This website allows you to search for the formation of rail services in Switzerland. Simply enter the train operator and number to see the expected vehicle formation.

There are a few limitations:

• You can only search for services departing today or up to two days in the future (although I have yet to find a formation loaded that far in advance)
• Not all services/operators are available - notably formations do not always appear for non-Swiss vehicles or for services that start/terminate in a different country
• Vehicle number searching only works for services that have been searched already (although I cache as many as possible during the maintenance window)
• The system allows 50 queries per minute, so I cache the searches but you may still be rate limited

Despite these limitations, I hope this site proves useful for helping you know what to expect on a given service. All data comes from opentransportdata.swiss and I am not responsible for any inaccuracies in the data they provide. I'm also not an actual web developer so this site may break at any time!