is a good idea, maybe Brussels or Bruges for the festive feel.
It’s a nice balance of big cities and smaller Christmas towns, and your travel route is logical. I wouldn’t add more days in Paris unless you skip Belgium.

I just got back from Belgium and enjoyed it, but with only two days I'd probably skip it this time to add days somewhere else, or skip Paris and add to Belgium. We spent 5 days in Bruges which included a couple of day trips. For you day trip to Colmar, consider a tour that would take you to some of the towns in between. It's a beautiful region