Google Flights (free) is one of the best sources for a second opinion you can find on the Web. Google Flights is a small slice of the Google search universe that only looks at airline travel, and, since the site first appeared more than a year ago, it has corrected some of its major limitations. You can now search for roundtrip flights to cities around the world, as well as one-way tickets and multi-city trips with up to five legs. The site still doesn't let you book a ticket directly through Google—you have to link out to another site—but it does include a lovely array of tools for narrowing down your travel criteria and looking at alternative options.

In the end, though, Google Flights works best as a free second opinion to Kayak (5 stars), our Editors' Choice for travel search and booking. Kayak offers everything Google Flights does, and a whole lot more. But Google Flights has a slightly smoother interface, so wading through certain kinds of search results. Still, it's one of the 15 best travel apps and services you'll find.

Why Use Google Flights?

The primary reason to use Google Flights, despite its lacking some features we consider basic in travel websites, such as the ability to add hotels and car rentals to an itinerary, is because it's fast. Wicked fast.

When you land on the page, you can start typing the name of any city, and Google Flights will suggest ones you probably mean. Below those entries are date fields for arrival and departure. A third row of additional filters, including the number of stops you're willing to make on the way and a slider bar to limit the price, work equally fast as the primary search.

By default, Google Flights starts on a roundtrip search, but you can change it to a one-way or multi-city flight by switching tabs at the top. With the all the changes you might make to a search, Google Flights never has to fully reload the page, which is astoundingly different from the experience of using Kayak, Orbitz, and any other major travel search and booking site.

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You can also turn on a map that shows you the most direct flight line between the two locations. New York to Honolulu looks a lot farther than it sounds.

A second visual indicator, and my favorite tool on the site, is a bar graph icon indicating an interactive graph that shows how the price changes if you opt to travel on different dates. Kayak offers a similar tool, but you have to delve pretty deeply into that site before it turns up. On Google Flights, you can adjust the number of days of the trip while using the flexible date option as well. For example, a roundtrip flight between New York and Honolulu December 26 to January 4 hits a peak price of more than $1,500, but the bar graph shows that a much better fare of $652 can be had if you just slide your dates of travel over to December 31 to January 9. That's less than half the cost, so you can see how worthwhile it might be to have flexible travel dates. For finding the best time to fly based on price, Google Flights is awesome.

There are more criteria filters to try, such as changing the class of the airfare (economy is the default), or limiting the airlines which Google Flights will search.

Google Flights doesn't let you buy the flight right on the site, making it only useful for travel search rather than booking. You have to link out to another site, usually that of the airline carrier, to make a purchase. Google Flights doesn't include hotels, car rentals, vacation packages, which you'll find in Orbitz and Kayak, either. And, seeing as you can't buy on the site, Google Flights doesn't offer any customer service or price guarantees along the lines of what Orbitz offers.

Check With Google, Book On Kayak

Kayak still leads the pack for travel search and booking sites, and it's our Editors' Choice. If you have a lot of factors to take into consideration for your travel plans, start with Kayak and run a quick cross-check on Google Flights, which is so fast it will only take you a moment to drill down your options and find exactly what you need.