HKUDS/Vibe-Trading · error · ValueError

HTTP MCP servers require an explicit type of 'sse' or…

Error message

HTTP MCP servers require an explicit type of 'sse' or 'streamableHttp'

What it means

Raised by MCPServerConfig.resolved_transport when a server definition has a url but no explicit type and no command/args/env. Because a url-based server could be either sse or streamableHttp, the schema refuses to guess and requires an explicit type field.

Solutions

  1. Add type: sse or type: streamableHttp to the server entry (streamableHttp is the modern default for HTTP MCP servers).
  2. If the server is actually a local process, replace url with command (and args/env).

Example fix

# before
mcp_servers:
  my-http:
    url: https://mcp.example.com/sse

# after
mcp_servers:
  my-http:
    type: sse
    url: https://mcp.example.com/sse
Defensive patterns

Strategy: validation

Validate before calling

def http_mcp_entry_valid(entry: dict) -> bool:
    if entry.get('url') and not (entry.get('command') or entry.get('args') or entry.get('env')):
        return entry.get('type') in ('sse', 'streamableHttp')
    return True

Type guard

def has_explicit_http_type(entry: dict) -> bool:
    return entry.get('type') in ('sse', 'streamableHttp')

Prevention

When it happens

Trigger: Configuring an MCP server entry with url set, type omitted, and no stdio fields; runtime config layering that strips the type while keeping the url.

Common situations: Migrating configs from older versions where url implied a transport; hand-written YAML entries copied from HTTP examples without the type key; overrides that accidentally clear type.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/6ee9a487da566792. Report an issue: GitHub.

Appendix: source

Thrown at agent/src/config/schema.py:370

    type: Literal["stdio", "sse", "streamableHttp"] | None = None
    command: str = ""
    args: list[str] = Field(default_factory=list)
    env: dict[str, str] = Field(default_factory=dict)
    url: str = ""
    headers: dict[str, str] = Field(default_factory=dict)
    auth: MCPOAuthConfig | None = None
    tool_timeout: float = Field(default=30.0, ge=0.1)
    init_timeout: float | None = Field(default=None, ge=0.1)
    enabled_tools: list[str] = Field(default_factory=lambda: ["*"])

    def resolved_transport(self) -> Literal["stdio", "sse", "streamableHttp"]:
        """Resolve the effective transport from explicit type or implied fields."""
        if self.type is not None:
            return self.type
        if self.command.strip() or self.args or self.env:
            return "stdio"
        if self.url.strip():
            raise ValueError("HTTP MCP servers require an explicit type of 'sse' or 'streamableHttp'")
        return "stdio"

    @model_validator(mode="after")
    def validate_transport_config(self) -> "MCPServerConfig":
        """Validate transport-specific MCP server configuration.

        Returns:
            The validated MCP server config instance.

        Raises:
            ValueError: If required fields are missing for the resolved
                transport or conflicting fields are provided.
        """
        transport = self.resolved_transport()

        if transport == "stdio":
            if not self.command.strip():
                raise ValueError("stdio MCP servers require a command")

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