What is the difference between Jest and Vitest?

Both are JavaScript test runners with similar APIs for describe, it, expect and mocks. Vitest is built on Vite, reusing its config, plugins and transforms with native ES modules and TypeScript, while Jest is the long-established runner with its own module system and transformers.

Largely. Vitest's API mirrors Jest's, with vi in place of jest for mocks and timers, so many test files migrate with small changes such as replacing jest.fn with vi.fn and adjusting config.

For projects already using Vite, new TypeScript or ESM codebases, monorepos that want fast watch mode, and when you want the test transform pipeline to match the app's build.

For large existing Jest suites, React Native projects where Jest is standard, or when tooling and team knowledge are built around Jest and migration has little payoff.

Vitest supports ESM and TypeScript natively through Vite. Jest historically needed Babel, ts-jest or SWC transforms and has had more friction with pure ESM packages.

Jest uses jest.fn, jest.mock and jest.spyOn; Vitest uses vi.fn, vi.mock and vi.spyOn. Vitest hoists vi.mock calls similarly, and both support module factories and automatic mocking.

Vitest is often faster, especially in watch mode, because it reuses Vite's transforms and module graph to rerun only affected tests. Jest is solid, and its parallel workers handle large suites well.

Jest uses jest.config with transforms, moduleNameMapper and test environment. Vitest uses a test section in vite.config or vitest.config, inheriting aliases and plugins from Vite.

Both run in Node or jsdom (and happy-dom for Vitest). Vitest also has a browser mode that runs tests in real browsers through Playwright or WebdriverIO.

Both support snapshot and inline snapshot testing with similar commands, and Vitest's snapshot format is compatible with Jest's.