From the creators of the Inventory Spy Google Chrome extension:
We now have developed a helpful tool that Amazon sellers can use to track the keyword/search term rankings of their PL products. Since more sales come organically when you're ranking highly for your main search terms, it's important to track where your products stand on a daily basis when customers are searching for your keywords. By monitoring your product ranks daily, you'll gather key insight in to how changes in your PPC spending or product descriptions affects your rankings.
This is a tool that all PL sellers should use daily to stay on top of their competition!
More Amazon selling tips at the Wix site