Supposedly, what the National Security Agency collects from emails is metadata, not their contents.

The contents would be what you typed in — the body of the message, along with the subject line. Most of us would consider that the important part. But metadata reveals a lot about us, too: whom we communicate with, when, how often, and from which computers.

Because we often copy multiple people on emails, this data can also show relationships between people. We also sometimes label conversations or place them in certain folders to organize them, and that’s useful metadata, too.

To get a sense of what kind of picture your email metadata presents, Gmail users can check out MIT’s Immersion Lab tool.

“It’s fun and kind of creepy. It’s like being your own Big Brother,” NPR says. With your permission, the site will pull the From, To, Cc and Timestamp fields of every email you’ve sent from the account. It won’t pull the subject or contents.

Depending on the age and use of your account, this could take some time. I’ve had mine since 2005, and it contains about 40,000 emails. The tool took maybe 10 minutes to process all that.

Once it’s done, you’ll get a map filled with colored bubbles and lines connecting them. The size of the bubble indicates the amount of correspondence with you, while the thickness of the line indicates the amount between the people whose bubbles it connects. You’ll see clusters of bubbles indicating people who tend to get grouped together on emails, and chances are that reflects your relationship with the cluster — they might be from work, or family, or friends.

You can click on any bubble to get more information, such as when the first and most recent email came from that person and how many one-on-one emails have been sent. You can also adjust the time range to map out, which can show how your relationships have evolved over time.

When you get bored or creeped out, the site gives the option to delete all your data and explains how to revoke its access to your account.