Seems to break Claude Code.

[SilverTab]

This MCP appears to work perfectly fine in Cursor for me, but as soon as I add it to Claude Code, every subsequent message fails with:

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.46.custom.name: String should have at most 64 characters"}}

Removing the MCP from my Claude config fixes the issue.

[cameroncooke]

Thanks for reporting. I've just tried it and I'm not seeing any issues

Can you provide the following:

1. Version of Claude Desktop
2. macOS version
3. Xcode version
4. Contents of ~/Library/Application Support/Claude/claude_desktop_config.json
5. MCP logs (tail -n 20 -F ~/Library/Logs/Claude/mcp*.log) see https://modelcontextprotocol.io/docs/tools/debugging#using-chrome-devtools

Thanks.

[SilverTab]

Sure thing!

1. Using latest version of claude: Version 0.9.2
2. macOS 14.6
3. Version 16.2
4. Content of my claude_desktop_config.json:

{
  "globalShortcut": "",
  "mcpServers": {
    "XcodeBuildMCP": {
      "command": "mise",
      "args": [
        "x",
        "npm:xcodebuildmcp@latest",
        "--",
        "xcodebuildmcp"
      ]
    }
  }
}

5. Content of mcp.log and mcp-server-XcodeBuildMCP.log seem to both be filled with:

2025-04-21T20:51:14.153Z [info] [XcodeBuildMCP] Message from server: {"jsonrpc":"2.0","id":26,"error":{"code":-32601,"message":"Method not found"}}
2025-04-21T20:51:14.153Z [info] [XcodeBuildMCP] Message from server: {"jsonrpc":"2.0","id":27,"error":{"code":-32601,"message":"Method not found"}}
2025-04-21T20:51:14.153Z [info] [XcodeBuildMCP] Message from client: {"method":"prompts/list","params":{},"jsonrpc":"2.0","id":28}
2025-04-21T20:51:14.154Z [info] [XcodeBuildMCP] Message from server: {"jsonrpc":"2.0","id":28,"error":{"code":-32601,"message":"Method not found"}}
2025-04-21T20:51:44.149Z [info] [XcodeBuildMCP] Message from client: {"method":"resources/list","params":{},"jsonrpc":"2.0","id":29}
2025-04-21T20:51:44.150Z [info] [XcodeBuildMCP] Message from client: {"method":"resources/list","params":{},"jsonrpc":"2.0","id":30}
2025-04-21T20:51:44.154Z [info] [XcodeBuildMCP] Message from server: {"jsonrpc":"2.0","id":29,"error":{"code":-32601,"message":"Method not found"}}
2025-04-21T20:51:44.154Z [info] [XcodeBuildMCP] Message from server: {"jsonrpc":"2.0","id":30,"error":{"code":-32601,"message":"Method not found"}}

[SilverTab]

fwiw, I tried both adding it to claude code via claude mcp add ... and via claude mcp add-from-claude-desktop
It looks like everything works just fine in Claude Desktop, and in Cursor. But in Claude Code, as soon as I configure the MCP, and then send any message (I have to send a message to get the error), I get:

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.46.custom.name: String should have at most 64 characters"}}

[cameroncooke]

I'm sorry, my mistake. I misinterpreted your issue to be with Claude Desktop. I've not tried it with Claude Code yet. Let me do some more digging.

[cameroncooke]

Do you have any other MCP servers configured with Claude Code? The reason I ask is that the error refers to tools.46.custom.name specifically tools.46, the current version of XcodeBuildMCP exposes only 39 tools.

It's not clear to me how Claude Code works, but it might be using one or more implicit MCP servers to provide core functionality.

[cameroncooke]

Just found this issue anthropics/claude-code#310 - which seems to be the same error potentially with a Terraform MCP server, which has been labelled as a bug.

[cameroncooke]

It might be worth posting an issue on https://github.com/anthropics/claude-code/ as they might be able to narrow down the issue further. I've checked all my tool names, and they are all under 64 characters and the server works fine in Claude Desktop, Cursor, Windsurf, so my feeling is this is an issue with Claude Code.

[SilverTab]

Got it! Thanks for looking into this! 🙏

[cameroncooke]

Fixed in 1.3.7 🎉

[SilverTab]

Fixed in 1.3.7 🎉

No way! Amazing.
Sucks that you had to make XcodeBuildMCP's tool names shorter when they should be within Anthropic's own API specs of 64char, but I definitely appreciate being unblocked. Thanks for all your great work on this project!

[cameroncooke]

Yeah I was worried the tool names wouldn’t be descriptive enough but it testing it seems fine. Will keep an eye on it though. Cameron.

…

On Thu, 8 May 2025 at 15:01, Jean-Nicolas Jolivet ***@***.***> wrote: *SilverTab* left a comment (getsentry/XcodeBuildMCP#3) <#3 (comment)> Fixed in 1.3.7 🎉 No way! Amazing. Sucks that you had to make XcodeBuildMCP's tool names shorter when they should be within Anthropic's own API specs of 64char, but I definitely appreciate being unblocked. Thanks for all your great work on this project! — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAEZ6SMFVKL6J3G4EY7IPNL25NPTRAVCNFSM6AAAAAB3ROB6EWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQNRTGE4DGMZQGE> . You are receiving this because you commented.Message ID: ***@***.***>

[jmanhype]

Okay, this is a crucial issue. If we could tag this issue in the other issues that I commented in about the 400 error with Claude code, it's related because I was able to get past this error once I removed all the MCP servers. So you were right.