If a company already has a public website, why can't another app just use that — why is a webservice needed?

A website outputs HTML meant for human eyes; a machine can't reliably extract the data from it, so providers expose a separate webservice that returns clean, structured data.

Imagine you're booking a Mallorca package — flight, hotel, bus tours — and want to compare prices across Swiss, a hotel chain, and a tour operator. The problem: each company only gives you its public web page. That page is built for a person: prices are buried inside layout, styling, and ads, and the markup changes whenever they redesign. Writing code to "read" that page (called screen scraping) is fragile and breaks constantly.

A webservice solves this by offering a second, machine-facing door to the same data. Instead of an HTML page you get a predictable response like JSON, with named fields you can read directly:

{ "from": "ZRH", "to": "PMI", "price": 129.00, "currency": "CHF" }

So the distinction is the audience: the website serves humans, the webservice serves other programs. That is the gap external webservices fill.

Tip: This is why webservices are described as "stable, exact interfaces" — unlike a web page, the response shape is a contract other systems can depend on.