The "demjson" module, and the included "jsonlint" script, provide methods for encoding and decoding JSON formatted data, as well as checking JSON data for errors and/or portability issues. The jsonlint command/script can be used from the command line without needing any programming.

Although the standard Python library now includes basic JSON support (which it did not when demjson was first written), this module provides a much more comprehensive implementation with many features not found elsewhere. It is especially useful for error checking or for parsing JavaScript data which may not strictly be valid JSON data.