Interesting tool — visualizing routing rules is something many people underestimate until they actually have to decode a complex fare. The ExpertFlyer add-on angle makes a lot of sense.
A couple of questions out of curiosity: how does Routing Ruler handle highly permissive rules where EF itself already returns a lot of edge-case routings? And do you plan to add any filtering or weighting logic (e.g. practical vs theoretical routings)?
Also good to see KVS compatibility — that should make it more useful for people who already rely on it in their workflow.