Yajl-tcl, a Tcl C extension written to bring the capabilities of the Yet Another JSON Library (YAJL), a C library for parsing and generating JSON, available to Tcl coders. JSON stands for Javascript Object Notation, a popular data exchange format for Javascript.

Although there is already a package in the tcllib library, that can generate JSON, the big advantage in using yajl-tcl is performance. Also, yajl-tcl can parse JSON as well as generating it.