Mentoss

Mentoss is a lightweight, TypeScript-first utility for mocking fetch() requests and responses in Node.js (>=18.18) and browser environments. Version 0.13.0 (July 2024) provides three core classes — MockServer, FetchMocker, and MockAgent — to define server routes, replace global fetch, and intercept undici requests. Unlike similar libraries (e.g., nock, msw), Mentoss focuses exclusively on fetch() and undici, supporting both ESM and CommonJS through conditional exports, shipping type definitions, and offering a minimal API with built-in route tracking and assertion helpers. The package is authored by Nicholas C. Zakas (ESLint creator) and has a release cadence of approximately monthly updates.