Tokyo Station transfer time Yamagata-Tokaido

Hi guys, do you think 12min is enough for transfer from Yamagata Shinkansen to Tokaido Line at Tokyo Station? I want to reserve a Yamagata Shinkansen ticket from Shijo to Tokyo (arrive at 12:48, maybe platform 22) and have to catch the Tokaido JR line (depart at 13:00, maybe platform 9). Do you think 12min is okay for me to catch the Tokaido train?
Many thanks!

I would say no, but then again I have a history of getting lost in Tokyo station. If you can check the route using streetview and are not encumbered by large luggage it should be quite possible.

Hi!

I could do it? It really depends on how much stuff you have and how well you navigate in general. I personally find Tokyo Station easy to navigate, though I am not overly fond of the transfer to the Keiyo line because it's so far from everything else. I am pretty sure that the Tokkaido line track is one of the first tracks once you exit the shinkansen line to the other JR lines.

http://www.jreast.co.jp/e/stations/e1039.html

Just make sure you exit towards the JR line transfer/Central Marounouchi exit. Don't head towards any exit that says Yaesu. If you are going to Yamagata from Tokyo spend a few minutes walking around inside Tokyo Station first so you know where you are going.

Good luck!

No problem, it should be enough for 5 to 7 mins.
http://www.jreast.co.jp/e/stations/e1039.html
https://postimg.cc/xcV7Z9PT

Yamagata Shinkansen "Tsubasa 136" enters the Tokyo stn from map left (= North).
Walk to front car side, then down to lower floor.
Pass through the transfer ticket gate where is for entering conventional lines area.
A bit walk and find display of line 9, then go up to the upper floor.
Next train "Super View Odoriko" goes to map right (= South).

(note)
SV-Odoriko has no non-reserved seat cars, so you can NOT take without reserved seat ticket.
There is no time to make a reservation at Tokyo stn
and even if you try to buy it at Shinjo stn on that day, however, it may already be sold out.
But you can also buy it the day before if not sold out, please check in nearest JR stn ASAP.
Online reservation is also possible even if from out of Japan, but I do not know you can do it or not.
http://www.jreast.co.jp/e/ticket/reservation.html

Regular "Odoriko(by 185 series)" has non-reserved seat cars.
http://www.jreast.co.jp/train/express/odoriko.html
https://en.wikipedia.org/wiki/Odoriko

If you have a reserved train to catch at Tokyo, then you would have reserved seats for both the shinkansen and the following train. 12 minutes is lots, and you are only going half-way across the station and not any far flung connections. If you are just getting an ordinary local train, then the 13:00 is possible less of an issue - and there are lots of trains anyway.
However, I suspect you are getting the 13:00 SV Odoriko as mentioned above - what is your actual final destination? If it was Atami, then the shinkansen is an option.