mmh, much more clear now, yes. So you need to deal with a perl part and a lisp part

joining some dots that could (or not) to be useful for you

If you want to pick-up error messages from json, maybe you could wish to explore the functions available in the json package. i.e json-error

(require 'json) 
;; create data lisp structures from json files
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or, in emacs...

m-x load-library json
apropos json
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