The mcp-proxy is a versatile proxy that lets MCP clients and servers communicate across different transport layers. It supports two modes: stdio to SSE/StreamableHTTP, where it runs as a proxy from a local stdio-based MCP server to a remote SSE endpoint, enabling clients (for example Claude Desktop) to talk to servers that are not natively SSE-enabled; and SSE to stdio, where it opens an SSE endpoint locally and spawns a stdio MCP server to handle requests from remote clients. Client mode accepts the MCP server SSE endpoint as the first argument and supports headers and OAuth2-based authentication (client id/secret and token URL) or a token supplied via API_ACCESS_TOKEN. The transport can be forced to streamable HTTP with --transport. The SSE-server mode exposes a port/host, passes environment variables to the local stdio server, and supports CORS configuration via --allow-origin; a --stateless option is available for streamable transports. Named servers can be defined via CLI or a JSON config file and are exposed under /servers/<name>/, with a global /status endpoint. A complete example config and usage patterns are provided in the README.