Underbook

Underbook double-checks the hotel you are already looking at.

On a hotel page at Booking.com, Expedia or Hotels.com (and on many other booking sites and hotels' own websites), the Chrome extension looks up the same stay across booking sites and shows, right on the page, whether another site lists it for less. Prices are compared all-in where the sites report taxes and fees. Without the extension, the web checker on the Underbook site runs the same check for any hotel.

Honest by design: a lower price only helps if it is for the same room. When Underbook can match the room name, it says so. When it cannot, it shows the room and terms side by side so you decide. When the site you are on already has the lowest price, it tells you that instead of inventing a saving.

Why it matters: in three September 2026 snapshots of 424 to 434 hotels each (50 cities in all), 78%, 79% and 81% of hotels had at least one site listing the stay 5% or more below the going rate. Most of those cheaper listings did not name a matching room, which is why Underbook shows you the room before you switch. The study and its data are published on the Underbook site.

Optional price-drop alerts by email. Free to use: when you book through a link Underbook may earn a commission at no extra cost to you, and it never changes which prices are shown or their order.