Summary

When configuring the Supabase MCP server in Copilot for Xcode, the MCP client sends a payload containing an unexpected prompt field. Supabase’s MCP server uses strict Zod validation and returns:

{"message": ": Unrecognized key(s) in object: 'prompt'"}

This makes the Supabase MCP unusable in Copilot for Xcode, even though it works in other MCP-compatible clients (Cursor, Claude Desktop, VS Code Copilot).

Repro Steps

1. Add Supabase MCP to the Copilot for Xcode mcp.json:

{
  "servers": {
    "supabase": {
      "type": "http",
      "url": "https://mcp.supabase.com/mcp"
    }
  }
}

2. Restart Copilot for Xcode.
3. Complete the OAuth browser login (this part works).
4. Try invoking any Supabase MCP tool.

Result:
The MCP server responds with:

{"message": ": Unrecognized key(s) in object: 'prompt'"}

Expected Behavior

Copilot for Xcode should only send fields defined in the MCP tool’s schema. Other MCP clients (Cursor, Claude Desktop, VS Code Copilot) do not send a prompt field and work correctly with Supabase MCP.

Actual Behavior

Copilot for Xcode appears to send a tool invocation payload similar to:

{
  "query": "example",
  "prompt": "extra value"
}

Supabase MCP tool schemas are strict (z.object(...).strict()), so any unknown key causes an error.

Why this is a Copilot for Xcode issue

• The Supabase MCP specification does not include prompt in any tool definition.
• Other MCP clients do not include this field.
• Only Copilot for Xcode adds this additional argument, causing schema validation to fail.

Suggested Fix

When invoking MCP tools:

• Do not inject a prompt field unless it is declared in the tool schema.
• MCP requests should match exactly the schema returned in the server’s tools metadata.

Environment

• Copilot for Xcode version: 0.45.0
• macOS version: 26.2 Beta (25C5031i)
• MCP server: https://mcp.supabase.com/mcp
• MCP type: HTTP with OAuth

Impact

This prevents the Supabase MCP from working in Copilot for Xcode, reducing MCP interoperability.