Web API growing pains: Loosely coupled yet strongly tied

• An interview with six professional developers to ask them about their experiences with web APIs that evolved.
• A study into the evolution policies of four high-profile web APIs (Google Maps, Twitter, Facebook and Netflix).
• An investigation of ten open source clients integrating the aforementioned four web APIs to see the impact of web API evolution on source code.
• A list of eight recommendations for developers of web APIs and client applications integrating web APIs.
• A study on the code impact on both server and client-side code for both VirtualBox and XBMC.

Web APIs provide a systematic and extensible approach for application-to-application interaction. Developers using web APIs are forced to accompany the API providers in their software evolution tasks. In order to understand the distress caused by this imposition on web API client developers we perform a semi-structured interview with six such developers. We also investigate how major web API providers organize their API evolution, and we explore how this affects source code changes of their clients. Our exploratory qualitative study of the Twitter, Google Maps, Facebook and Netflix web APIs analyzes the state of web API evolution practices and provides insight into the impact of service evolution on client software. In order to complement the picture and also understand how web API providers deal with evolution, we investigate the server-side and client-side evolution of two open-source web APIs, namely VirtualBox and XBMC. Our study is complemented with a set of observations regarding best practices for web API evolution.