Margin: AI second pass for Harper

Margin catches what Harper's rules can't: agreement across clauses, tense, wrong-but-real words ("effect" for "affect" in context), missing or repeated words, run-ons and comma splices. Harper stays in charge of spelling and mechanical grammar; Margin never repeats what Harper already flags. This extension installs Harper too.

Margin is independent and not affiliated with Harper or Automattic.

Setup

Run Margin: Choose where text is checked… (or click "Margin" in the status bar):

• Gemini API (Gemma 4), tested. Paste a Gemini API key (stored in VS Code's secret storage). The sentences being checked are sent to Google; on the free tier Google may use them to improve its products. Code, URLs and emails are masked first.
• Local server (Ollama / LM Studio), untested. Text stays on your machine. It's implemented, but the maintainer hasn't been able to test it. Please report how it goes.

Nothing is sent until you choose. Files matching margin.excludeGlobs are never sent, and Margin is off in untrusted workspaces.

Use

Suggestions appear as underlines a couple of seconds after you stop typing (margin.trigger: idle, save or manual). The quick fix (Ctrl+.) offers: apply the change, fix the whole sentence, or ignore.

Rewrite selection (right-click, or the command palette): Improve, Concise, Formal, Friendly, Fix only, or your own instruction. The result streams into a side-by-side diff; accept or reject it. Margin warns you if a rewrite changed numbers, negation or code/links.

Cache. To avoid re-sending text, Margin remembers which sentences needed no change: only a hash and a date, stored in VS Code's extension storage, kept for 30 days. Fixes are kept in memory only. Margin: Clear cache removes it.

Honest status

Early. Tested with hosted Gemma 4 26B A4B on synthetic text. The local path is untested. Margin has no telemetry and never logs your text.