How about having unspent outputs show as an edge like any other, but with the destination node having radius zero, so it looks like an edge going nowhere. Then you can show the size of the unspent output using an arrow on the edge.
What about a smaller node with a different shape ?
Edit: I think it would be useful to have the "(unspent)" displayed at all times, not only when moused over. Maybe use a darker colour like #777 or something so it's not too distracting, but still noticeable.
I like it ! Added in the todo list.
You are planning to have an API ?
Yes ! Access to the API is on the roadmap.
Try to add some "interesting" data that the others dont have..
Sure. Actually, I started to work on this tool because existing tools didn't provide data or features I was looking for (interactive charts, privacy-oriented metrics, ...) or are reserved to institutional actors.