[BUG] FrontendRemoteMcpToolDefinition.name validation error on startup — tool name fails pattern ^[a-zA-Z0-9_-]{1,64}$

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?

Description

On every startup of Claude Desktop (Windows), a persistent warning toast appears:

tools.N.FrontendRemoteMcpToolDefinition.name: String should match pattern '^[a-zA-Z0-9_-]{1,64}$'

where N is a positional index that changes depending on how many MCP servers are loaded (observed: 48 with three MCP servers, 26 with one, 26 with zero user-configured MCP servers).

Key observation: the index shifts but the error persists regardless of which user-configured MCP servers are active — including when mcpServers is set to {} (empty). This rules out any user-side MCP server as the source and points to a built-in remote tool definition (FrontendRemoteMcpToolDefinition) served by Anthropic's backend.

Steps to reproduce

Install Claude Desktop on Windows 11.
Launch the app (any MCP server configuration, including none).
Warning toast appears immediately on startup.
Expected behavior

No validation error. All built-in remote tool definitions should have names conforming to ^[a-zA-Z0-9_-]{1,64}$.

Actual behavior

Warning toast on every launch. The app remains functional but the error is persistent and cannot be dismissed permanently.

Environment

OS: Windows 11 Home 10.0.26100
Claude Desktop version: latest (as of 2026-06-16)
MCP servers at time of report: kinsta only (also reproducible with empty mcpServers)

What Should Happen?

<img width="946" height="168" alt="Image" src="https://github.com/user-attachments/assets/dfb613c1-1056-41c9-9791-5d1c0129f8f8" />

Error Messages/Logs

Description

On every startup of Claude Desktop (Windows), a persistent warning toast appears:

tools.N.FrontendRemoteMcpToolDefinition.name: String should match pattern '^[a-zA-Z0-9_-]{1,64}$'

where N is a positional index that changes depending on how many MCP servers are loaded (observed: 48 with three MCP servers, 26 with one, 26 with zero user-configured MCP servers).

Key observation: the index shifts but the error persists regardless of which user-configured MCP servers are active — including when mcpServers is set to {} (empty). This rules out any user-side MCP server as the source and points to a built-in remote tool definition (FrontendRemoteMcpToolDefinition) served by Anthropic's backend.

Steps to reproduce

Install Claude Desktop on Windows 11.
Launch the app (any MCP server configuration, including none).
Warning toast appears immediately on startup.
Expected behavior

No validation error. All built-in remote tool definitions should have names conforming to ^[a-zA-Z0-9_-]{1,64}$.

Actual behavior

Warning toast on every launch. The app remains functional but the error is persistent and cannot be dismissed permanently.

Environment

OS: Windows 11 Home 10.0.26100
Claude Desktop version: latest (as of 2026-06-16)
MCP servers at time of report: kinsta only (also reproducible with empty mcpServers)

Steps to Reproduce

Description

On every startup of Claude Desktop (Windows), a persistent warning toast appears:

tools.N.FrontendRemoteMcpToolDefinition.name: String should match pattern '^[a-zA-Z0-9_-]{1,64}$'

where N is a positional index that changes depending on how many MCP servers are loaded (observed: 48 with three MCP servers, 26 with one, 26 with zero user-configured MCP servers).

Key observation: the index shifts but the error persists regardless of which user-configured MCP servers are active — including when mcpServers is set to {} (empty). This rules out any user-side MCP server as the source and points to a built-in remote tool definition (FrontendRemoteMcpToolDefinition) served by Anthropic's backend.

Steps to reproduce

Install Claude Desktop on Windows 11.
Launch the app (any MCP server configuration, including none).
Warning toast appears immediately on startup.
Expected behavior

No validation error. All built-in remote tool definitions should have names conforming to ^[a-zA-Z0-9_-]{1,64}$.

Actual behavior

Warning toast on every launch. The app remains functional but the error is persistent and cannot be dismissed permanently.

Environment

OS: Windows 11 Home 10.0.26100
Claude Desktop version: latest (as of 2026-06-16)
MCP servers at time of report: kinsta only (also reproducible with empty mcpServers)

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.12603.1 Claude Chat

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_