jc has many parsers for the specific output format of various programs, it can automatically create a JSON object structure using its knowledge of each format.

jb doesn't have high-level knowledge of other formats, it can read from common shell data sources, like command-line arguments, environment variables and files. It gives you ways to pull several of these sources into a single JSON object.

jb understands some simple/general formats commonly used in shell environments:

- key=value pairs (e.g. environment variable declarations, like the `env` program prints

- delimited lists, like a,b,c,d; (but any character can be the delimiter) including null-delimited (commonly used to separate lists of file paths)

- JSON itself — jb can validate and merge together arrays and objects

You can use these simple sources to build up a more complex structure, e.g. using a pipeline of other command line tools to generate null-delimited data, or envar declarations, then consuming the program's output via process substitution <(...). (See the section in the README that explains process substitution if you're not familiar, it's really powerful.)

So jb is more suited to creating ad-hoc JSON for specific tasks. If you had both jc and jb available and jc could read the source you need, you'd prefer jc.