You can now use Vega to create custom graphs in Kibana

Prior to Kibana 6.2, you had to create a custom plugin to create custom visualization types. Now, however, support for Vega is included. Vega is a JSON (HJSON, actually) language that you can think of as a wrapper around the D3 visualization toolkit to allow it to display in Kibana. Here's a video with the highlights:

https://www.youtube.com/watch?v=lQGCipY3th8