The T4 Editor for Visual Studio 2013 is a comprehensive T4 editor that makes creating and editing templates relatively simple, and the add-in does this with IntelliSense, syntax highlighting, and even code outlining, for a relatively well-rounded program that makes Visual Studio 2013 much easier to work with.
Of note, the T4 Editor utilizes IntelliSense, which includes all Visual Studio C# and Visual Basic IntelliSense features, such as parameter info, tooltips, code completion, and also supports a completion list to be used for template directives. T4 Editor for Visual Studio 2013's IntelliSense also works to list all available C# classes and its members, including ones that are found in referenced assemblies and template files, making things easy to sort through and work on.
Additionally, T4 Editor has a powerful syntax highlighting system, which highlights template directives and C#/Visual Basic code, making it easy to distinguish regular text from function calls. Best of all, fonts and colors can be completely customized for any Visual Studio code editor, letting you choose from a good assortment of colors and fonts to differentiate what you're working on. You can even enable or disable intellisense, word wrapping, line numbers, virtual whitespace, and so on, in addition to customizing intelligent indenting, allowing for a breadth of customization that'll make any T4 Template work the way you want it to work.
With the Goto function, T4 Editor lets you jump quickly to definitions and declarations of objects/members, so long as they're included in the selected template file. And with a multilevel template including all classes from selected templates are available in IntelliSense, which you can navigate to with the aforementioned Goto command. T4 also supports automatic template formatting, via a format that's run both intelligently and efficiently.
So far, my biggest complaint seems to be the dark mode theme, which makes text all but unreadable. Outside of that, T4 Editor works well as a fast, efficient, and highly customizable plug-in that makes T4 template editing a little simpler and quicker. T4 Editor for Visual Studio 2013 is also included as a part of Entity Developer, which is a powerful modeling/code generation tool for ADO.NET Entity Framework, LinqConnect, NHibernate, and LINQ to SQL. For what you get, it's a powerful tool and all that's required to run T4 in Visual Studio 2013, making it very simple to install and use right out of the box.
Create and edit Visual Studio T4 templates with intellisense