home-assistant/core · error · HomeAssistantError

system_message_not_found

Error message

system_message_not_found

What it means

A HomeAssistantError with translation key 'system_message_not_found' raised when chat_log.content[0] is not a conversation.SystemContent instance. The Anthropic entity requires the first chat log item to be the system prompt, which it passes separately as the 'system' parameter of MessageCreateParamsStreaming.

Source

Thrown at homeassistant/components/anthropic/entity.py:946

        chat_log: conversation.ChatLog,
        structure_name: str | None = None,
        structure: vol.Schema | None = None,
    ) -> tuple[MessageCreateParamsStreaming, str | None]:
        """Get the model arguments."""
        options: dict[str, Any] = DEFAULT | self.subentry.data

        preloaded_tools = [
            "HassTurnOn",
            "HassTurnOff",
            "GetLiveContext",
            "code_execution",
            "web_search",
            "web_fetch",
        ]

        system = chat_log.content[0]
        if not isinstance(system, conversation.SystemContent):
            raise HomeAssistantError(
                translation_domain=DOMAIN, translation_key="system_message_not_found"
            )

        messages, container_id = _convert_content(chat_log.content[1:])

        model = options[CONF_CHAT_MODEL]

        model_args = MessageCreateParamsStreaming(
            model=model,
            messages=messages,
            max_tokens=options[CONF_MAX_TOKENS],
            system=system.content,
            stream=True,
            container=container_id,
        )

        if options[CONF_PROMPT_CACHING] == PromptCaching.PROMPT:
            model_args["system"] = [

View on GitHub (pinned to 58a3fdb3ea)

Solutions

  1. Ensure chat_log.async_add_content is first called with SystemContent (agent's instructions) before user turns
  2. Start a fresh conversation rather than resuming one whose stored history is missing the system block
  3. Update to the matching core version if the ChatLog construction API changed
Defensive patterns

Strategy: validation

Validate before calling

from homeassistant.components import conversation

def starts_with_system(chat_log: conversation.ChatLog) -> bool:
    return bool(chat_log.content) and isinstance(chat_log.content[0], conversation.SystemContent)

Try / catch

system = chat_log.content[0]
if not isinstance(system, conversation.SystemContent):
    raise HomeAssistantError(translation_domain=DOMAIN, translation_key="system_message_not_found")

Prevention

When it happens

Trigger: Invoking _async_handle_chat_log with a chat log whose first element is a user or assistant message — e.g. a caller built the ChatLog without async_add_content sequencing a system prompt first, or the system prompt was stripped.

Common situations: Custom scripts or integrations constructing a conversation.ChatLog manually and forgetting the system message; resuming a conversation_id whose stored history lacks the leading SystemContent.

Related errors

AI-assisted analysis of home-assistant/core@58a3fdb3ea (2026-08-14). Data as JSON: /api/errors/e68758aeb6ca00c9. Report an issue: GitHub.