reflex-dev/reflex · error · TypeError

`children` in `{fn.__name__}` must be annotated as `rx.Var[r

Error message

`children` in `{fn.__name__}` must be annotated as `rx.Var[rx.Component]`.

What it means

The reserved `children` parameter of an `@rx.memo` function must be annotated exactly as `rx.Var[rx.Component]` (a component pass-through slot). This error fires when `children` carries some other annotation that is not an event-handler annotation — such as `rx.Var[str]` or a bare type. It is raised at decoration time by `_analyze_params`.

Source

Thrown at packages/reflex-base/src/reflex_base/components/memo.py:1313

                annotation = Var[Any]
            else:
                annotation = Var[annotation]
            defaulted_params.append(parameter.name)
            if is_missing and missing_params is not None:
                missing_params.append(parameter.name)

        # Children parameters by name must match the children kind exactly —
        # otherwise we accept a value-typed `children` and emit confusing JSX.
        if (
            parameter.name == "children"
            and not _children_annotation_is_valid(annotation)
            and not _is_event_handler_annotation(annotation)[0]
        ):
            msg = (
                f"`children` in `{fn.__name__}` must be annotated as "
                "`rx.Var[rx.Component]`."
            )
            raise TypeError(msg)

        kind, kind_data = _classify_parameter(annotation, parameter.name, fn.__name__)
        spec = _SPECS[kind]
        spec.validate(parameter, fn.__name__, for_component)

        if kind is MemoParamKind.REST:
            rest_count += 1
            if rest_count > 1:
                msg = f"`@rx.memo` only supports one `rx.RestProp` in `{fn.__name__}`."
                raise TypeError(msg)

        js_prop_name = format.to_camel_case(parameter.name)
        placeholder_name = spec.placeholder_name(
            parameter.name, js_prop_name, for_component
        )

        params.append(
            MemoParam(

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Annotate `children` as `rx.Var[rx.Component]`
2. Rename the parameter to something like `text` or `content` if it is actually a string value, keeping `children` unclaimed

Example fix

# before
@rx.memo
def card(children: rx.Var[str]) -> rx.Component:
    return rx.card(children)

# after
@rx.memo
def card(children: rx.Var[rx.Component]) -> rx.Component:
    return rx.card(children)

import typing, reflex as rx

def check_children_is_component_var(fn) -> None:
    ch = typing.get_type_hints(fn).get("children")
    if ch is None:
        return
    if typing.get_origin(ch) is rx.Var and rx.Component in typing.get_args(ch):
        return
    raise TypeError("children must be annotated rx.Var[rx.Component]")

import typing, reflex as rx

def is_component_var(ann) -> bool:
    return typing.get_origin(ann) is rx.Var and rx.Component in typing.get_args(ann)

When it happens

Trigger: Declaring `def my_memo(children: rx.Var[str]) -> rx.Component` or `children: str` — the name matches the reserved slot but the annotation is neither `Var[Component]` nor an EventHandler (which `_validate_event_trigger` rejects separately).

Common situations: Naming a text/content string parameter `children` out of HTML habit; refactoring a component whose content prop was a string; generated code that reuses the name for a different type.

Related errors

• `rx.Var[rx.Component]` parameters in `{fn_name}` must be nam
• `children` in `{fn_name}` cannot be `rx.RestProp`.
• `children` in `{fn_name}` cannot be an `rx.EventHandler`; us
• All parameters of `{fn.__name__}` must be annotated as `rx.V
• Var-returning `@rx.memo` `{func_name}` cannot depend on embe

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/66797c761507a068. Report an issue: GitHub.