The other day I enabled Time Machine backups on my Mac and after a few exclusions (e.g. my virtual machines) I had a backup of about 40 GB to do.

Today after a day in the office I noticed that the next backup would take 600 MB. This made me wonder what actually was backed up and why that much data had changed.

After some google searches I found the tool timedog on google code. By using this tool as described on their web you can find out exactly which files were backed up in the last backup and how much space they take up. Using this knowledge I could tune my Time Machine exclusions further.

Small addition though: if your Time Machine is on the network you will first have to have it mounted so that it appears as Time Machine Backup under the Devices node in a Finder windows. This is easiest done by right clicking the Time Machine icon in your menu bar and then selecting Enter Time Machine. This will mount your backup as a device and take you into your Time Machine. When exiting your Time Machine your backup will still be mounted and thus be accessible for use with the timedog tool.

Enjoy.