Cursor / Cursor
Cursor Error Connecting to StreamableHttp MCP Server — Icon Sizes Field Validation Failure
Fix Cursor MCP streamableHttp connection error with icon sizes field Includes evidence for Cursor troubleshooting demand.
- Category
- Cursor
- Error signature
Cursor error connecting to streamableHttp MCP server — sizes field validation- Quick fix
- Compare the failing environment with a known working setup, then change one configuration value at a time.
- Updated
What this error means
Cursor error connecting to streamableHttp MCP server — sizes field validation is a Cursor failure pattern reported for developers trying to fix cursor mcp streamablehttp connection error with icon sizes field. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.
Why this happens
Cursor MCP client rejects server responses containing ‘sizes’ field in icon configuration. Home Assistant MCP integration affected. Workaround pending since January 2026.
Common causes
- Cursor fails to connect to streamableHttp MCP servers due to icon configuration containing unexpected ‘sizes’ field, causing validation errors in the MCP client
- Cursor MCP client rejects server responses containing ‘sizes’ field in icon configuration. Home Assistant MCP integration affected. Workaround pending since January 2026.
Quick fixes
- Confirm the exact error signature matches
Cursor error connecting to streamableHttp MCP server — sizes field validation. - Check the Cursor account, local tool state, and provider configuration involved in the failing workflow.
- Compare the failing environment with a known working setup, then change one configuration value at a time.
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
- Capture the exact error message and the command, editor action, or request that triggered it.
- Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
- Review the source evidence below and compare it with your environment.
- Apply one change at a time and rerun the smallest failing action.
- 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
Evidence note: Cursor MCP client rejects server responses containing ‘sizes’ field in icon configuration. Home Assistant MCP integration affected. Workaround pending since January 2026.
Related errors
- Cursor MCP server error No server info found
- MCP protocol validation errors
FAQ
What should I check first?
Start with the exact Cursor error connecting to streamableHttp MCP server — sizes field validation text and the smallest action that reproduces it.
Can I ignore this error?
No. Treat it as a failed Cursor 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 Cursor error connecting to streamableHttp MCP server — sizes field validation.