jq is a command-line JSON processor.
If you want to learn to use jq, read the documentation at http://stedolan.github.io/jq. This documentation is generated from the docs/ folder of this repository.
If you want to hack on jq, feel free, but be warned that its internals are not well-documented at the moment. Bring a hard hat and a shovel. Also, read the wiki: http://github.com/stedolan/jq/wiki
If you're building directly from the latest git, you'll need flex and bison installed. To build, run:
autoreconf
./configure
make
After make finishes, you'll be able to use ./jq. You can also
install it using:
sudo make install
If you're not using the latest git version but instead building a
released tarball (available on the website), then you won't need to
run autoreconf (and shouldn't), and you won't need flex or bison.