Intro
Last year when we published the API Economy document, we showed the growth rate of APIs over time. Examining the numbers from the same source — the ProgrammableWeb — in 2012 it appears as if the hockey stick growth of over 100% each year is starting to slow down.
What is really happening?
The numbers
Figure 1 shows the original numbers we published in the Open API Economy report. It shows a compound annual growth rate of roughly 100% each year starting in 2005. The source of the numbers is the ProgrammableWeb.

Figure 1: 100% Annual Growth Rate. Source: The ProgrammableWeb
Figure 2 shows an extrapolation of what the numbers should look like using the same growth rate up to the year 2016. The numbers show approximately 30,000 APIs.

Figure 2: Projected Open API Growth Rate. Source: Craig Burton and Phil Windley
A few days ago, I received an email from a reader who had compiled the numbers from the ProgrammableWeb so far for 2012. Figure 3 shows a graph of the numbers up until the first of May 2012 and it looks like the growth rate is starting to stall.

Figure 3: Open API Growth to May 2012. Source: ProgrammableWeb
I postulated with the reader that key thing to consider here is that these numbers are based open publicly available APIs and not reflect any private API growth at all. And that in all likelihood any glitches that we see in the Open API growth are expected to happen as the private sector catches up or even surpasses the Open API growth.
Of course I have absolutely no empirical data to back up my position. I am just making it up.
However, we had a briefing from 3Scale Networks the other day. 3Scale is a major provider of API development and support technology for both small and large companies. 3Scale’s Dr. Steven Willmott gave an excellent presentation at EIC 2012 about the Open API Economy.
In the briefing — just last week — Steve gave us more insight on what is happening with their customers. Steve pointed out that the largest area of growth for their business was in companies that do not publish their APIs and that are being driven by mobile and tablet app growth.
Their projections show the number of APIs in total — including both private and public APIs — to be somewhere around 250,000. He also said that while they watch the numbers published by the ProgrammableWeb, they also do their own data mining and tracking of API growth.
Now I know that the success of 3Scale’s business depends on a healthy API growth rate. And as such I have to consider discounting somewhat the growth projections they give us. Even so, the growth numbers and logic 3Scale provided in the briefing make a lot of sense and seem to reflect many other indicators and conversations I am having with both customers and vendors.
Summary
I think the slight downturn we see in the Open API growth for the beginning of this year is not a long term trend.
Every other indicator I look at — although none of them are exact science — indicate that if anything the actual growth rate of APIs is still on a steep increase.
Time will tell.
Being definitive on growth is certainly hard – particularly in terms of how long growth will be sustained. As you mention – vendors may have a bias – but we're definitely seeing important trends which might not show in the short-term headline numbers. The first you mention is that many private and semi-private APIs are appearing. In many cases companies are initially launching to a limited partner set and plan to broaden later, or they are launching an API to power their own mobile apps – and then plan to open more fully later (this has given rise to a number of unofficial APis listed by programmableweb: http://blog.programmableweb.com/2011/11/15/the-cu….
The second which we think will be that platforms and frameworks (from PHP/Python/Ruby to open source frameworks like Drupal are making it easier and easier to create APIs without having to code from scratch. This phenomenon has not really hit mainstream yet but it's likely to in the next year or two. This will enable many more people to open APIs that would find it impossible to do so today.
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