Doesn't exist.

While some airlines publish award availability to GDS’s (which in turn offer API access for a non-trivial fee), plenty more do not. This is why tools like KVS have resorted to scraping websites, often without the knowledge or permission of the sites they target.

Even if you access this award availability data via a GDS API, airlines do not publish anything to GDSs that would let you price award itineraries, nor obtain conversion rates from transfer partners. And airlines are also not about to make this data available via their own APIs.

People have attempted to build multi-airline award search engines in the past, often with the goal of finding the lowest cost across programs. These tools usually rely on the creator taking each airline’s award charts and known data about conversion rates and maintaining an internal set of logic. Sometimes these tools operate without availability data at all, and only attempt to show the lowest price between two cities based on an award chart comparison.

But with incomplete availability data, and internally-maintained copies of award charts quickly falling out of date as programs change (especially as programs eliminate award charts and move towards dynamic award pricing), these tools all ultimately meet the same end. The ones that survive are the ones that narrow their focus.