The nerds in MailChimp Labs just unveiled a new experiment called the Subject Line Suggester. It’s kind of like Google’s Keyword Tool, but for email marketing. It’s a free feature for all MailChimp users.

You basically enter some words or phrases that you were planning to use in your subject line, then MailChimp will compare it to all subject lines ever used in our system, their resulting open rates, and then tell you how they performed.

For example, let’s say you want to send a holiday campaign, with the subject line “Holiday Gift Ideas:”

When you create a campaign, look for this link!

Hmm, maybe you’d like MailChimp to suggest other words or phrases…

Click the “research” link:

and on the next screen, enter some of your words:

Notice I didn’t enter the exact phrase. I only entered “holiday gift” to keep it a little broad. Hit “search” and wait.

MailChimp will then tell you how those words have performed in the past. As you can see from the screenshot, you might want to check out “Holiday Gift Guide” instead, because it performed better. Or, maybe you should consider using our patent-pending A/B testing tool to experiment with both subject lines.

Notice we don’t give you exact numbers on open rates. We give you nice, pretty little stars. We’re not going to open a can of worms by promising that the word “Free” will give you +40% open rates. The idea here is to simply give you more — well, ideas.

Now keep in mind, this is only our first stab at predictive reporting. It took months to generate this data, using our in-house supercomputer, some genetic pairing science, and Amazon EC2. Actually, we were doing something else entirely with our experiment, but this happened to be a cool byproduct, so we added it to our app.

Point is, we’re far from complete, and it’s far from perfect, but this’ll get better as more people use it and send us feedback.

Be sure to check out some of our other experiments over in MailChimp Labs