reflex-dev/reflex · error · ValueError

Output includes {value!s} which will be displayed as a strin

Error message

Output includes {value!s} which will be displayed as a string. If you are calling `str` on a Var, consider using .to_string() instead.

What it means

rx.el bare rendering validates that dynamic output is not a raw Var being coerced through str(), which would serialize a Var object instead of its runtime value. In RAISE performance mode this validation raises ValueError; in WARN mode it logs the same message.

Source

Thrown at packages/reflex-components-core/src/reflex_components_core/base/bare.py:49

def validate_str(value: str):
    """Validate a string value.

    Args:
        value: The value to validate.

    Raises:
        ValueError: If the value is a Var and the performance mode is set to raise.
    """
    perf_mode = get_performance_mode()
    if perf_mode != PerformanceMode.OFF and value.startswith("reflex___state"):
        if perf_mode == PerformanceMode.WARN:
            logger.warning(
                f"Output includes {value!s} which will be displayed as a string. If you are calling `str` on a Var, consider using .to_string() instead."
            )
        elif perf_mode == PerformanceMode.RAISE:
            msg = f"Output includes {value!s} which will be displayed as a string. If you are calling `str` on a Var, consider using .to_string() instead."
            raise ValueError(msg)


def _components_from_var(var: Var) -> Sequence[BaseComponent]:
    var_data = var._get_all_var_data()
    return var_data.components if var_data else ()


class Bare(Component):
    """A component with no tag."""

    contents: Var[Any]

    @classmethod
    def create(cls, contents: Any) -> Component:
        """Create a Bare component, with no tag.

        Args:
            contents: The contents of the component.

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Use Var operations: 'Count: ' + State.count.to_string()
2. Or use rx.cond / rx.foreach for dynamic fragments
3. Set perf_mode to PerformanceMode.WARN to downgrade to a warning if the coercion is intended

Example fix

// before
rx.el.div(f"Count: {State.count}")

// after
rx.el.div("Count: ", State.count.to_string())

# never interpolate Vars in f-strings inside rx.el children
children = ["Count: ", State.count.to_string()]

When it happens

Trigger: Calling rx.el(...)(f"{some_var}") or Bare.create with an f-string/format that str()s a Var while perf_mode is PerformanceMode.RAISE (default strict mode).

Common situations: Mixing f-strings with State Vars like f"Count: {State.count}" inside bare/rx.el output, instead of using Var concatenation or .to_string().

Related errors

• The component `{child_name}` can only be a child of the comp

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/8188bf7e76557277. Report an issue: GitHub.