Introduction

GrammarGem is a writing assistant for macOS that fixes your grammar, sharpens your tone, and rewrites anything — in every app — without your words ever leaving your Mac. It’s a one-time purchase, not a subscription, and it’s built in public.

Think of it as a private replacement for the cloud writing tools you already know. Everything that touches your text runs locally, so you get the speed of a native app and the calm of knowing nothing is uploaded, logged, or used to train a model.

How it works, in one sentence

Select text anywhere, press a global hotkey, and GrammarGem rewrites it in place — using a fast on-device grammar engine for instant corrections and a small local language model for rewrites, tone, and translation.

Two engines, one app

• Grammar (instant): a deterministic engine handles spelling, grammar, punctuation, phrasing, and repetition in milliseconds — fully offline, and free forever.
• AI (local): a small instruct model, downloaded once, powers clarity rewrites, tone shifts, “Ask” commands, translation, and Writing Modes — all on your Mac’s Neural Engine.

What GrammarGem doesn’t do

It doesn’t do cloud plagiarism scanning. That genuinely requires sending your writing to a server-side index, which would break the privacy promise — so it’s out of scope by design. Everything else you’d expect from a premium writing tool is here.