Emits one JSON object per log line without replacing Rails.logger. Existing calls keep working: strings become the "message" field, hashes are merged as fields, and exceptions are expanded into a structured "error" object. ActiveSupport::TaggedLogging stays fully functional, and registered tags of the form "name=value" are promoted to first-class JSON fields instead of being flattened into a "[name=value]" message prefix. Optional log subscribers replace the framework's prose output with typed fields.