"Once you’ve installed the Chrome Apps & Extensions Developer Tool, it will start locally auditing your extensions and apps as you use them," explained Adrienne Porter Felt, a software engineer with the Google Chrome security team.
"For each app or extension, you can see historical activity over the past few days as well as real-time activity by clicking the 'Behavior' link. The tool highlights activities that involve your information, such as reading website cookies or modifying web sites, in a privacy section."
"You can also search for URLs to see if an extension has modified any matching pages," she added. "If you’re debugging an app or extension, you can use the 'Realtime' tab to watch the stream of API calls as an extension or app runs. This can help you track down glitches or identify unnecessary API calls."