Where is my train?
An estimated next stop, not a GPS position
The question has an honest answer, and it is narrower than you would hope.
What SNCF publishes
The data used by this site lists announced stops, reported times and reported cancellations. It does not confirm that a train left one station or reached the next.
It lets us estimate the next stop from available times. This estimate does not prove where the train is.
What this site cannot confirm
A position to the metre. It is not in the data used here. A dot drawn between two stations would be an interpolation: halfway along because half the time has passed, which assumes a constant speed nobody has measured.
It would be an invented value wearing the appearance of a measurement, and that is exactly the kind of number this site refuses to show.
Following a train
Every train has a page under its number. It lists the stations where the train is announced, in route order, with the available reported times and delays. Cancelled stops remain visible but do not advance the estimate. After the last served stop, “Run ended according to the timetable” does not mean that arrival has been confirmed.
The number is the one on your ticket and on the screens in the station. It is also the address of the page, which makes it shareable as it is.
How often
The page checks the data regularly and recalculates the estimate after a successful check, even if the times are unchanged. If the check fails, the last data stays visible and the indicator freezes with a warning. Returning to a hidden tab triggers a check before resuming. A successful check by the site does not by itself certify the health of the upstream source.
Why is the train's exact position missing?
The data used here provides neither a GPS position nor confirmed passages. The next stop is estimated from available times, not a measured position.
How often is the information updated?
The page checks the data regularly. Unchanged times do not mean a failure. If that check fails, the indicator freezes and says that updates are unavailable.
How do I follow a train by its number?
Open its page: the number is its address, and it lists the stations where the train is announced, in order of passage.