Best way to find train routes if you can read Japanese
The app has train operators other than JR East too, so you can use it generally to navigate, not JR East only. There is a option for JR only though, maybe good for JR Pass or JR East 23ku pass.
The way the app presents route options is really good and reminds me of the old Google Schedule Explorer, but vertical. This is the best way to look at route options imho.
The language is Japanese only though, so you at least need to be able to understand basic Japanese and know place names. You can search the station names in romaji but the display is only Japanese.
Language Barriers
Sadly I can’t read Japanese and I did not find a way to translate the app to English, or German or Spanish or other languages. It would be very helpful if the developer would include multiple languages in the app.
This was so helpful when I visited Tokyo after 10 years of being away. The rail system has changed a lot since, with so many new lines and newly connected lines between different companies. The app shows you the easiest, fastest and/or cheapest routes to take. It also lets you know if there are delays due to accidents or mechanical malfunctions on the line.
I wish there were an English version of this. I didn’t see language options. Although you can enter station names in English, they only show up in kanji. If there are multiple stations for what you entered, you may have a hard time figuring out which one is the right one.