Editor's note: Be sure to check out our research on the overall growth of Web APIs since 2005. At the time of writing, this is the most recent data we have, but check the research page to see if we have a more updated article. We will be continually updating the overall growth chart with other charts getting updated on a less frequent basis.
Of the more than 22,000 APIs that ProgrammableWeb tracks in our directory, which one is the most popular? It's a question that can be answered in many ways. We could look at the number of calls made to each API however, most providers prefer to keep that a secret, and when they do publicize the numbers, they often aren't shared in a consistent manner. We could look at it from a community point of view using data such as the number of Github commits an API has.
There are other ways that let us leverage the data in our directory. In a past research article, we discussed how we can track the number of times a user follows an outbound link from one of our profiles to an API provider’s site.
Every API on ProgrammableWeb also has a track functionality that allows developers to receive updates on them through our weekly personalized Watchlist. In fact, our Watchlist service is the most popular feature that ProgrammableWeb's registered users take advantage of.
By looking into the tracking data, we can get a glimpse at the content including APIs and SDKs that our readers are most interested in. We did just that, a few years ago when we wrote about the most popular APIs. It feels like a good time to go back and revisit the data to see if anything has changed since then.

We see that seven of the top ten APIs have remained the same with the ever popular Facebook and Google Maps leading the way. Of the three new APIs in the top ten, Weather Channel and Yahoo Weather are no surprise as Weather has long been a popular category.
While this provides a sense of the APIs that have endured in popularity over time, we thought it would be interesting to see what APIs have gotten the most interest recently. This research article was last updated in September of 2017. The table below shows both the top tracked APIs up to September 2017, and the top tracked APIs in the two years since then. The APIs highlighted in yellow are those that appear in both lists. The ones highlighted in green are the APIs that were not as highly ranked two years ago, but have seen a rise in popularity since then.
3,266 | Google Maps | 561 | |
Google Maps | 2,710 | 530 | |
1,836 | BetfairTrack this API | 414 | |
YouTube | 1,382 | Weather Channel | 411 |
AccuWeather | 1,369 | Instagram Graph | 371 |
1,148 | NetflixTrack this API | 347 | |
Amazon Product Advertising | 938 | YouTube | 337 |
Weather Channel | 884 | SoundCloudTrack this API | 334 |
Yahoo Weather | 837 | OpenStreetMapTrack this API | 327 |
SkypeTrack this API | 773 | Rotten TomatoesTrack this API | 312 |
Pinterest DomainTrack this API | 682 | India Goods and Service Tax (GST)Track this API | 303 |
KayakTrack this API | 672 | AccuWeather | 297 |
FlickrTrack this API | 661 | Yahoo Weather | 295 |
Instagram Graph | 652 | 274 | |
FedExTrack this API | 603 | FitbitTrack this API | 251 |
The data shows that just over half of the most tracked APIs from two years ago remain popular. Twitter and Instagram join Facebook to yet another example of the powerful draw that social platforms have for developers. Weather APIs also make a strong appearance with three APIs in the top 15. For a deeper look at the category be sure to read our list of the top weather APIs. YouTube, an API that we have previously reviewed also made the list.
One interesting API that has risen in tracking popularity is the Betfair API. In light of the 2018 Supreme Court ruling that overturned a federal ban on sports gambling, it will be interesting to see if increased opportunities for legalized gambling leads to greater interest in gambling APIs.
Did your API make the list? If you are a provider adding a listing in our directory is a great way to improve the discoverability of your APIs and raise awareness of your program. If you would like to include your APIs in our directory, you can use the link below.