FoundationAgents/OpenManus · warning · ValueError

Server URL is required.

Error message

Server URL is required.

What it means

Raised by MCPClient.connect_sse (app/tool/mcp.py:53) when server_url is empty/None. It is a pure input-validation guard executed before any AsyncExitStack or sse_client machinery is set up, so hitting it means no connection attempt was made and no cleanup is needed.

Source

Thrown at app/tool/mcp.py:53

class MCPClients(ToolCollection):
    """
    A collection of tools that connects to multiple MCP servers and manages available tools through the Model Context Protocol.
    """

    sessions: Dict[str, ClientSession] = {}
    exit_stacks: Dict[str, AsyncExitStack] = {}
    description: str = "MCP client tools for server interaction"

    def __init__(self):
        super().__init__()  # Initialize with empty tools list
        self.name = "mcp"  # Keep name for backward compatibility

    async def connect_sse(self, server_url: str, server_id: str = "") -> None:
        """Connect to an MCP server using SSE transport."""
        if not server_url:
            raise ValueError("Server URL is required.")

        server_id = server_id or server_url

        # Always ensure clean disconnection before new connection
        if server_id in self.sessions:
            await self.disconnect(server_id)

        exit_stack = AsyncExitStack()
        self.exit_stacks[server_id] = exit_stack

        streams_context = sse_client(url=server_url)
        streams = await exit_stack.enter_async_context(streams_context)
        session = await exit_stack.enter_async_context(ClientSession(*streams))
        self.sessions[server_id] = session

        await self._initialize_and_list_tools(server_id)

    async def connect_stdio(

View on GitHub (pinned to 52a13f2a57)

Solutions

1. Set the missing URL in config/env (e.g. export MCP_SSE_URL=http://host:port/sse) and confirm it is non-empty before calling.
2. Validate before connecting: `if not server_url: raise/fallback` in your bootstrap code with a clear config-path-naming message.
3. If the URL comes from a list of servers, skip/filter empty entries instead of passing them to connect_sse.

Example fix

// before
url = os.environ.get('MCP_SSE_URL', '')
await mcp.connect_sse(url)

// after
url = os.environ.get('MCP_SSE_URL')
if not url:
    raise RuntimeError('MCP_SSE_URL is not configured')
await mcp.connect_sse(url)

url = os.environ.get('MCP_SSE_URL')
if not url or not url.startswith(('http://', 'https://')):
    raise RuntimeError(f'MCP SSE URL misconfigured: {url!r}')
await mcp.connect_sse(url, server_id='my-server')

def is_sse_url(u: str | None) -> bool:
    return isinstance(u, str) and u.strip().startswith(('http://', 'https://'))

try:
    await mcp.connect_sse(url, server_id)
except ValueError as e:
    if 'Server URL is required' in str(e):
        fix_config_and_reload()
    else:
        raise

When it happens

Trigger: Calling `await mcp.connect_sse('')` or `await mcp.connect_sse(None)`; commonly the result of reading a server URL from config/env (e.g. MCP_SSE_URL unset) and passing it through without a default or check.

Common situations: Missing environment variable or empty config entry for the MCP server URL in deployment (env var not exported in the service unit/container); templating bugs producing empty strings; tests constructing the client without wiring a URL.

Related errors

• Server URL is required for SSE connection
• Command is required for stdio connection
• Unsupported connection type: {self.connection_type}
• Failed to load MCP server config: {e}
• Server command is required.

AI-assisted analysis of FoundationAgents/OpenManus@52a13f2a57 (2026-08-15). Data as JSON: /api/errors/21f34381be522e3b. Report an issue: GitHub.