Money and trust

When you open a booking site through Underbook and book there, Underbook may earn a commission from that site, at no extra cost to you, and it never changes which prices Underbook shows or their order.

Underbook is free, with no paid tier, and never takes payment from you or sells your data. A click on a booking-site link passes through Underbook's service, which adds one to a daily click total, turns the link into a partner link where the site has one, and sends you on; it does not record who clicked. The listings are sorted by price before any link is made, and a lower price is shown even when its site pays Underbook nothing. In the newest version (from 0.5.33) every result with booking links says so in its fine print. More: how we make money.

Underbook asks only for the access it needs to find a hotel page and show prices on it, never books anything, never sees your payment details and loads no code from outside its own package.

• Access to the sites you visit, so it can appear on any hotel page. On other pages it sends nothing about the page.
• activeTab and scripting, so a click on its icon can check the page you are on.
• Storage, for its settings on your device and, if you set a watch, your email.
• A connection to Underbook's own price service, underbook-backend.underbook.workers.dev, where the comparison runs.

It is published on the Chrome Web Store, Microsoft Edge Add-ons and Firefox Add-ons. You always book on the booking site you choose. Mistakes we have found in what we publish are listed in our corrections log, and the privacy policy says what each permission is for.

Usually, if the offer is still available: in our click-through test of September 30, 2026, 7 of the 10 pages we could read showed our price, a lower one or one at most 5% higher, but offers also disappear, so check the final total before you book.

What did not last was the offers themselves: at 6 of 10 hotels where Agoda had listed the lowest price, its offer was gone from Google Hotels or sold out within 2 to 3 hours. Some lower prices also come with conditions: KAYAK's lower price was KAYAK's own rate, bookable only with KAYAK, and two of three Vio.com prices said "Sign in to book". The test was small (1 to 5 offers per site) and opened no checkout page. Details: what we checked about our own accuracy.