To enable the developer dashboard in 2013 is fairly simply, so long as you’re willing to delve into PowerShell.
The developer dashboard toggle in SharePoint 2013 – This is OFF by default in your farm, you will NOT see this unless you turn on the developer dashboard at the farm level.
The developer dashboard in action
Note: You can enable it (On) or disable it (Off) by using Powershell (the Ondemand option is deprecated in SharePoint 2013)
To enable the developer dashboard, open the “SharePoint 2013 Management Shell” and type the following:
[sourcecode language=”powershell”]
$content = ([Microsoft.SharePoint.Administration.SPWebService]::ContentService)
$appsetting = $content.DeveloperDashboardSettings
$appsetting.DisplayLevel = [Microsoft.SharePoint.Administration.SPDeveloperDashboardLevel]::On
$appsetting.Update()
[/sourcecode]
To disable the developer dashboard, open the “SharePoint 2013 Management Shell” and type the following:
[sourcecode language=”powershell”]
$content = ([Microsoft.SharePoint.Administration.SPWebService]::ContentService)
$appsetting = $content.DeveloperDashboardSettings
$appsetting.DisplayLevel = [Microsoft.SharePoint.Administration.SPDeveloperDashboardLevel]::Off
$appsetting.Update()
[/sourcecode]
Another good reference is the following: http://sps2013.blogspot.ca/2012/07/developer-dashboard-in-sharepoint-2013.html