@sendmsg/mcp-client

stdio ↔ HTTPS bridge for sendmsg.io's Model Context Protocol server. Use this from Claude Desktop, Cursor, Windsurf, or any other MCP client that only speaks stdio while our server speaks Streamable HTTP at https://mcp.sendmsg.io/mcp.

Install

One-time global install (gives you the sendmsg-mcp command on your PATH). Requires Node.js 18+.

npm install -g @sendmsg/mcp-client
sendmsg-mcp --version

Re-run npm install -g @sendmsg/mcp-client later to upgrade.

Why not npx? It works on most setups but on some Node + shell combinations the temporary npx-installed .bin/ directory is not visible to the spawned subprocess, producing sh: sendmsg-mcp: command not found. The global install always works, and the resulting sendmsg-mcp command lives at a stable path that every MCP client can invoke.

Setup

1. Mint a Personal Access Token at https://console.sendmsg.io/mcp/personal-access-tokens.
2. Drop the snippet below into your MCP client config:

Claude Desktop

~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "sendmsg": {
      "command": "sendmsg-mcp",
      "env": {
        "SENDMSG_MCP_TOKEN": "pat_xxxxxxxx"
      }
    }
  }
}

Cursor

~/.cursor/mcp.json:

{
  "mcpServers": {
    "sendmsg": {
      "command": "sendmsg-mcp",
      "env": {
        "SENDMSG_MCP_TOKEN": "pat_xxxxxxxx"
      }
    }
  }
}

Windsurf

~/.windsurf/mcp_config.json — same shape as the Cursor config above.

Environment

| Variable | Required | Default | Notes | |---|---|---|---| | SENDMSG_MCP_TOKEN | yes | — | Personal Access Token from the console | | SENDMSG_MCP_URL | no | https://mcp.sendmsg.io/mcp | Override only for self-hosted / staging |

What it does

1. Reads newline-delimited JSON-RPC frames from stdin.
2. POSTs each frame to SENDMSG_MCP_URL with Authorization: Bearer <PAT>.
3. Forwards the response (whether application/json or text/event-stream) back to stdout as newline-delimited JSON.
4. Tracks the mcp-session-id header so subsequent requests join the same server-side session (FastMCP's StreamableHTTPSessionManager needs this).
5. Surfaces 401 / 403 with an actionable hint instead of just exiting.

Stderr is reserved for log messages; stdout is reserved for JSON-RPC frames so the upstream client can parse them.

Permissions

Your token inherits whatever your console account can do — exactly. A read_only user gets read scopes; a domain_admin is limited to their allowed_domains; a super_admin can do everything. Bottom line: the bridge cannot escalate; the MCP server enforces every check per call.

Troubleshooting

| Symptom | Cause / fix | |---|---| | 401 Unauthorized on first call | PAT invalid / revoked. Re-mint at https://console.sendmsg.io/account/mcp/tokens | | 403 Forbidden on send | Your account is in read_only mode or the recipient's domain is outside your allowed_domains | | network error talking to https://mcp.sendmsg.io/mcp | Check that the host is reachable: curl -i https://mcp.sendmsg.io/health | | Client hangs on first request | Some clients only flush one frame per stdin chunk — try restarting the MCP client |

License

MIT