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What is the difference between OpenAPI 2.0 (Swagger) and OpenAPI 3.0?

OpenAPI 3.0 was a significant restructuring of the specification compared to its predecessor, Swagger 2.0, introducing several structural changes aimed at improving flexibility and reducing duplication.

Swagger 2.0OpenAPI 3.0
Single host/basePath/schemes fields for server info.A servers array, supporting multiple environments and variables.
Separate top-level definitions, parameters, responses sections.Unified under one components object.
Request body described awkwardly via a body-type parameter.Dedicated requestBody object, decoupled from parameters.
One content type assumed per operation via produces/consumes.Explicit content map supporting multiple media types per response.

The requestBody change is one of the most practically significant: in Swagger 2.0, a JSON request body had to be shoehorned into the same parameters array as query and path parameters using in: body, which was conceptually awkward; OpenAPI 3.0's dedicated requestBody object is a cleaner, more intuitive fit for how request payloads actually work.

How is a request body described in Swagger 2.0?
What replaced Swagger 2.0's single host/basePath/schemes fields in OpenAPI 3.0?

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