NppGraphViz

A Notepad++ plugin that sends the current tab's document to a GraphViz preview window.

Installation

Install Notepad++

Notepad++ is a powerful text editor that supports plugins such as NppGraphViz. Go to the Notepad++ homepage at https://notepad-plus-plus.org. Download and install the latest version.
Install Graphviz

Graphviz is a collection of progams that make diagrams from a simple text language. Go to Graphviz's homepage at www.graphviz.org. Download and install the latest version.
Install NppGraphViz

If you installed 64-bit Notepad++, then download the 64-bit NppGraphViz.dll

If you installed 32-bit Notepad++, then download the 32-bit NppGraphViz.dll

Make a "NppGraphViz" folder in Notepad++'s plugins directory, and move the NppGraphViz.dll into it. On a typical install, the full path would be "C:\Program Files\Notepad++\plugins\NppGraphViz\NppGraphViz.dll" or "C:\Program Files (x86)\Notepad++\plugins\NppGraphViz\NppGraphViz.dll"
Start Notepad++

Start Notepad++. Click "Plugins" from the file menu, you should see "Graphviz" if the plugin successfully installed.

Hit the F9 key to preview or refresh your current tab's document with a selected GraphViz program (e.g. dot.exe).
Save the image with any of GraphViz's supported file types.
Zooming and dragging. The mouse wheel adjusts the zoom. Holding down the left or right mouse button allows dragging the preview image. The middle mouse button resets the preview.

Suppose you have this text in Notepad++:

Digraph g
{
    Stop->Collaborate
    Collaborate->Listen
}

The plugin sends the text to GraphViz, and displays the following preview:

NppGraphViz does not add syntax highlighting, but that functionality is available here: https://github.com/signmotion/graphviz-syntax-highlighting