=== Relationships to software engineering practices ===
The paradigm of agreeing on an API contract first and then programming business logic afterwards, in contrast to coding the program first and then writing ana retrospective description of its behavior as the contract, is called contract-first development. Since the interface is determined before any code is written, downstream developers can [[Mock object|mock]] the [[Server (computing)|server]] behavior and start testing right away.<ref>{{Cite book |last=Preibisch |first=Sascha |url=https://www.worldcat.org/oclc/1076234393 |title=API development : a practical guide for business implementation success |date=2018 |isbn=978-1-4842-4140-0 |___location=[Berkeley, CA] |oclc=1076234393 |quote=Having the Swagger (or for that matter, any other machine-readable) document available, team members can start working on their part of the project at the same time.}}</ref> In this sense, contract-first development is also a practice of [[shift-left testing]].
