Can a prompt replace Going?

Build a fare watcher for a small, fixed set of routes you would genuinely book.

Define watches in a config file: origin, destination, a date range or a flexible month, cabin, and the number of passengers. Keep the list short — this design is deliberately deep rather than broad, because breadth is the part that needs a commercial data licence.

Query a flight search API on a schedule. Free tiers are thin, so poll each route a few times a day at most and stagger them. Store every observation as a row with the price, the itinerary and the timestamp; never overwrite, because the history is what makes the alert meaningful.

The alert rule is statistical, not a fixed threshold. For each route compute the median and the interquartile range of the last ninety days of observations, and alert when a price falls below the median by more than a configured number of interquartile ranges. A fixed "under $400" rule fires constantly on cheap routes and never on expensive ones; a distributional rule adapts per route without any tuning from you.

Every alert email includes the price history chart for that route, so you can see whether it is genuinely unusual or merely the bottom of a normal weekly cycle. Rate-limit to at most one alert per route per week.

Add a suppression list for fares with characteristics you will not book — more than one stop, overnight layovers, basic economy fare classes — filtered before the alert rather than after.

Do not scrape airline or aggregator websites. They forbid it, they block it, and a scraper that half works produces alerts for fares that do not exist, which is worse than silence.