langchain-ai/deepagents · error · TypeError

--model-params must be a JSON object, got {type}

Error message

--model-params must be a JSON object, got {type}

What it means

After successful JSON parsing, `_extract_model_params_flag` checks the result is a dict. JSON allows top-level arrays, strings, numbers, booleans, and null; `--model-params` only accepts an object of model kwargs, so anything else raises this TypeError naming the actual parsed type.

Source

Thrown at libs/code/deepagents_code/app.py:1989

        rest = after[end + 1 :].lstrip()
    else:
        # Non-brace, non-quoted — take the next whitespace-delimited token.
        parts = after.split(None, 1)
        json_str = parts[0]
        rest = parts[1] if len(parts) > 1 else ""

    remaining = f"{before} {rest}".strip()
    try:
        params = json.loads(json_str)
    except json.JSONDecodeError:
        msg = (
            f"Invalid JSON in --model-params: {json_str!r}. "
            'Expected format: --model-params \'{"key": "value"}\''
        )
        raise ValueError(msg) from None
    if not isinstance(params, dict):
        msg = "--model-params must be a JSON object, got " + type(params).__name__
        raise TypeError(msg)
    return remaining, params


def _format_model_params(extra_kwargs: dict[str, Any] | None) -> str:
    """Render `--model-params` as a stable, key-sorted JSON suffix.

    Args:
        extra_kwargs: The parsed `--model-params` payload, or `None`.

    Returns:
        ` with model params {json}` when `extra_kwargs` is non-empty;
        otherwise an empty string so callers can unconditionally concatenate.
    """
    if not extra_kwargs:
        return ""
    return f" with model params {json.dumps(extra_kwargs, sort_keys=True)}"

View on GitHub (pinned to a1af029e6e)

Solutions

1. Wrap the value in a JSON object with the kwarg as key: --model-params '{"temperature": 0.5}'
2. Check the value parses to an object: python -c "import json;d=json.loads('<v>');assert isinstance(d,dict)"
3. For list-shaped settings, nest them under a key inside the object

Example fix

// before
--model-params '["temperature", 0.5]'
// after
--model-params '{"temperature": 0.5}'

parsed = json.loads(value)
if not isinstance(parsed, dict):
    raise TypeError(f"--model-params needs a JSON object, got {type(parsed).__name__}")

def is_model_params_object(value: str) -> bool:
    try:
        return isinstance(json.loads(value), dict)
    except json.JSONDecodeError:
        return False

try:
    remaining, params = _extract_model_params_flag(argv)
except TypeError as exc:
    print(exc)  # names the parsed type
    sys.exit(2)

When it happens

Trigger: Passing a valid-JSON-but-not-object value: `--model-params '[1,2]'`, `--model-params '"hello"'`, `--model-params '42'`, `--model-params 'null'`, or `--model-params 'true'`.

Common situations: Users intending a list of parameters, or passing a scalar value (a temperature number alone) expecting it to be treated as a setting.

Related errors

• Invalid JSON in --model-params: {json_str!r}. Expected forma
• --max-content must be positive
• --list must be positive
• -32002
• dcode: {message}

AI-assisted analysis of langchain-ai/deepagents@a1af029e6e (2026-08-29). Data as JSON: /api/errors/c8e6d8802570a922. Report an issue: GitHub.