Swagger Express Middleware is a Node.js library that plugs into an Express server to automatically parse, validate, and mock APIs defined by Swagger 2.0 (OpenAPI 2.0) specifications. It provides ready‑made middleware for metadata injection, request parsing, validation, CORS handling, serving the API definition, and zero‑code mock implementations, making it useful for API developers who want rapid prototyping, testing, or documentation of their Swagger‑based services.