Based on robhudson's awesome work (https://github.com/robhudson/django-debug-toolbar) we've created a debug toolbar for Magento. It is installed as a Magento module without hacking Magento's core.

Basic features are implemented and few others will come soon. Check the screenshots for current features: https://github.com/madalinoprea/magneto-debug/wiki

Or demo video on YouTube: http://www.youtube.com/watch?v=aqvgrmebcu4

bash < <(wget -O - https://raw.github.com/colinmollenhour/modman/master/modman-installer)

or

bash < <(curl -s https://raw.github.com/colinmollenhour/modman/master/modman-installer)
source ~/.profile

• For newer Magento versions (1.5.1.0 & above) you just need enable 'Allow Symlinks' from System - Configuration / Advanced / Developer / Template Settings
• For older Magento versions: http://www.tonigrigoriu.com/magento/magento-how-to-fix-template-path-errors-when-using-symlinks/

cd [magento root folder]
modman init
modman clone https://github.com/madalinoprea/magneto-debug.git

• Make sure you've cleaned Magento's cache to enable the new module; hit refresh

I'm pretty lazy and I don't like to create Magento Connect packages. With modman you can effortlessly grab the latest changes from github.

modman update magneto-debug

• Clean Magento's cache to make sure new changes will be enabled.

Extension is not updated regularly. I recommend using modman.

cd [magento root folder]
sudo ./mage install community MagnetoDebug

Magento Connect extension package is available here: http://www.magentocommerce.com/magento-connect/sstoiana/extension/6714/magnetodebug

• Now available in Admin (1.0.1 RC - fancy for I'm laizy to create Magento Connect package)
• Magento module listing; Toggle Magento modules on the fly
• Search configuration keys
• Display peak memory usage, script execution time
• Request information (controller name, action name, cookies variables, session variables, GET and POST variables)
• Models instantiated
• SQL queries executed for current request; ability to see queries' result or queries' execution plan (EXPLAIN)
• List Magento configuration
• Print layout handles for current request
• Find xml files where a specific layout handle is defined
• Created blocks, their associated templates; Preview templates' source code
• Quick actions:
  • Toggle template hints
  • Clear cache
  • Toggle inline translation

We're working to correct these:

• To enable SQL profiler manually you have to add in your local.xml profiler tag <profiler>1</profiler> under connection, like in the example below:

    
        
            
            
            
            
            1
            1
        
    

• Disable SQL Profiler is not working, but Enable SQL Profiler works like a charm (or not)