jq - Create json from scratch

How do I create a json structure from scratch using only jq?

The command line option --arg name value

passes a value to the jq program as a predefined variable… so --arg foo 123 will bind $foo to "123" - https://stedolan.github.io/jq/manual/

These named arguments are also available from $ARGS.named. Found via https://stackoverflow.com/a/59769162

The snippet below creates a json structure that you can pipe to a file. It also prints the contents of $ARGS to show what arguments are named and which are positional

$reponame="awesome-repo"
$branchname="main"

jq -n '{github_meta: {reponame: $reponame, branch_name: $branchname }, feature: {}, all: $ARGS}' \
  --arg reponame "$reponame" \
  --arg branchname "$branchname" \

# output
{
  "github_meta": {
    "reponame": "awesome-repo",
    "branch_name": "main"
  },
  "feature": {},
  "all": {
    "positional": [],
    "named": {
      "reponame": "awesome-repo",
      "branchname": "main"
    }
  }
}