Description

I get an MCP Validation Error on lint failure when using the MCP server function.
As far as I have confirmed, it occurs with the following Tool.

• LintText
• getLintFixedFileContent
• getLintFixedTextContent

Steps to Reproduce

In the case of lintText Tools, the following steps are explained.

1. start MCP server via AI agent 2.
2. generate a lint error. For example, lint Markdown with no .md plugin. 3.
3. textlint MCP server returns Validation Error: data should NOT have additional properties.

Expected Behavior

Validation Error is not generated.

Actual Behavior

Validation Error.
The error message is
Structured content does not match tool's output schema: data.results[0].messages[0] should not have any additional properties.

Screenshots

Environment

• OS: Ubuntu 24.04.02 LTS

What version of textlint are you using?

• textlint 15.1.0

What file type (Markdown, plain text, etc.) are you using?

• Markdown, plain text