If you are trying to find a good free tool to help with performance tuning your WebSphere Application Server environment, then I think this is a great start. IBM provides this very simple and easy to use tool. After you download (see URL below) and unzip, all you need to do is tell the tool a Deployment Manager to connect to and you can begin viewing PMI data and tuning your environment.

Once you launch the tool, you will be presented with a welcome screen (I had to block out some server names):

You can click on the Add New Host button and specify the server information that you wish to monitor:

You will then see the host in the Hosts section on the upper left. If you double-click on this, it will connect the Deployment Manager and begin taking snapshots of the environment (at 1 minute intervals by default, which you can change):

The tool captures a lot of detailed information which you can then use to tune your environment accordingly. The bottom portion of the screen allows you to see a variety of tuning parameters and what their current values are. You can even change these values from here and it will be saved to your environment:

This tool is definitely worth a download if you need a free and easy to use monitor to begin tuning your environment. Along with monitoring your environments, the Tuning Toolkit records these snapshots and allows you to generate a report highlighting areas that need to be researched and tuned.

You can download it here: