broken-config.json

{
  "retry_interval": 20,
  "sys_interval": 10,

  "listeners": {
    "port": 1883,
    "max_connections": -1,

    "auth_plugin": 
      "plugin_path": "auth-plug.so",
      "backends": "mysql",
    }
  }

broken-config.lua

retry_interval = 20
sys_interval = 10

listeners = {
  {
    port = 1883,
    max_connections = -1,

    auth_plugin = 
      plugin_path = "auth-plug.so",
      backends = "mysql",
    }
  }
}

broken-config.yaml

retry_interval: 20
sys_interval: 10

listeners:
  one:
    port: 1883
    max_connections: -1
    
    auth_plugin
      plugin_path: "auth_plug.so"
      backends: "mysql"

What happens in broken situations

~/Scra+/ralight-configs $ python3 -c "import json; print(json.load(open('broken-config.json')))"
[snip]
json.decoder.JSONDecodeError: Expecting ',' delimiter: line 10 column 20 (char 151)

~/Scra+/ralight-configs $ python3 -c "import yaml; print(yaml.safe_load(open('broken-config.yaml')))"
[snip]
yaml.scanner.ScannerError: while scanning a simple key
  in "broken-config.yaml", line 9, column 5
could not found expected ':'
  in "broken-config.yaml", line 10, column 18

~/Scra+/ralight-configs $ lua broken-config.lua 
lua: broken-config.lua:10: '}' expected (to close '{' at line 5) near '='