[MCP tool boolean parameter always serialized as string, causing "Expected bool, got string" error]

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When calling an MCP tool that requires a boolean parameter, the value is always sent to the MCP server as a string ("true", "True", "1"), never as a native JSON boolean — the tool rejects the call with a type validation error.

Affected tool: ads_boost_ig_post, from the Meta Ads MCP (server id 97087554-d6e2-4022-b05d-0d227ea3758a), parameter confirmed.

What Should Happen?

The confirmed parameter should be serialized as a native JSON boolean when the tool call is sent, so the MCP server accepts it and the tool call succeeds.

Error Messages/Logs

Invalid value for `confirmed`. Got: 'true'. Error: Expected bool, got string

Steps to Reproduce

1. Connect to an MCP server that exposes a tool with a required boolean parameter (in this case, ads_boost_ig_post from the Meta Ads MCP, parameter confirmed)
2. Call the tool with confirmed=true
3. Observe the error: "Invalid value for confirmed. Got: 'true'. Error: Expected bool, got string"
4. Retry with confirmed=True and confirmed=1 — same error in both cases
5. Note: the tool's schema, when inspected via ToolSearch, appears generic ({"type": "object"}, no per-field types) — this may be why the client doesn't know to serialize this field as a boolean

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.232 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Full investigation writeup available if needed — happy to share more context/repro details.