gemini-cli - 💡(How to fix) Fix Bug: ACP handshake requires numeric protocolVersion instead of string

Because modern MCP clients send a date string, the Gemini CLI server rejects the request with a Zod type mismatch error, making it incompatible with standard MCP SDKs without manual transport-level interception.

TL;DR

Update the Gemini CLI to accept the protocolVersion as a string instead of a number to ensure compatibility with the MCP 1.0 standard.

Guidance

• The issue arises from a type mismatch between the expected number and the sent string for the protocolVersion in the initialize handshake.
• To verify the issue, send a standard MCP initialize request with a string protocolVersion and observe the failure.
• A potential workaround is to modify the client-side code to send the protocolVersion as a number, but this would require changes to the MCP client libraries.
• Another approach is to update the Gemini CLI to use a more permissive schema for the protocolVersion, allowing both numbers and strings.

Example

// Example of a modified initialize request with a numeric protocolVersion
{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "initialize",
    "params": {
        "protocolVersion": 1,
        "capabilities": {},
        "clientInfo": { "name": "test-client", "version": "1.0.0" }
    }
}

Notes

The provided solution assumes that the Gemini CLI can be updated to accept a string protocolVersion. If this is not possible, alternative workarounds such as transport-level interception may be necessary.

Recommendation

Apply a workaround by modifying the client-side code to send the protocolVersion as a number, as this is a more feasible short-term solution. However, it is recommended to update the Gemini CLI to accept the protocolVersion as a string in the long term to ensure compatibility with the MCP 1.0 standard.