reflex-dev/reflex · error · ValueError

Catchall pattern `{part}` is not valid. Only `{constants.Rou

Error message

Catchall pattern `{part}` is not valid. Only `{constants.RouteRegex.SPLAT_CATCHALL}` is allowed.

What it means

Reflex only supports one catchall pattern spelling: [[...slug]] (constants.RouteRegex.SPLAT_CATCHALL). Any other bracketed segment starting with '[[...' or '[...' (e.g. '[...args]', '[[...catch]]') is rejected by verify_route_validity when the page is added.

Source

Thrown at reflex/route.py:34

        route: The route that need to be checked

    Raises:
        ValueError: If the route is invalid.
    """
    route_parts = route.removeprefix("/").split("/")
    for i, part in enumerate(route_parts):
        if constants.RouteRegex.SLUG.fullmatch(part):
            continue
        if not part.startswith("[") or not part.endswith("]"):
            msg = (
                f"Route part `{part}` is not valid. Reflex only supports "
                "alphabetic characters, underscores, and hyphens in route parts. "
            )
            raise ValueError(msg)
        if part.startswith(("[[...", "[...")):
            if part != constants.RouteRegex.SPLAT_CATCHALL:
                msg = f"Catchall pattern `{part}` is not valid. Only `{constants.RouteRegex.SPLAT_CATCHALL}` is allowed."
                raise ValueError(msg)
            if i != len(route_parts) - 1:
                msg = f"Catchall pattern `{part}` must be at the end of the route."
                raise ValueError(msg)
            continue
        if part.startswith("[["):
            if constants.RouteRegex.OPTIONAL_ARG.fullmatch(part):
                continue
            msg = (
                f"Route part `{part}` with optional argument is not valid. "
                "Reflex only supports optional arguments that start with an alphabetic character or underscore, "
                "followed by alphanumeric characters or underscores."
            )
            raise ValueError(msg)
        if not constants.RouteRegex.ARG.fullmatch(part):
            msg = (
                f"Route part `{part}` with argument is not valid. "
                "Reflex only supports argument names that start with an alphabetic character or underscore, "
                "followed by alphanumeric characters or underscores."

View on GitHub (pinned to 45b8ed5ab7)

Solutions

Use exactly [[...slug]] as the catchall segment, e.g. route='/docs/[[...slug]]'
If you need a custom name, access the args via the default slug name in the page's state instead of renaming the route segment

Example fix

# before
app.add_page(docs, route='/docs/[...path]')

# after
app.add_page(docs, route='/docs/[[...slug]]')

Defensive patterns

Strategy: validation

Validate before calling

from reflex.utils.constants import RouteRegex

def is_valid_catchall(part: str) -> bool:
    return part == RouteRegex.SPLAT_CATCHALL.value if hasattr(RouteRegex.SPLAT_CATCHALL, 'value') else part == RouteRegex.SPLAT_CATCHALL.pattern

Type guard

def is_valid_route_part(part: str) -> bool:
    if part.startswith(('[[...', '[...')):
        return part == '[[...slug]]'
    return True

Try / catch

try:
    app.add_page(page, route=route)
except ValueError as e:
    print(f'bad route: {e}')

Prevention

Memorize the single allowed catchall spelling [[...slug]]
Add a test asserting all catchall routes equal [[...slug]]

When it happens

Trigger: app.add_page(catch, route='/docs/[...path]') or '/docs/[[...path]]'-variants that don't exactly equal '[[...slug]]', such as different arg names or single brackets.

Common situations: Coming from Next.js where any name like [...slug] or [...path] works; renaming the catchall arg to something meaningful like 'path' or 'rest'.

Related errors

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/3a2be83aec94cc13. Report an issue: GitHub.