reflex-dev/reflex · error · ValueError

f"No markdown component found for tag: {tag}."

Error message

f"No markdown component found for tag: {tag}."

What it means

When customizing rx.markdown(component_map={...}), the component_map must contain an entry for every markdown tag Reflex renders (h1, p, code, etc.). get_component looks up the component factory by tag and raises ValueError for unknown tags — including tags introduced in a base map you overrode or removed.

Source

Thrown at packages/reflex-components-markdown/src/reflex_components_markdown/markdown.py:362

        )

    def get_component(self, tag: str, **props) -> Component:
        """Get the component for a tag and props.

        Args:
            tag: The tag of the component.
            **props: The props of the component.

        Returns:
            The component.

        Raises:
            ValueError: If the tag is invalid.
        """
        # Check the tag is valid.
        if tag not in self.component_map:
            msg = f"No markdown component found for tag: {tag}."
            raise ValueError(msg)

        # If the children are set as a prop, don't pass them as children.
        children = [_CHILDREN] if props.get("children") is None else []
        # Get the component.
        return self.component_map[tag](*children, **props).set(special_props=[_PROPS])

    def format_component(self, tag: str, **props) -> str:
        """Format a component for rendering in the component map.

        Args:
            tag: The tag of the component.
            **props: Extra props to pass to the component function.

        Returns:
            The formatted component.
        """
        return str(self.get_component(tag, **props)).replace("\n", "")

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Merge your map over the base: component_map={**rx.markdown.default_component_map, 'h1': my_h1} (or extend the map returned by get_base_component_map rather than replacing it)
2. Check the exact tag string casing in your component_map keys
3. Upgrade reflex-components-markdown — new markdown tags in newer versions require an updated base map

Example fix

# before
rx.markdown(src, component_map={'h1': custom_h1})
# after
from reflex_components_markdown.markdown import get_base_component_map
rx.markdown(src, component_map={**get_base_component_map(), 'h1': custom_h1})

from reflex_components_markdown.markdown import get_base_component_map
merged = {**get_base_component_map(), **custom}
for tag in required_tags:
    assert tag in merged, f'missing tag {tag}'

When it happens

Trigger: Passing a component_map that replaces the base map without covering all standard tags, or referencing a tag string with different casing/typo in _get_tag_map customizations.

Common situations: Extending markdown styling by supplying only your custom tags instead of merging with the default map; overriding 'code' handling and breaking the lookup for nested tags like 'codeblock'.

Related errors

• Markdown component must have exactly one child containing th
• 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.
• The component `{comp_name}` cannot have `{child_name}` as a

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/90efa32765ef7b82. Report an issue: GitHub.