According to the spec, yes a grammar checker would be subject to disclosure:
> ai-modified Indicates AI was used to assist with or modify content primarily created by humans. The source material was not AI-generated. Examples include AI-based grammar checking, style suggestions, or generating highlights or summaries of human-written text.
> ai-modified Indicates AI was used to assist with or modify content primarily created by humans. The source material was not AI-generated. Examples include AI-based grammar checking, style suggestions, or generating highlights or summaries of human-written text.