BDD

BDD (Behavior-Driven Development) grew out of test-driven development as a way to describe what software should do in language the whole team can read. Instead of starting from implementation details, you start from a scenario — Given some context, When something happens, Then this is the expected outcome — and that scenario doubles as both the specification and the automated test. For APIs, it turns fuzzy expectations about a request and its response into concrete, runnable assertions.

• Given/When/Then scenarios - A structured, near-plain-English grammar (popularized by Gherkin and Cucumber) that stays readable to non-developers while remaining executable.
• Shared understanding - Product owners, engineers, and QA agree on behavior before code is written, closing the gap between what was asked for and what gets built.
• Executable specification - Each scenario is a living test; when it passes, the documented behavior is provably true, and when it fails, the gap is obvious.
• Outside-in design - You define the desired behavior of the interface first, which pushes API design toward what consumers actually need.

In API operations, BDD assertions describe the contract from the consumer’s point of view and then verify it continuously — a natural companion to OpenAPI-driven contract testing and monitoring. I have used behavior-driven assertions in my own API research to validate that a response is not just structurally valid but behaviorally correct against a stated expectation. As agents increasingly consume APIs, plain-language Given/When/Then scenarios also become a clean, machine-readable way to express and check the behavior an agent should be able to rely on.