reflex-dev/reflex · error · ValueError

Markdown component must have exactly one child containing th

Error message

Markdown component must have exactly one child containing the markdown source.

What it means

rx.markdown() requires exactly one child — the markdown source — as either a Python string or a Var. Zero children, multiple children, or a non-string child (like a component) produce ValueError because the component compiles the source into react-markdown at build time.

Source

Thrown at packages/reflex-components-markdown/src/reflex_components_markdown/markdown.py:247

        cls,
        *children,
        **props,
    ) -> Component:
        """Create a markdown component.

        Args:
            *children: The children of the component.
            **props: The properties of the component.

        Returns:
            The markdown component.

        Raises:
            ValueError: If the children are not valid.
        """
        if len(children) != 1 or not isinstance(children[0], (str, Var)):
            msg = "Markdown component must have exactly one child containing the markdown source."
            raise ValueError(msg)

        # Update the base component map with the custom component map.
        component_map = {**get_base_component_map(), **props.pop("component_map", {})}

        # Get the markdown source.
        src = children[0]

        # Dedent the source.
        if isinstance(src, str):
            src = textwrap.dedent(src)

        # Create the component.
        return super().create(
            src,
            component_map=component_map,
            component_map_hash=cls._component_map_hash(component_map),
            **props,
        )

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Pass exactly one string: rx.markdown('# Hello')
2. For dynamic content pass a single Var: rx.markdown(State.md_text)
3. Join multiple blocks into one string: rx.markdown('\n\n'.join(blocks))

Example fix

# before
rx.markdown('# Title', rx.text('body'))
# after
rx.markdown('# Title\n\nbody')

assert len(children) == 1 and isinstance(children[0], (str, Var))
rx.markdown(*children)

When it happens

Trigger: rx.markdown() with no args, rx.markdown('# Hi', rx.text('extra')), or rx.markdown(rx.text('# Hi')).

Common situations: Forgetting the source string; trying to nest components inside markdown; passing a list of blocks instead of one joined string.

Related errors

• f"No markdown component found for tag: {tag}."
• f"FormControl can only have at most one child, got {len(chil
• f"Expected EscapeSequence to have a single RawText child, go
• ChildrenTypeError(component=cls.__name__, child=child)
• Do not override _add_style directly. Use add_style instead.

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/4f9edbfd5ed1d294. Report an issue: GitHub.