Free Chrome extension
Underbook sits on the hotel page you are already looking at, checks roughly 12 booking sites for those exact dates, and shows you the result inline with taxes and fees included. No retyping your search into another comparison site. The unusual part: when every site is charging the same, it tells you that too, rather than inventing a saving.
Free, no account needed to compare. You always book wherever you choose.
Open a hotel on a booking site as you normally would. The extension reads the property and the dates already on screen, then asks what the other sites are charging for that same stay. A single banner appears with the answer. There is no separate tab, no second search to retype, and no form to fill in.
Around 12 sources
Mainstream booking sites alongside the discount resellers that usually hold the lowest listed number.
All-in, not headline
Compared with taxes and fees included where the source reports them, because the nightly rate on the page is often not what you pay at checkout.
Flagged, not hidden
If the cheaper listing does not name the room it is selling, the banner says so instead of presenting it as a like-for-like win.
Most comparison tools show you the wins and quietly skip the rest. Here is the full distribution from 618 comparisons we ran across a test basket of hotels, which is the same data we use to decide what the banner is allowed to claim.
| What the comparison found | Share | What it means for you |
|---|---|---|
| A lower rate, room not confirmed | 52% | Something is cheaper, but the listing does not say which room. Worth opening, worth checking before you pay. |
| Everyone charges the same | 28% | Genuine parity. You already have the rate. Stop shopping and book. |
| Confirmed cheaper on a named room | 9% | The clean win. Rarer than the marketing in this category implies. |
| Could not price it | 12% | Small or unusual properties we cannot match reliably. We say so rather than guess. |
Read that second row again, because it is the one nobody advertises. Roughly a quarter of the time the honest answer is that there is no saving to find, and a tool that never tells you this is not saving you money, it is just spending your time.
On a typical comparison, the mainstream booking sites cluster tightly at one price and publish exactly which room they are selling. The sites well below them are usually reselling wholesale inventory, and they frequently publish no room name and no cancellation terms at all.
So a large apparent discount is often not the same product. It can be a smaller room, a non-refundable rate, or a booking the hotel has no record of until you arrive. That is not a reason to never use those sites. It is a reason to know which kind of number you are looking at before you click.
This is the entire reason the banner distinguishes between a confirmed cheaper room and an unconfirmed lower listing. Collapsing those two into one cheerful "you saved" message would be the easy thing to build, and it would be dishonest.
Metasearch sites like trivago, Kayak and Google Hotels do compare prices, and they do it well. The difference is where the comparison happens. They require you to leave what you are doing and search again in their interface, which is also an interface with commercial ranking in it.
An extension inverts that. The comparison comes to the page you already chose, for the dates you already picked, and then gets out of the way. There is no ranked list to scroll and no sponsored row at the top.
The tradeoff is honest to state: a metasearch site can show you hotels you have not thought of, and an extension cannot. It only answers one question, which is whether the hotel in front of you is priced well.
Comparison only helps before you pay. After that, the useful move is watching. If you booked a refundable rate, a later price drop is money you can still recover by rebooking at the lower rate and cancelling the old reservation.
Underbook can watch a stay and email you if the all-in price falls. That part needs an email address and nothing else, and it works without installing the extension at all.
Watch a hotel price — freeIt works on mainstream hotel booking pages where the property and dates can be read from the page. It deliberately does nothing on search result pages, on sites where it cannot identify a single property with confidence, and on short-term rental listings, which are not hotel inventory and cannot be priced against hotel sources.
The hotel name and dates on the page are sent to our own service to run the comparison. There is no account, and comparing requires no email address. If you choose to watch a price, that email is used for that alert and nothing else.
Some booking links can carry an affiliate parameter, which is the normal arrangement in this category. It does not change which source is shown as cheapest, because the ranking is purely the price the source reports. The result you see would be identical either way.
The comparison runs after the page loads and renders as a single banner. It does not modify the booking site's own content or interfere with the checkout you are using.
Comparing and tracking are two different jobs and it is worth being clear about which you need. Comparing answers "is this price good right now" and happens in one shot on the page. Tracking answers "did it get cheaper since I booked" and has to keep watching for days or weeks. Underbook does both, but the tracking runs on our side and emails you, rather than requiring the browser to stay open. That means a price drop still reaches you on a day you never opened Chrome.
Yes. There is no paid tier, no trial and no account. If that changes, it will be said plainly here rather than discovered at a paywall.
Underbook compares roughly 12 booking sites on the hotel you are already viewing, taxes included, and tells you plainly when there is nothing cheaper to find. Free, no account, and you always book where you choose.
Add to Chrome — free