Claude MCP server — connection failed, tools not available

// macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
// Windows: %APPDATA%\Claude\claude_desktop_config.json
{
  "mcpServers": {
    "my-postgres": {
      "command": "/opt/homebrew/bin/uvx",   // ABSOLUTE path — critical
      "args": ["mcp-server-postgres", "--connection-string", "postgres://..."],
      "env": {
        "PGSSLMODE": "require",
        "PATH": "/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin"
      }
    },

    "custom-tools": {
      "command": "/Users/me/.venv/bin/python",   // venv Python
      "args": ["/Users/me/tools/my_server.py"],
      "env": {
        "MY_API_KEY": "sk-...",
        "PYTHONUNBUFFERED": "1"                 // helps with log flushing
      }
    },

    "remote-service": {
      "url": "https://mcp.example.com/sse",
      "type": "sse"
    }
  }
}

# Diagnose why the command is not found

# 1) What is on PATH inside Claude Desktop?
#    Add this to your MCP config temporarily:
#      {"command": "/bin/sh", "args": ["-c", "echo PATH=$PATH >&2; exit 1"]}
#    Then check Claude Desktop's MCP log:
#      ~/Library/Logs/Claude/mcp*.log

# 2) Find the real path of the missing command
which uvx
# /opt/homebrew/bin/uvx  <- use this exact path

# 3) Test the server manually before wiring Claude
/opt/homebrew/bin/uvx mcp-server-postgres --help

# 1) Client-side logs (Claude Desktop)
tail -f ~/Library/Logs/Claude/mcp.log
tail -f ~/Library/Logs/Claude/mcp-server-my-postgres.log   # per-server log

# On Linux: ~/.config/Claude/logs/
# On Windows: %APPDATA%\Claude\logs\

# 2) Test the server directly with the MCP Inspector
# The Inspector is a browser UI that speaks MCP; use it to confirm the server works
npx @modelcontextprotocol/inspector /opt/homebrew/bin/uvx mcp-server-postgres

# Opens a UI at http://localhost:5173 where you can:
#   - see the tool list the server advertises
#   - call each tool with test inputs
#   - watch the JSON-RPC traffic

# 3) For SSE servers, curl the endpoint to confirm it is reachable
curl -N -H "Accept: text/event-stream" https://mcp.example.com/sse

# 4) For stdio servers, send a manual initialise message
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"debug","version":"1.0"}}}' \
  | /opt/homebrew/bin/uvx mcp-server-postgres

"""Minimal MCP-over-SSE server with session lifecycle awareness.

Uses fastapi + mcp SDK. Verify current SDK API in Anthropic MCP docs.
"""
from mcp.server import Server
from mcp.server.sse import SseServerTransport
from mcp.server.models import InitializationOptions, NotificationOptions
from fastapi import FastAPI, Request
from starlette.responses import Response
import mcp.types as types

app = FastAPI()
mcp_server = Server("my-service")

@mcp_server.list_tools()
async def list_tools():
    return [types.Tool(
        name="ping", description="Health check",
        inputSchema={"type": "object", "properties": {}, "required": []},
    )]

@mcp_server.call_tool()
async def call_tool(name: str, arguments: dict):
    if name == "ping":
        return [types.TextContent(type="text", text="pong")]
    raise ValueError(f"Unknown tool: {name}")

# SSE transport
transport = SseServerTransport("/messages")

@app.get("/sse")
async def handle_sse(request: Request):
    async with transport.connect_sse(request.scope, request.receive, request._send) as streams:
        await mcp_server.run(
            streams[0], streams[1],
            InitializationOptions(
                server_name="my-service", server_version="1.0.0",
                capabilities=mcp_server.get_capabilities(
                    notification_options=NotificationOptions(),
                    experimental_capabilities={},
                ),
            ),
        )
    # Return an empty response — SSE stream is done
    return Response(status_code=200)

@app.post("/messages/{session_id}")
async def handle_messages(session_id: str, request: Request):
    await transport.handle_post_message(session_id, request.scope,
                                       request.receive, request._send)
    return Response(status_code=200)

# Keep-alive: send a heartbeat every 15 seconds to prevent proxy timeouts
# (Add this to your mcp_server.run loop via a background task)