Tooltip overflow

Tooltip overflow diagram width. Can i make it shown one line ?

I assume you mean more than one line, not “one line”.
I suggest that you set the TextBlock.maxSize to something like new go.Size(250, NaN).

So, i still wonder is it possible show that text ‘one line’ even though it’s out the diagram width?

So you want the text to get smaller in order to fit in the available space?
You can either calculate it, or you can use a “Viewbox” Panel, which will compute the scale for you automatically:

I think this what i’m talking about, i want tooltip text always be shown, it seem available when use ‘HtmlInfo’ instead of ‘$(‘ToolTip’)’.

If you want something to extend beyond the HTMLDivElement that is hosting the Diagram, you will need to use HTML.