Every airline ticket carries a single-letter booking class (also called an RBD or fare class) — Y, B, M, Q, S, O and so on. Airlines operate a ladder of eight to twelve of these classes inside economy alone, and the letter decides what your ticket really is: whether changes are free or punishing, whether a refund exists at all, how many frequent-flyer miles you earn, and whether you're ever eligible for an upgrade.
Most travellers never see that letter. It hides in the fare basis code on your e-ticket, and a quote for “economy, Delhi to New York” can sit anywhere on the ladder. On multi-leg journeys, different legs can even be booked in different classes — an outbound in a mid-tier fare and a return quietly in the most restricted bucket — without the price telling you.
Ticket Fare Check reads the booking class off every leg of your ticket — any airline, any route — and translates it against the airline's own fare ladder, so you know exactly what you were sold — and what to ask your travel agent about next time.