Claude Code MCP server auth errors show [object Object] in VS Code notifications

What this error means

MCP server error notification renders as "[object Object]" instead of error message is a Claude Code failure pattern reported for developers trying to fix claude code mcp server [object object] notification error. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Extension passes raw error object to vscode.window.showErrorMessage instead of err.message. Default JS coercion produces [object Object]. Errors are correctly logged in output channel. Affects MCP servers requiring OAuth (Google Calendar, Gmail).

Common causes

• When MCP servers require authentication but no OAuth token is configured, Claude Code shows a notification with literal [object Object] instead of the actual error. This fires every session start, is loud and repetitive, and gives users zero actionable information.
• Extension passes raw error object to vscode.window.showErrorMessage instead of err.message. Default JS coercion produces [object Object]. Errors are correctly logged in output channel. Affects MCP servers requiring OAuth (Google Calendar, Gmail).

Quick fixes

1. Confirm the exact error signature matches MCP server error notification renders as "[object Object]" instead of error message.
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. Verify the account session, API key, provider settings, and environment where the failing tool is running.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/anthropics/claude-code/issues/59102

Evidence note: Extension passes raw error object to vscode.window.showErrorMessage instead of err.message. Default JS coercion produces [object Object]. Errors are correctly logged in output channel. Affects MCP servers requiring OAuth (Google Calendar, Gmail).

Related errors

• Claude Code MCP server connection failure
• Claude Code VS Code notification format error

FAQ

What should I check first?

Start with the exact MCP server error notification renders as "[object Object]" instead of error message text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without MCP server error notification renders as "[object Object]" instead of error message.