jq is such a good being that it allows you to make sense of your crowded, stringified and escaped json messages, which you may collect via logstash, if you desire:

logstash agent --quiet | jq -S '.foo | fromjson | {custom_label: .["@rubydebug_label"], another_custom_label: .["@another_rubydebug_label"], yacl: .["@yarl"].subfield, you_get_the_idea: true'