MCP tool parameters sent as strings instead of integer/boolean types causing Zod validation failures

What this error means

Zod literal validation failures: MCP tool parameters with integer/boolean types are sent as strings is a Cline (Claude Code) failure pattern reported for developers trying to fix type serialization bug where cline sends numeric and boolean parameters as strings to mcp servers, causing client-side validation failures. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #10203 in cline/cline (opened Apr 9, 2026). Type coercion bug in MCP protocol serialization causes downstream validation failures. 1 comment, VS Code specific label. Impacts developers using custom MCP servers with typed schemas. Distinct from the task_progress issue (#10737). Maps to ‘AI Coding Tools’.

Common causes

• GitHub issue #10203 in cline/cline (opened Apr 9, 2026). Type coercion bug in MCP protocol serialization causes downstream validation failures. 1 comment, VS Code specific label. Impacts developers using custom MCP servers with typed schemas. Distinct from the task_progress issue (#10737). Maps to ‘AI Coding Tools’.

Quick fixes

1. Confirm the exact error signature matches Zod literal validation failures: MCP tool parameters with integer/boolean types are sent as strings.
2. Check the Cline (Claude Code) account, local tool state, and provider configuration involved in the failing workflow.
3. 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

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/cline/cline/issues/10203

Evidence note: GitHub issue #10203 in cline/cline (opened Apr 9, 2026). Type coercion bug in MCP protocol serialization causes downstream validation failures. 1 comment, VS Code specific label. Impacts developers using custom MCP servers with typed schemas. Distinct from the task_progress issue (#10737). Maps to ‘AI Coding Tools’.

Related errors

• AI Coding Tools

FAQ

What should I check first?

Start with the exact Zod literal validation failures: MCP tool parameters with integer/boolean types are sent as strings text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Cline (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 Zod literal validation failures: MCP tool parameters with integer/boolean types are sent as strings.