I like it, one piece of feedback I have is - the export to PNG button, I wasn't expecting it to be a screenshot of the JSON, I thought it would be the graph; at least to me that would make more sense... paste JSON, see graph, export image of graph. What do you think.

I agree with this. Since it's rendered as an SVG, saving it as an SVG would be great. PNG as backup perhaps.

Looks great! Thanks OP for sharing!

Thanks for the feedback, the option to take a snapshot of the graph sounds good, I will add it to the TODO