KPIs for APIs: Developer Experience Can Make or Break Your API

This is the second post of a three-part series covering key performance indicators for APIs, based on John Musser's presentation at the Business of APIs Conference.

The first post of this three-part series about key performance indicators (KPIs) for APIs covers outdated methods of measuring API success, reasons for having an API, types of KPIs for APIs and what should drive a company's KPIs. This post, the second of the series, covers developer funnels and potential KPIs, measuring the app ecosystem, and how developer experience can make or break your API. This three-part series of posts is based on John Musser's presentation at the Business of APIs Conference (BAPI) held earlier this month in New York City and can be viewed in its entirety on SlideShare.

Developer experience ( DX) has become a hot topic, especially when it comes to APIs. It was a topic of discussion at the 2014 DeveloperWeek conference in San Francisco, it was discussed at the recent ProgrammableWeb API conference in London, and it was covered in several sessions at the recent API Strategy & Practice Conference. In addition, ProgrammableWeb recently published an article about how DX is the key to a successful API.

It is important that a company providing APIs engage with the developer community and measure KPIs that will help determine if its API program is a success with developers and is benefiting the company as a whole. In an article published last year on ProgrammableWeb, Mark Boyd wrote:

There is a developer skill shortage around the world and a growing number of open APIs being made available. So businesses are finding they must offer an accessible and enjoyable experience for developers who are at the frontline of using a business' API. It has become a key measure of a business' API success.

We reached out to Musser, founder of API Science and ProgrammableWeb, who explained the critical importance of DX when it comes to APIs:

Just as in the evolution of websites where companies learned just how important User Experience ( UX) is, companies are now learning how critical great developer experience is. If your website doesn't have solid UX, your sales, conversions and all downstream metrics suffer. If your API doesn't have great DX, then your developer registrations, API usage, revenue and any downstream metrics suffer as well.

Know Your Developer Funnel


All websites that have a conversion target have a funnel that forms a path toward a specific goal. There are dozens of website models, and one example is from Dave McClure's "Startup Metrics for Pirates" that defines the funnel path as acquisition, activation, retention, revenue and referral.

APIs also have funnels, and the website funnel defined by venture capitalist Dave McClure is similar to an API developer funnel:

  • Acquisition How do developers find you?
  • Activation— Did the developer have a good first experience?
  • Retention Do developers return? Did they get an API Key? Are they building anything?
  • Revenue How do you and developers make money?
  • Referral Do developers tell others?

When it comes to a developer funnel, many potential KPIs can be measured:

  • Acquisition Developer Portal site: sources, traffic volume, uniques
  • Activation Number of developer API registrations, number of API keys issued
  • Retention Number of active developers, API call volume by developer, number of apps
  • Revenue Dollars per developer, dollars per app, number of end users
  • Referral Number of developer referrals, developer/app growth, Net Promoter Score

There are many things to keep in mind when it comes to APIs and developer experience. While developer experience is subjective, qualitative metrics, such as user testing, surveys, forums and social media, can be used to measure the effectiveness of your API program with developers. Another important metric for both internal and external developers is the time it takes to get to the first "hello world." What is the average time for developers to get up and running with your API?

Measure the API Ecosystem


A good developer experience will help create word-of-mouth advertising for your API, increase adoption rates, increase the developer engagement level, build developer loyalty and perhaps even inspire developer evangelism for the API. All of these things help to ensure a healthy and growing API ecosystem. It is important that API ecosystem KPIs are measured regularly:

  • App users Total app users, revenue per user, user growth rate, user churn
  • Apps Total apps, trending apps, revenue per app, channel (mobile/Web)
  • Developers Total developers, active developers, revenue per developer, top developers, stuck developers
  • Your APIs Total API calls, top API calls, top API packages, internal usage
  • You Total revenue, total partnerships, market share innovation

Developer Experience Can Make or Break Your API

When it comes to APIs, developers are the customers. The number of APIs available today far exceeds the number of developers available to use them. Knowing your developer funnel, measuring potential KPIs and the API ecosystem are important parts of a successful API strategy and help ensure that your API provides a positive experience for developers.

The Next Post

The final post in this three-part series will cover different aspects of measuring API success and return on investment, as well as real-world examples of KPIs for APIs.

Be sure to read the next Analytics article: KPIs for APIs: Measuring API Success, Real World Examples