BerriAI/litellm · error · HTTPException

MCP upstream registration endpoint returned no response

Error message

MCP upstream registration endpoint returned no response

What it means

Defensive guard in the MCP dynamic-client-registration POST: httpx returned no response object for the registration request, so registration cannot be inspected or trusted and fails loudly instead of silently continuing.

Source

Thrown at litellm/proxy/_experimental/mcp_server/discoverable_endpoints.py:1453

    upstream rejection instead of a generic 500 and failing loud on an absent response."""
    headers: Final = {
        "Content-Type": "application/json",
        "Accept": "application/json",
    }
    async_client: Final = get_async_httpx_client(llm_provider=httpxSpecialProvider.Oauth2Register)
    try:
        response: Final = await async_client.post(
            registration_url,
            headers=headers,
            json=register_data,
        )
        if response is not None:
            response.raise_for_status()
    except httpx.HTTPStatusError as exc:
        status_code, detail = dcr_fault_detail(classify_upstream_dcr_rejection(exc.response, log_context=server_id))
        raise HTTPException(status_code=status_code, detail=detail) from exc
    if response is None:
        raise HTTPException(
            status_code=502,
            detail="MCP upstream registration endpoint returned no response",
        )
    return response


class EphemeralDcrClient(BaseModel):
    """A DCR client minted for a single authorize round trip and never stored by the gateway."""

    model_config = ConfigDict(frozen=True)
    client_id: str = Field(min_length=1)
    client_secret: str | None = None
    token_endpoint_auth_method: MCPTokenEndpointAuthMethod | None = None


_EPHEMERAL_DCR_CLIENT_CACHE: Final = InMemoryCache(default_ttl=_OAUTH_STATE_COOKIE_TTL_SECONDS)
_EPHEMERAL_DCR_MINT_LOCKS: Final[dict[str, asyncio.Lock]] = {}

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Check connectivity to the upstream registration endpoint.
2. Verify the registration endpoint URL and server availability.

Example fix

curl the registration endpoint to confirm it responds.

When it happens

Trigger: Thrown at litellm/proxy/_experimental/mcp_server/discoverable_endpoints.py:1453 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/12ae5fcecfa40006. Report an issue: GitHub.