streamlit/streamlit · error · RuntimeError

server.trustedUserHeaders had multiple mappings for user key

Error message

server.trustedUserHeaders had multiple mappings for user key(s) {bad_keys}

What it means

Error "server.trustedUserHeaders had multiple mappings for user key(s) {bad_keys}" thrown in streamlit/streamlit.

Source

Thrown at lib/streamlit/config.py:3203

                where_defined=trusted_user_headers.where_defined,
            )
        except json.JSONDecodeError as jde:
            raise RuntimeError(
                f"bad JSON value for server.trustedUserHeaders: {jde.msg}"
            )

    # Fetch the latest value, since we might've updated it from JSON.
    final_config_value = options["server.trustedUserHeaders"].value
    # Ensure no user keys are duplicated.
    values = set()
    bad_keys = []
    for user_key in final_config_value.values():
        if user_key in values:
            bad_keys.append(user_key)
        values.add(user_key)

    if bad_keys:
        raise RuntimeError(
            f"server.trustedUserHeaders had multiple mappings for user key(s) {bad_keys}"
        )


_RESERVED_METRICS_USER_ATTRIBUTES: Final = frozenset({"type"})
# Valid OpenMetrics label name: ASCII letter/underscore followed by letters,
# digits, or underscores. Attribute names become metric label names, so an
# invalid name would emit malformed metrics.
_METRICS_LABEL_NAME_RE: Final = re.compile(r"^[a-zA-Z_][a-zA-Z0-9_]*$")


def _check_metrics_user_attributes() -> None:
    """Validate server.unsafeMetricsUserAttributes at config-load time.

    Rejects non-string entries, the reserved label name ``type`` (the event-type
    discriminator on the user_session_events family, which a user attribute must
    not shadow) and any name that is not a valid OpenMetrics label name (which
    would otherwise produce malformed metrics on the endpoint).

View on GitHub (pinned to 202661fc55)

When it happens

Trigger: Thrown at lib/streamlit/config.py:3203 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of streamlit/streamlit@202661fc55 (2026-08-26). Data as JSON: /api/errors/a7f7a6c32a71d705. Report an issue: GitHub.