PrefectHQ/fastmcp · warning · RuntimeError

logging/setLevel is not available on MCP 2026-07-28 connecti

Error message

logging/setLevel is not available on MCP 2026-07-28 connections; the method requires per-session server state that the modern protocol does not have. Filter incoming log messages by level in your log_handler instead.

What it means

`logging/setLevel` exists in legacy MCP but is absent in the modern (MCP 2026-07-28) era, which has no per-session server state. FastMCP raises this RuntimeError from `client.set_logging_level()` when the connection's protocol version is modern and recommends filtering log messages client-side in your `log_handler`. Log notifications themselves still arrive.

Source

Thrown at fastmcp_slim/fastmcp/client/client.py:1414

        """Send a progress notification."""
        # Deprecated upstream in SDK v2 but deliberately kept per compat directive;
        # removed with the multi-round-trip follow-up.
        await self.session.send_progress_notification(  # ty: ignore[deprecated]
            progress_token, progress, total, message
        )

    async def set_logging_level(self, level: mcp_types.LoggingLevel) -> None:
        """Send a logging/setLevel request.

        Handshake-era servers only. `logging/setLevel` asks the server to
        remember a level for the rest of the session, and the 2026-07-28
        protocol has no session to remember it in — the method is absent from
        that era's registry. Log *notifications* are unaffected: they ride the
        request's own stream, so a server's `ctx.info()` still reaches you.
        Filter by level on the receiving side instead, in your `log_handler`.
        """
        if self.protocol_version in MODERN_PROTOCOL_VERSIONS:
            raise RuntimeError(
                "logging/setLevel is not available on MCP 2026-07-28 "
                "connections; the method requires per-session server state that "
                "the modern protocol does not have. Filter incoming log "
                "messages by level in your log_handler instead."
            )
        # Deprecated upstream in SDK v2 but deliberately kept per compat directive;
        # removed with the multi-round-trip follow-up.
        await self._await_with_session_monitoring(
            self.session.set_logging_level(level)  # ty: ignore[deprecated]
        )

    async def send_roots_list_changed(self) -> None:
        """Send a roots/list_changed notification."""
        # Deprecated upstream in SDK v2 but deliberately kept per compat directive;
        # removed with the multi-round-trip follow-up.
        await self.session.send_roots_list_changed()  # ty: ignore[deprecated]

    # --- Completion ---

View on GitHub (pinned to 1f02114297)

Solutions

1. Remove the set_logging_level call and filter by level inside your log_handler
2. Connect with mode='legacy' if you control the client and need server-side level state
3. Wrap in try/except RuntimeError and fall back to client-side filtering

Example fix

// before
await client.set_logging_level("debug")

// after
async def log_handler(msg) -> None:
    if msg.level in ("debug", "info"):
        print(msg.data)
# pass log_handler=log_handler when constructing the Client

def can_set_logging_level(client) -> bool:
    return client.protocol_version not in MODERN_PROTOCOL_VERSIONS

try:
    await client.set_logging_level("debug")
except RuntimeError as e:
    if "logging/setLevel is not available" in str(e):
        pass  # rely on log_handler level filtering instead
    else:
        raise

When it happens

Trigger: Calling `client.set_logging_level(...)` (or a session-level variant) on a client connected in modern mode / with a modern protocol version.

Common situations: Migrating client code from legacy to modern-era servers; shared logging helpers calling set_logging_level unconditionally; wanting dynamic verbosity control after a server protocol upgrade.

Related errors

• The client negotiated a modern protocol era (server/discover
• INVALID_PARAMS
• Unexpected elicitation action: {result.action}
• Error reading resource {uri!r}
• Error reading resource {uri!r}: {e}

AI-assisted analysis of PrefectHQ/fastmcp@1f02114297 (2026-08-29). Data as JSON: /api/errors/05895eb2193a714f. Report an issue: GitHub.