Isn't this pretty much why language models were invented?

Pasting something directly into the chat interface seems weird, but if you could somehow just see where P(token | context) falls off a cliff, that's a pretty good hint that your writing has problem.

Yeah, but for this use case you don't need Claude. You probably want a tuned lightweight small model that can run locally.

Even Haiku is massive overkill for this use case.