There is no killer text summarization API, yet….
Mashape seems to have the most summarization APIs in one place:
· List of 30+ Summarizer APIs, libraries, and software
See my recent “survey” of Github resources on summarization:
100 Best GitHub: Automatic Summarization | Meta-Guide.com
See also my various Quora answers on summarization:
quora.com/search?q=endicott+summarization
And while you’re about it, why not read the success story of Nick D’Aloisio….