{"record":{"id":"ed895d2b1800d680","repo":"BerriAI/litellm","slug":"messages-must-be-a-list-ed895d","errorCode":null,"errorMessage":"messages must be a list","messagePattern":"messages must be a list","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"litellm/llms/bedrock/count_tokens/transformation.py","lineNumber":267,"sourceCode":"        Args:\n            request_data: The request payload\n\n        Raises:\n            ValueError: If the request is invalid\n        \"\"\"\n        if not request_data.get(\"model\"):\n            raise ValueError(\"model parameter is required\")\n\n        input_type: Final = self._detect_input_type(request_data)\n\n        if input_type == \"converse\":\n            # Validate Converse format (messages-based)\n            messages: Final = request_data.get(\"messages\", [])\n            if not messages:\n                raise ValueError(\"messages parameter is required for Converse input\")\n\n            if not isinstance(messages, list):\n                raise ValueError(\"messages must be a list\")\n\n            for i, message in enumerate(messages):\n                if not isinstance(message, dict):\n                    raise ValueError(f\"Message {i} must be a dictionary\")\n\n                if \"role\" not in message:\n                    raise ValueError(f\"Message {i} must have a 'role' field\")\n\n                if \"content\" not in message:\n                    raise ValueError(f\"Message {i} must have a 'content' field\")\n        else:\n            # For InvokeModel format, we need at least some content to count tokens\n            # The content structure varies by model, so we do minimal validation\n            if len(request_data) <= 1:  # Only has 'model' field\n                raise ValueError(\"Request must contain content to count tokens\")\n","sourceCodeStart":249,"sourceCodeEnd":283,"githubUrl":"https://github.com/BerriAI/litellm/blob/6c2dcb801bf2b75c18f1bb24140e7cf57465cc4d/litellm/llms/bedrock/count_tokens/transformation.py#L249-L283","documentation":"Type check inside Converse-format validation: 'messages' must be a Python list. Passing a single message dict, a string, or any other type raises ValueError with this message.","triggerScenarios":"Calling count tokens with messages being a single message object ({'role':...}) instead of a list of messages, or with a JSON-decoded payload where messages was serialized as something else.","commonSituations":"SDK wrappers that accept one message for convenience, or deserialization bugs that wrap/unwrap the array incorrectly.","solutions":["Wrap a single message in a list: messages=[msg] not messages=msg","Add an assertion before the call: assert isinstance(req['messages'], list)"],"exampleFix":"# before\nreq = {'model': model, 'messages': {'role': 'user', 'content': [...]}}\n\n# after\nreq = {'model': model, 'messages': [{'role': 'user', 'content': [...]}]}","handlingStrategy":"type-guard","validationCode":"if not isinstance(req.get(\"messages\"), list):\n    raise TypeError(\"messages must be a list of message dicts\")","typeGuard":"def is_message_list(v) -> bool:\n    return isinstance(v, list) and all(isinstance(m, dict) for m in v)","tryCatchPattern":null,"preventionTips":["Type payloads with TypedDict/Pydantic models so shape errors surface at parse time","Wrap single-message convenience APIs at your boundary: msg if list else [msg]"],"tags":["bedrock","count-tokens","validation","types"],"backgroundTag":null,"analyzedSha":"6c2dcb801bf2b75c18f1bb24140e7cf57465cc4d","analyzedAt":"2026-08-15T07:12:03.035Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}