Tools function definitions: responseJsonSchema returned instead of response when using mcpToTool breaking my client

[gsans]

Environment details

• Programming language: TypeScript
• Package version: 1.9.0

Steps to reproduce

This error happens when trying to migrate a client from an older version to a newer one. This is related to MCP configuration changes between versions.

1. Upgrade genai client from 1.8.0 to 1.9.0 or 1.10.0. No other changes.
2. Try MCP tools defined. Query: What’s the temperature in London?
3. The main difference I’ve seen is the configuration request which has changed from using response to responseJsonSchema.
4. There may be other issues but the function definition and the client stopping to respond to tool usage is enough.

Reproducible environment

Repo: https://github.com/gsans/gemini-2-live-angular

Exact line:
https://github.com/gsans/gemini-2-live-angular/blob/bfde02f15a5df8c73446ac63e488f55584fc0739/src/gemini/gemini-mcp.service.ts#L27

Developer Tools: check the WebSocket requests.

[gsans]

Diff check for the configuration request for easy reference. You can see the differences between version 1.8.0 and 1.9.0.

https://gist.github.com/gsans/64d1a1f89eb22bd7ece4999004d852ee/revisions

Being the version number the only change in the project I would like to know how to change my configuration so it can work with JSON schema or alternatively set the default to use the legacy parameters and only create the parametersJsonSchema when we opt in via flag or similar when calling to mcpToTool.

Let me know how I should proceed to update my project.