fix(core): raise OutputParserException for non-dict JSON outputs

libs/core/langchain_core/utils/json.py

@@ -187,6 +187,11 @@ def parse_and_check_json_markdown(text: str, expected_keys: list[str]) -> dict:
     except json.JSONDecodeError as e:
         msg = f"Got invalid JSON object. Error: {e}"
         raise OutputParserException(msg) from e
+    if not isinstance(json_obj, dict):
+        raise OutputParserException(
+            f"Expected JSON object (dict), but got: {type(json_obj).__name__}. Raw content: {json_obj}",
+            llm_output=text
+        )
     for key in expected_keys:
         if key not in json_obj:
             msg = (

libs/core/tests/unit_tests/output_parsers/test_json.py

@@ -5,7 +5,10 @@
 import pytest
 from pydantic import BaseModel, Field
 
-from langchain_core.exceptions import OutputParserException
+from langchain.output_parsers.json import parse_and_check_json_markdown
+from langchain.schema import OutputParserException
+
+
 from langchain_core.output_parsers.json import (
     SimpleJsonOutputParser,
 )
@@ -210,6 +213,13 @@ def test_parse_json_with_code_blocks_and_newlines() -> None:
         "action_input": '```bar\n<div id="1" class="value">\n\ttext\n</div>```',
     }
 
+def test_parse_non_dict_json_output():
+    text = "```json\n1\n```"
+    with pytest.raises(OutputParserException) as exc_info:
+        parse_and_check_json_markdown(text, expected_keys=["foo"])
+
+    assert "Expected JSON object (dict)" in str(exc_info.value)
+
 
 TEST_CASES_ESCAPED_QUOTES = [
     JSON_WITH_ESCAPED_DOUBLE_QUOTES_IN_NESTED_JSON,