This extension give ability to write something like this

http("PostData")
.post(url)
.jsonBody(
  "id" - 23,                    // in json - "id" : 23
  "name",                       // in json it interpreted as - "name" : get value from session variable ${name}
  "project" - (                 // in json - "project" : { ... }
    "id" ~ "projectId",         // in json - "id" : value from session var ${projectId}
    "name" - "Super Project",   // in json - "name": "Super Project"
    "sub" > ( 1,2,3,4,5,6)      // in json - "sub" : [ 1,2,3,4,5,6 ]
    )
  )