DataForSEO

DataForSEO API is designed for SEO-software companies and agencies. With DataForSEO users can build SEO-software, from a simple rank tracking solution to an enterprise-level SEO platform. DataForSEO's main products are SERP API, Keywords Data API, and DataForSEO Labs API. Using DataForSEO APIs, users get such data as rankings, Search Volume, Top 100 results from search engines, On-Page data and much more.

The vendor states they've made their project live because they believe they can help companies fill their SEO-data needs better than any alternative.