Use data annotations in your model to place a tooltip in the Description property of the DisplayAttribute attribute.
Then create your own Html Helper function that places the Description property in the title attribute of the TextBox input field. You can call the TextBoxWithTooltipFor helper
In your definition, you can replace the call with @ (Html.TextBoxFor (...)) with the call @ (Html.TextBoxWithTooltipFor (...))
Here is the code that has been tested and works. 
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