What they did
The poster, u/jaklimoff, talks to Claude in English all day but noticed their mistakes never got pointed out, because Claude understood them anyway. They used Claude Code to build a plugin for Claude Code itself. After each prompt is sent, a hook passes the text to a small Haiku call inside the same session. A few seconds later a dim line appears below the prompt with errors struck through, the fixes, a short reason and, now and then, a more natural rewrite. The prompt itself is never held back. Claude Code wrote most of the code and the tests, and recorded the demo GIF with the vhs terminal recorder. The plugin is one file, MIT licensed, installed from its own plugin marketplace, and can be switched off with a slash command.
How it went
The plugin shipped and is public on GitHub. The poster says tuning the proofreading prompt took more effort than the code: the hard part was stopping it from flagging lowercase, casual punctuation, dropped apostrophes, slang, code and pasted logs. Commenters, including native speakers, said they would install it. There are no numbers on accuracy or cost yet.
Worth knowing
Every prompt costs one extra Haiku call through your existing Claude Code session. The list of things it ignores has no setting; the poster says to edit the prompt at the top of the hook file to change it.