ipuz is intended as an openly-documented format for data files of puzzles such as crosswords and sudoku. In contrast to "proprietary" formats such as PUZ, there is an official spec available freely and released under a Creative Commons license (BY-ND 3.0), instead of the format having to be discovered by reverse engineering subject to possible hassles by intellectual-property owners. It was created and released by the puzzle technology company Puzzazz, which was the first company to use it.
ipuz data is expressed in JSON format.
ipuz files should specify the version within legal JSON. Expected values include:
"version": "http://ipuz.org/v1" and
Although ipuz is not an XML-based format, its creators borrowed the "namespaces designated by URIs" concept for identifying subtypes of the format for different sorts of puzzles. Several puzzle types, with associated URIs in ipuz.org, are defined in the spec, and others may define puzzle types of their own and assign them identifying URIs within their own websites. The spec requires that anybody defining a puzzle type and assigning it a URL actually own the site within which that URL resides, but doesn't mandate that it actually resolve to anything useful; however, it is suggested that it lead to a description of the puzzle format in question. The URIs referenced in the original spec all seem to redirect to the spec document itself, rather than any more specific part of it related to a particular puzzle type.
The types defined in the spec are:
http://ipuz.org/fill(grid puzzle to fill in)