Nowadays, service-oriented architectures are more popular than ever, and more and more companies and organizations depend on services offered through Web APIs. The capabilities and complexity of Web APIs differ from service to service, and therefore the impact of API errors varies. API problem cases related to Adyen’s payment service were found to have direct considerable impact on API consumer applications. With more than 60 thousand daily API errors the potential impact is enormous. Similarly, API consumers of any API can experience errors, and depending on the application the impact can be costly.

In an effort to reduce the impact of API related problems, we analyze 2.43 million API error responses to identify the underlying faults and derive 11 generic categories that describe them. We quantify the occurrence of faults in terms of the frequency and impacted API consumers. We investigate the impact of API faults on API consumer applications and illustrate this with 3 case studies. Furthermore, an overview is given of the current practices and challenges to avoid and reduce the impact of API errors by API consumers. Using the results, we introduce 16 recommendations for API providers and API consumers to reduce the impact of API related faults.