Ur, also called Ur/Web, is a multi-paradigm, high-level, pure, strict, functional programming language. It is a dialect of the language ML, designed for web development, created by Adam Chlipala at the Massachusetts Institute of Technology that one program can emit code for a server, web browser client, and SQL specific to a given database backend. The full implementation is free and open-source software released under an MIT License.

Ur has its start and roots in a superseded progenitor language named Laconic/Web, in 2006.

Ur supports a powerful kind of metaprogramming based on row data types.

Ur/Web is Ur plus a special standard library and associated rules for parsing and optimizing. Ur/Web supports construction of dynamic web pages and applications backed by SQL databases. The signature of the standard library is such that well-typed Ur/Web programs "don't go wrong" in a very broad sense. They do not crash during particular page generations, and may not:

This type safety is just the foundation of the Ur/Web methodology. It is also possible to use metaprogramming to build significant application pieces by analysis of type structure.

The Ur/Web compiler also produces very efficient object code that does not use garbage collection.

SQL syntax templates embedded in the language facilitate the handling of tables.

Although the syntax is based on Standard ML the language includes concepts from Haskell with added type manipulation.