tirth8205/code-review-graph · error · ValueError

unsupported transport: {transport!r}

Error message

unsupported transport: {transport!r}

What it means

Raised by main() when the requested MCP transport string is neither 'stdio' nor 'streamable-http'. The f-string echoes the offending value so typos and unsupported transports are immediately visible.

Source

Thrown at code_review_graph/main.py:1256

            mcp.run(transport="stdio", show_banner=False)
        elif transport == "streamable-http":
            if host is None or port is None:
                raise ValueError("streamable-http transport requires host and port")
            # Validate Host/Origin on the loopback HTTP endpoint. Without it a web
            # page the user visits can point a hostname it controls at 127.0.0.1
            # (DNS rebinding) and drive the tools, which read the user's code.
            # Non-browser MCP clients send no Origin and are unaffected; see
            # code_review_graph.http_origin_guard.
            from .http_origin_guard import build_http_middleware

            mcp.run(
                transport="streamable-http",
                host=host,
                port=port,
                middleware=build_http_middleware(host, port),
            )
        else:
            raise ValueError(f"unsupported transport: {transport!r}")
    finally:
        if watch_store is not None:
            watch_store.close()
        _incremental._MCP_STDIO_ACTIVE = previous_stdio_state


if __name__ == "__main__":
    main()

View on GitHub (pinned to b58668751a)

Solutions

1. Use 'stdio' for local clients or exactly 'streamable-http' for HTTP (note the hyphen, not 'streamable_http' or 'sse').
2. Check for trailing whitespace/case differences in the transport value.
3. If you need SSE/WebSockets, front the streamable-http endpoint with your own proxy instead.

Example fix

# before
mcp --transport sse
# after
mcp --transport streamable-http --host 127.0.0.1 --port 8080

VALID_TRANSPORTS = {"stdio", "streamable-http"}
if transport not in VALID_TRANSPORTS:
    raise SystemExit(f"transport must be one of {sorted(VALID_TRANSPORTS)}, got {transport!r}")

def is_supported_transport(value: str) -> bool:
    return value in {"stdio", "streamable-http"}

try:
    main()
except ValueError as exc:
    if str(exc).startswith("unsupported transport"):
        print(exc); sys.exit(2)

When it happens

Trigger: Passing a transport like 'sse', 'websocket', 'HTTP', or any misspelling to the MCP entrypoint — only exact 'stdio' and 'streamable-http' are accepted.

Common situations: Users coming from FastMCP docs that list 'sse' as a transport; case mismatches like 'Stdio'; config files with an old/renamed transport name after a version change.

Related errors

• streamable-http transport requires host and port

AI-assisted analysis of tirth8205/code-review-graph@b58668751a (2026-08-28). Data as JSON: /api/errors/861d2a36d3b816fb. Report an issue: GitHub.