Karthus Runes explained
There's one set of runes for Karthus on patch 14.9 that is the clear favorite for LoL players and pros alike. The best Karthus rune paths on the position 
Jungle are 
Inspiration as the primary path and 
Domination as the secondary path with a pick rate of 56%. Besides picking runes on Karthus you should learn how to play Karthus and if you are interested in pro matches take a look on how a pro builds Karthus. If you want to discuss 
Karthus then you should visit the champion subreddit.
Karthus runes from primary path
Inspiration opens creative opportunities on Karthus troughout the match. Most of high elo players – and our LoL pros in the the major regions – have agreed that First Strike is the best keystone rune to run on Karthus. Other primary runes on Karthus are Magical Footwear, Future's Market and Cosmic Insight.
Magical Footwear allows Karthus to focus on those essential core items without the need to spend the additional 300 gold on boots. You can enter debt to buy items, which is displayed as negative gold in your inventary. A small lending fee is added onto the amount of gold you owe after leaving the shop. Cosmic Insight grants summoner spell and item haste.
Karthus runes from secondary path
When it comes to your secondary path, most Karthus players prefer to go with Domination. Domination improves burst damage and assassination tools on Karthus. On the Domination path, the best runes for Karthus are 
Ultimate Hunter and 
Eyeball Collection.
Ultimate Hunter scales up Karthus ultimate haste on every unique champion takedown. Eyeball Collection is next up. This grants the user additional damage with every killing they score.
FAQ for Karthus Runes
Which is the best keystone rune on Karthus?
The best keystone rune on Karthus is First Strike. This Karthus runes setup is then referred as Karthus First Strike.
What runes does Karthus use?
Runes from the paths Inspiration and Domination are the most used runes on Karthus. For the exact pick rates of Karthus runes used, you have to study the rune distribution presented.