It started as a simple collection of WSGI application utilities and has evolved into one of the most powerful WSGI utility libraries. Flask wraps Werkzeug, allowing it to take care of the WSGI intricacies while also offering extra structure and patterns for creating powerful applications.
Werkzeug is a WSGI utility library for Python.
Werkzeug (German for "tool") is a BSD-licensed utility package for the Python programming language, essentially a toolkit for Web Server Gateway Interface (WSGI) applications. Software objects for request, response, and utility functions can be created with Werkzeug.
Werkzeug is a WSGI web application library with a lot of features. There are no dependencies enforced by Werkzeug. The developer has complete control over the template engine, database adapter, and even how requests are handled.