One of the coolest features I think we’ve added in Visual Studio 2010 is the ability to add your own tabs into the webtest playback view. Extending the user interface in this way allows you to do data analysis and have it pop up right in front of you in whatever format you want. No more exporting to excel or whatever your favorite analysis tool is, just compile everything you one in one place and voila! That being said, I have been told that it can be difficult to grok at first glance. So, I wanted to post a sort of ‘how to’ in order to get one of these working. A colleague of mine suggested that I could use this forum to demonstrate how to keep track of something that affects the performance of many users’ websites. Namely, Viewstate. So, below is a step by step instruction on how to create a webtest playback tab which keeps track of the viewstate size for each request. Step 1: Create the add-in project Visual Studio Add-ins have their own special type of project, you can find it under “Other project types / Extensibility”. I’ve named mine “ViewstateAddin”. Step 2: Walk through the create add-in wizard When the wizard launches, you’ll be add a “welcome” screen. Click next to move to page 1.