# Introduction `xpress-req-validator` allows developers to handle all request validation tasks in a single place as a middleware while respecting the principle of separation of concerns. It can be used at app level or router level. `xpress-req-validator` relies on [Joi](https://github.com/hapijs/joi) (the awsome JSON Schema validator), which is used to define the request validation specs --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://iamthilina.gitbook.io/xpress-req-validator/master.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.