🐛 Bug: Tool Names Violate Gemini API Function Calling Rules

[darraghh1]

🐛 Bug: Tool Names Violate Gemini API Function Calling Rules

🔗 Issue Summary

The @21st-dev/magic@latest Model Context Protocol (MCP) server causes client applications using the Gemini API (such as the Gemini CLI) to fail initialization due to invalid function names starting with a digit. This is a compatibility issue with the Gemini API's strict validation rules for tool function declarations.

🔬 Environment & Configuration

• MCP Server: @21st-dev/magic@latest
• Client: Gemini CLI (using the standard Google Generative Language API)
• Client Behavior: Fails immediately upon startup when attempting to aggregate tools.

Relevant settings.json Snippet:

"magic": {
  "type": "stdio",
  "command": "cmd",
  "args": [
    "/c",
    "npx",
    "-y",
    "@21st-dev/magic@latest"
  ],
  "env": {
    "API_KEY": "..." // Key redacted, but present in configuration
  }
}

🛑 Error Description & Evidence

When the Gemini CLI starts, it receives a 400 Bad Request error. The Gemini API requires function names to follow the pattern: ^[a-zA-Z_][a-zA-Z0-9_]*$, meaning they cannot start with a digit (like '2').

API Error Message (from CLI debug output):

[API Error: [{
  "error": {
    "code": 400,
    "message": "The GenerateContentRequest proto is invalid:\n * tools[0].function_declarations[41].name: [FIELD_INVALID] Invalid function name. Must start with a letter or an underscore. Must be a-z, A-Z, 0-9, or contain underscores, dots and dashes, with a maximum length of 64.",
...
"status": "INVALID_ARGUMENT"
}]

Tools Exposed by magic Server (Verified via /mcp):

The following tools are exposed, and the ones starting with '2' are the source of the error:

1. 21st_magic_component_builder ❌ (Invalid: Starts with '2')
2. logo_search ✅ (Compliant)
3. 21st_magic_component_inspiration ❌ (Invalid: Starts with '2')
4. 21st_magic_component_refiner ❌ (Invalid: Starts with '2')

✅ Workaround

A temporary fix for users of the Gemini CLI is to explicitly exclude the non-compliant tools in their settings.json file:

"magic": {
  // ... existing config ...
  "exclude-tools": [
    "21st_magic_component_builder",
    "21st_magic_component_inspiration",
    "21st_magic_component_refiner"
  ]
}

💡 Proposed Solution

Please rename the affected tool functions within the @21st-dev/magic@latest package to be compliant with the Gemini API rules. A simple fix would be to prepend them with a non-digit character, for example: magic_21st_component_builder or _21st_magic_component_builder.