Can't invoke MCP Server tool

[TylerLeonhardt]

Describe the bug

Can't invoke an MCP server tool

Affected version

0.0.342 Commit: 69ac520

Steps to reproduce the behavior

● Configured MCP servers: vscode-playwright-mcp

 ● Connected to GitHub MCP Server

 ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
 │ > start the vscode automation                                                                                                       │
 ╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

 ● I'll start the VS Code automation for you.

 ✗ Execution failed: Cannot read properties of undefined (reading 'type')

 ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
 │ > what tools do you have                                                                                                            │
 ╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

 ● I have access to the following tools:

   File Operations:

     - str_replace_editor - View, create, and edit files with precise string replacements

   Command Execution:

     - bash - Run commands in an interactive Bash session (supports both sync and async modes)
     - write_bash - Send input to running async commands
     - read_bash - Read output from async commands
     - stop_bash - Stop running async commands

   GitHub Operations:

     - Repository exploration (get file contents, commits, branches, tags)
     - Issue management (list, get, search issues and comments)
     - Pull request operations (list, search, get details, diffs, reviews)
     - Workflow and CI/CD (list workflows, runs, jobs, artifacts, logs)
     - Code scanning and security alerts
     - Release management
     - Code and repository search

   VS Code Automation:

     - vscode-playwright-mcp-vscode_automation_start - Start VS Code with Playwright automation (with optional video recording)

   Web Search:

     - web_search - AI-powered web search for current information with citations

   I'm particularly well-equipped for working with the VS Code codebase, as I can
   run builds, tests, linters, search code, make surgical edits, and validate
   changes through the watch task system.

 ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
 │ > run this one vscode-playwright-mcp-vscode_automation_start                                                                        │
 ╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

 ✗ Execution failed: Unexpected end of JSON input

Expected behavior

tool calls work

Additional context

Logs:

2025-10-16T16:21:21.867Z [INFO] Starting Copilot CLI: 0.0.342
Commit: 69ac520
2025-10-16T16:21:21.867Z [INFO] Node.js version: v22.20.0
2025-10-16T16:21:22.134Z [LOG] Starting MCP client for vscode-playwright-mcp with command: sh and args: /Users/tyleonha/Code/Microsoft/vscode/test/mcp/scripts/start-stdio.sh
2025-10-16T16:21:22.134Z [LOG] Starting MCP client for vscode-playwright-mcp with command: sh and args: /Users/tyleonha/Code/Microsoft/vscode/test/mcp/scripts/start-stdio.sh
2025-10-16T16:21:22.135Z [LOG] Creating MCP client for vscode-playwright-mcp...
2025-10-16T16:21:22.136Z [LOG] Connecting MCP client for vscode-playwright-mcp...
2025-10-16T16:21:26.275Z [INFO] Using default model: claude-sonnet-4.5
2025-10-16T16:21:26.397Z [LOG] MCP client for vscode-playwright-mcp connected, took 4261ms
2025-10-16T16:21:26.397Z [LOG] Started MCP client for vscode-playwright-mcp
2025-10-16T16:21:26.569Z [INFO]  
2025-10-16T16:21:26.657Z [LOG] Using Copilot API endpoint: https://api.enterprise.githubcopilot.com/mcp/readonly
2025-10-16T16:21:26.657Z [LOG] Starting remote MCP client for github-mcp-server with url: https://api.enterprise.githubcopilot.com/mcp/readonly
2025-10-16T16:21:26.658Z [LOG] Creating MCP client for github-mcp-server...
2025-10-16T16:21:26.658Z [LOG] Connecting MCP client for github-mcp-server...
2025-10-16T16:21:27.132Z [LOG] MCP client for github-mcp-server connected, took 474ms
2025-10-16T16:21:27.132Z [LOG] Started MCP client for remote server github-mcp-server
2025-10-16T16:21:27.132Z [LOG] GitHub MCP server configured after authentication
2025-10-16T16:21:29.925Z [INFO] [log_2d7097, x-request-id: "00000-17156943-bda2-46fe-9d16-bd2b2bcd8491"] post https://api.enterprise.githubcopilot.com/chat/completions succeeded with status 200 in 2910ms

2025-10-16T16:21:31.955Z [ERROR] error
2025-10-16T16:21:31.956Z [ERROR] {
  "cause": {}
}
2025-10-16T16:21:35.564Z [INFO] Using default model: claude-sonnet-4.5
2025-10-16T16:21:35.564Z [INFO]  
2025-10-16T16:21:39.143Z [INFO] [log_d4a4e3, x-request-id: "00000-423c2c30-5664-49d9-b1fe-4d1384013ed8"] post https://api.enterprise.githubcopilot.com/chat/completions succeeded with status 200 in 3403ms

2025-10-16T16:21:40.181Z [ERROR] error
2025-10-16T16:21:40.181Z [ERROR] {
  "cause": {}
}

macOS ARM
VS Code Terminal
zsh

[EvanBoyle]

We're currently on an MCP quality push and hope to address this soon

[RobertSundling]

It seems that this has really become a problem with 0.0.348.

I am consistently getting

Execution failed: Unexpected end of JSON input

after only five or six things happen, such as listing directories. I don't know if it's MCP related (I am using a local MCP server, but it doesn't seem to be failing on my local MCP calls, although it does make some earlier) or if it's more general. I'd never seen this before 0.0.348. It has made this essentially unusable, so I just switched back to 0.0.347 which continues to work fine.

[RobertSundling]

Update 0.0.350 solved the Execution failed: Unexpected end of JSON input problem for me. (Haven't tried 0.0.351 yet.)

[TylerLeonhardt]

Yes this is fixed now