Valibot and Yup are both JavaScript schema validation libraries that enable runtime type checking and data validation. Yup has been a staple in the React ecosystem for years, offering a fluent API inspired by Joi. Valibot is a newer alternative that prioritizes extreme modularity and minimal bundle size, challenging the traditional monolithic approach taken by Yup and similar libraries.
This comparison matters because validation libraries are foundational dependencies that affect bundle size, developer experience, and runtime performance across your entire application. Yup targets developers seeking a mature, well-documented solution with extensive community resources and framework integrations. Valibot appeals to teams prioritizing bundle optimization, modular architecture, and tree-shaking efficiency, particularly in client-side applications where every kilobyte counts.
Choose Valibot if bundle size directly impacts your business metrics—client-side SPAs, serverless functions with cold start concerns, or mobile-first applications where bandwidth is expensive. The modular architecture also benefits teams building design systems or libraries where consumers should only pay for what they use. The learning curve is steeper due to limited resources, but the TypeScript-first design and functional approach will feel natural to modern JavaScript developers.
Choose Yup for established projects where developer productivity trumps bundle optimization, or when you need proven integrations with React form libraries. If your team values extensive documentation, Stack Overflow coverage, and battle-tested reliability over cutting-edge minimalism, Yup remains the pragmatic choice. The 12.2kB gzipped overhead is negligible for server-rendered applications or admin dashboards where bundle size isn't critical. Don't migrate from Yup to Valibot unless bundle size is a measurable problem.