> ## Documentation Index
> Fetch the complete documentation index at: https://fentaris.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Transports

> Connect MCP servers using Fentaris transports.

> Connect upstream MCP servers with high-level transport helpers

This page is kept for older links. The current concepts entrypoint is [Servers and transports](/concepts/servers-and-transports).

## Quick Start

Use `stdio(...)` for local upstream MCP servers:

```ts theme={null} theme={"theme":{"light":"github-light","dark":"github-dark"}}
import { fentaris, mcp, stdio } from "@fentaris/core";

const proxy = fentaris({
  servers: [
    mcp("filesystem", {
      transport: stdio({
        command: "npx",
        args: ["-y", "@modelcontextprotocol/server-filesystem", "./demo-files"],
        stderr: "inherit",
      }),
    }),
  ],
});
```

Use `streamableHttp(...)` for native remote MCP HTTP endpoints:

```ts theme={null} theme={"theme":{"light":"github-light","dark":"github-dark"}}
import { fentaris, mcp, streamableHttp } from "@fentaris/core";

const proxy = fentaris({
  servers: [
    mcp("remote", {
      transport: streamableHttp({
        url: "https://mcp.example.com/mcp",
        auth: {
          headers: { "x-tenant": "acme" },
          bearerToken: "service-token",
        },
      }),
    }),
  ],
});
```

## Transport Matrix

| Direction  | Helper                | Use case                                                                    |
| ---------- | --------------------- | --------------------------------------------------------------------------- |
| Upstream   | `stdio(...)`          | Local MCP process over stdin/stdout.                                        |
| Upstream   | `streamableHttp(...)` | Remote native MCP Streamable HTTP endpoint.                                 |
| Upstream   | `SseMcpTransport`     | Legacy SSE-capable MCP servers.                                             |
| Upstream   | `HttpTransport`       | Compatibility adapter for REST-like `/listTools` and `/callTool` endpoints. |
| Downstream | `proxy.start()`       | Default Streamable HTTP exposure for MCP clients.                           |

## Stdio Options

### `command`

Executable to spawn.

### `args`

Arguments passed to the upstream process.

### `env`

Environment variables passed to the upstream process.

### `stderr`

How to handle stderr from the upstream process. Use `inherit` during local development to see upstream logs.

## HTTP-Family Auth

`streamableHttp(...)` supports static headers, bearer tokens, API keys, and per-user header resolvers.

```ts theme={null} theme={"theme":{"light":"github-light","dark":"github-dark"}}
streamableHttp({
  url: "https://mcp.example.com/mcp",
  auth: {
    resolveHeaders: ({ user }) => ({
      "x-user-id": user.id ?? "anonymous",
      authorization: `Bearer ${user.tokens?.remote ?? ""}`,
    }),
  },
})
```

<Note>
  Fentaris does not acquire or refresh OAuth tokens. Pass an already-valid access token through a resolver when the upstream needs one.
</Note>

## Close Cleanly

Close the proxy on shutdown so upstream transports can release processes, sockets, and sessions.

```ts theme={null} theme={"theme":{"light":"github-light","dark":"github-dark"}}
process.on("SIGTERM", async () => {
  await proxy.close();
  process.exit(0);
});
```

## Low-Level API

Transport classes such as `StdioTransport`, `StreamableHttpMcpTransport`, `SseMcpTransport`, and exposure transports remain available for advanced integrations. New application docs should prefer `stdio(...)`, `streamableHttp(...)`, and `proxy.start()`.

## Related Documentation

* [Servers and transports](/concepts/servers-and-transports)
* [Stdio transport](/reference/stdio-transport)
* [Proxy setup](/guides/proxy-setup)