yup

Yup is an informal English interjection used to express affirmation or agreement. It is a casual counterpart to “yes” and is commonly heard in spoken American English. Spelling variants include “yep” and “yeah”; “yup” tends to convey a straightforward, slightly more emphatic yes.

In computing, Yup refers to a JavaScript library for schema validation and data transformation. It provides a fluent, chainable API for defining schemas that describe the shape and constraints of values, enabling validation on both client and server sides. Yup supports basic types such as string, number, boolean, date, array, and object, as well as nested schemas, required and optional fields, length and range checks, pattern matching, emails and URLs, and enumerations. It also supports asynchronous validation and conditional rules, plus transformations and default values, making it popular for validating form data in modern web applications.

Yup is designed to be browser-friendly and framework-agnostic, with particular adoption in React ecosystems where form libraries integrate it for validation. Its API is inspired by Joi, offering a readable style of schema construction while emphasizing front-end validation and runtime type inference. Schemas created with Yup can be reused across multiple forms and endpoints, helping maintain consistent validation logic throughout an application.