diff --git a/src/BitLogger_test.mbt b/src/BitLogger_test.mbt
index 6b1cf19..d2de2dc 100644
--- a/src/BitLogger_test.mbt
+++ b/src/BitLogger_test.mbt
@@ -268,6 +268,92 @@ test "config subtype json helpers stringify stable shapes" {
   )
 }
 
+test "config json helpers export stable structured shapes" {
+  let queue_json = queue_config_to_json(
+    QueueConfig::new(8, overflow=QueueOverflowPolicy::DropOldest),
+  )
+  let queue_obj = queue_json.as_object().unwrap()
+  inspect(@json_parser.stringify(queue_json), content="{\"max_pending\":8,\"overflow\":\"DropOldest\"}")
+  inspect(queue_obj.get("max_pending").unwrap().as_number().unwrap().to_int(), content="8")
+  inspect(queue_obj.get("overflow").unwrap().as_string().unwrap(), content="DropOldest")
+
+  let formatter_json = text_formatter_config_to_json(
+    TextFormatterConfig::new(
+      show_timestamp=false,
+      show_level=true,
+      show_target=false,
+      show_fields=true,
+      separator=" | ",
+      field_separator=",",
+      template="[{level}] {message} :: {fields}",
+      color_mode=ColorMode::Always,
+      color_support=ColorSupport::Basic,
+      style_markup=StyleMarkupMode::Builtin,
+      target_style_markup=StyleMarkupMode::Builtin,
+      fields_style_markup=StyleMarkupMode::Disabled,
+      style_tags={
+        "accent": text_style(fg=Some("#4cc9f0"), bold=true),
+      },
+    ),
+  )
+  let formatter_obj = formatter_json.as_object().unwrap()
+  let style_tags_obj = formatter_obj.get("style_tags").unwrap().as_object().unwrap()
+  let accent_obj = style_tags_obj.get("accent").unwrap().as_object().unwrap()
+  inspect(formatter_obj.get("show_timestamp").unwrap().as_bool().unwrap(), content="false")
+  inspect(formatter_obj.get("show_target").unwrap().as_bool().unwrap(), content="false")
+  inspect(formatter_obj.get("separator").unwrap().as_string().unwrap(), content=" | ")
+  inspect(formatter_obj.get("field_separator").unwrap().as_string().unwrap(), content=",")
+  inspect(formatter_obj.get("template").unwrap().as_string().unwrap(), content="[{level}] {message} :: {fields}")
+  inspect(formatter_obj.get("color_mode").unwrap().as_string().unwrap(), content="always")
+  inspect(formatter_obj.get("color_support").unwrap().as_string().unwrap(), content="basic")
+  inspect(formatter_obj.get("style_markup").unwrap().as_string().unwrap(), content="builtin")
+  inspect(formatter_obj.get("target_style_markup").unwrap().as_string().unwrap(), content="builtin")
+  inspect(formatter_obj.get("fields_style_markup").unwrap().as_string().unwrap(), content="disabled")
+  inspect(accent_obj.get("bold").unwrap().as_bool().unwrap(), content="true")
+  inspect(accent_obj.get("fg").unwrap().as_string().unwrap(), content="#4cc9f0")
+
+  let sink_json = sink_config_to_json(
+    SinkConfig::new(
+      kind=SinkKind::File,
+      path="demo.log",
+      append=false,
+      auto_flush=false,
+      rotation=Some(file_rotation(128, max_backups=2)),
+      text_formatter=TextFormatterConfig::new(show_timestamp=false, color_mode=ColorMode::Auto),
+    ),
+  )
+  let sink_obj = sink_json.as_object().unwrap()
+  let sink_formatter_obj = sink_obj.get("text_formatter").unwrap().as_object().unwrap()
+  let rotation_obj = sink_obj.get("rotation").unwrap().as_object().unwrap()
+  inspect(sink_obj.get("kind").unwrap().as_string().unwrap(), content="file")
+  inspect(sink_obj.get("path").unwrap().as_string().unwrap(), content="demo.log")
+  inspect(sink_obj.get("append").unwrap().as_bool().unwrap(), content="false")
+  inspect(sink_obj.get("auto_flush").unwrap().as_bool().unwrap(), content="false")
+  inspect(sink_formatter_obj.get("show_timestamp").unwrap().as_bool().unwrap(), content="false")
+  inspect(sink_formatter_obj.get("color_mode").unwrap().as_string().unwrap(), content="auto")
+  inspect(rotation_obj.get("max_bytes").unwrap().as_number().unwrap().to_int(), content="128")
+  inspect(rotation_obj.get("max_backups").unwrap().as_number().unwrap().to_int(), content="2")
+
+  let logger_json = logger_config_to_json(
+    LoggerConfig::new(
+      min_level=Level::Warn,
+      target="api",
+      timestamp=true,
+      sink=SinkConfig::new(kind=SinkKind::TextConsole),
+      queue=Some(QueueConfig::new(8, overflow=QueueOverflowPolicy::DropNewest)),
+    ),
+  )
+  let logger_obj = logger_json.as_object().unwrap()
+  let logger_sink_obj = logger_obj.get("sink").unwrap().as_object().unwrap()
+  let logger_queue_obj = logger_obj.get("queue").unwrap().as_object().unwrap()
+  inspect(logger_obj.get("min_level").unwrap().as_string().unwrap(), content="WARN")
+  inspect(logger_obj.get("target").unwrap().as_string().unwrap(), content="api")
+  inspect(logger_obj.get("timestamp").unwrap().as_bool().unwrap(), content="true")
+  inspect(logger_sink_obj.get("kind").unwrap().as_string().unwrap(), content="text_console")
+  inspect(logger_queue_obj.get("max_pending").unwrap().as_number().unwrap().to_int(), content="8")
+  inspect(logger_queue_obj.get("overflow").unwrap().as_string().unwrap(), content="DropNewest")
+}
+
 test "default config helpers expose baseline config shapes" {
   let formatter = default_text_formatter_config()
   inspect(formatter.show_timestamp, content="true")