Flight Search

This builds your search and opens it on the flight site, where you'll see live prices. Google Flights handles city names; Skyscanner works best with airport codes.

Stripping everything that is not a plain letter turned Malmö into "malm"

One of these buttons builds a URL out of the place names by lower-casing them and deleting anything outside a–z and 0–9. For "New York" that gives "newyork", which is what is wanted. An accented letter, though, is not outside a–z by a little — it is a different character entirely, and it goes with the accent.

9 of the 13 came out wrong, and every one of them had an accent in it. The link still opens and the search still runs — it just finds nothing, or finds somewhere else. Malmö lost its last letter outright.

The fix is to decompose first. An accented letter can be written as one character or as the plain letter plus a combining accent; converting to the second form and then deleting the accents leaves the letter behind. 4 plain-ASCII names come out byte-identical to before, and an accented spelling now agrees with its plain one — Zürich and Zurich reach the same place.

The 12-character cap survives the change and is generous enough for real names: San Francisco and Rio de Janeiro land exactly on it without losing anything.

And a return date before the departure built a URL anyway

Nothing checked that the two dates were in order, so picking a return before the departure produced a perfectly well-formed link with them the wrong way round. The site at the other end has no way to tell that from a deliberate request.

The backwards one is 260910/260903 — the right shape, six digits and six digits, which is exactly what made it invisible. It is caught before the link opens now, which is the only place it can be caught: once the URL is handed over, the mistake belongs to somebody else to interpret.

A same-day return is allowed, because it is a real thing to book. A one-way has no return to compare. And a trip across a year boundary passes, because the date format sorts as text — which is the small reason the check can be a string comparison rather than date arithmetic.