Inter-parameter Constraints in Contemporary Web APIs

Today’s web applications often rely on a myriad of external web APIs, communicating with them through various HTTP requests spread throughout the application. These APIs are often textually described by constraints on the inputs and outputs of their entry points. In this paper we discuss constraints in web APIs that span multiple parameters. We show that these constraints are common in web APIs, but cannot be expressed in existing machine-readable API specification languages. We envision the emergence of constraint-centric specification languages which focus on expressing constraints and describe a prototypical language that supports constraints over multiple parameters.