For intrepid deal hunters, there’s nothing better than finding the perfect coupon code right before you click “Buy.” But finding valid coupon codes for online retailers usually requires a bit of click-work, and plenty of trial and error.

Enter Coupons at Checkout, a free browser extension from the folks at the deal site CouponFollow, that makes finding and testing coupon codes dead simple.

Once installed, the extension uses a patented process to find coupon codes when you reach the checkout page at more than 100,000 online retailers. Simply click the appropriate coupon code section of the checkout page and choose from a dropdown of known codes. The extension gives you an idea of how valid a coupon may be, and if it fails you can give feedback to warn other users.

coupons at checkout codesCoupons at Checkout supports Chrome, Firefox, Safari, and Internet Explorer. And unlike those dreaded shopping toolbars, the extension is invisible until you reach an online checkout page. The company says it may occasionally launch a browser tab when you click a coupon to track usage, and it will occasionally ask for feedback.

According to its privacy policy, Coupons at Checkout analyzes and collects your browser behavior around e-commerce pages, but no identifiable information is collected. Unlike many other companies, CouponFollow is at least clear what it’s doing with your data.

Marc Mezzacca, the New York City-based creator of CouponFollow, tells me that the extension’s users saved $22.45 on average (10 percent more than just manually fishing for coupon codes),  and it takes only around 21.1 seconds to find a working code, versus 80.7 seconds manually. So far Coupons at Checkout has been downloaded more than 12,000 times.

I’ve been testing out the extension while Christmas shopping, and so far it’s saved me a decent chunk of change. While there aren’t always working coupon codes at every retailer, at least with this extension you’ll know before wasting time searching the web.

Mezzacca notes that it’s not only helpful for consumers, the extension also benefits retailers: 87 percent of surveyed users said they would be more likely to complete a purchase if they saw a coupon when they were checking out. Currently, 27 percent of customers abandon their carts to seek out coupons, and only a third of those actually return, according to a recent PayPal study. Discounts also lead consumers to become an online fan of specific brands, and they also lead consumers to reconsider purchasing unbought items.

Next up for the extension: Mezzacca wants to improve the algorithms behind validating coupons, as well as track working coupons and their expiration dates better.

Photo via sdc2027/Flickr