[BUG] JetBrains Rider MCP server connects but registers zero tools

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The JetBrains Rider MCP server connects successfully to Claude Code — the server description appears in MCP instructions ("You can interact with a JetBrains IntelliJ IDE...") — but zero tools are registered. ToolSearch for "jetbrains" returns no deferred tools.

Direct curl queries to the same MCP endpoint successfully return all 41 tools via tools/list, proving the server is functioning correctly.

Tested all three transports with identical results (connects, shows description, zero tools):

1. STDIO proxy (Rider's auto-configured default via McpStdioRunnerKt)
2. SSE (http://127.0.0.1:64342/sse)
3. Streamable HTTP (http://127.0.0.1:64342/stream)

What Should Happen?

Claude Code should register and expose the 41 tools returned by the MCP server's tools/list response, making them available via ToolSearch and callable during conversations.

Error Messages/Logs

No error messages are shown. The server appears connected and healthy. ToolSearch simply returns "No matching deferred tools found".

Steps to Reproduce

1. Install Rider 2026.1 (Build #RD-261.22158.335)
2. Open a project in Rider
3. Ensure MCP Server is enabled in Settings → Tools → MCP Server (port 64342)
4. Use Rider's auto-configure to generate the Claude Code MCP config in ~/.claude/.mcp.json
5. Start Claude Code
6. The JetBrains server description appears in system context, confirming connection
7. Run ToolSearch for "jetbrains" — returns zero tools

To verify Rider is returning tools correctly:

# Initialize MCP session
curl -s -D - http://127.0.0.1:64342/stream \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}'
# Returns mcp-session-id header

# List tools using session ID from above
curl -s http://127.0.0.1:64342/stream \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "mcp-session-id: <session-id-from-above>" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'
# Returns 55KB response with 41 tools

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.88

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

The 41 tools Rider exposes include: execute_run_configuration, build_project, get_file_problems, find_files_by_glob, search_in_files_by_regex, rename_refactoring, execute_terminal_command, run_inspection_kts, execute_sql_query, and more.

MCP config used (STDIO proxy):

{
  "mcpServers": {
    "rider": {
      "type": "stdio",
      "command": "C:\\Users\\...\\Rider\\jbr\\bin\\java",
      "args": [
        "-classpath",
        "C:\\...\\mcpserver-frontend.jar;...",
        "com.intellij.mcpserver.stdio.McpStdioRunnerKt"
      ],
      "env": {
        "IJ_MCP_SERVER_PORT": "64342"
      }
    }
  }
}

Related JetBrains issue: RIDER-128984 (Rider MCP project-related tools return an empty list)