grammai is a free open-source Grammarly alternative that works offline

A browser-based grammar checker reads every sentence the user types. grammai, a new Chrome extension, does the same job on the user's own machine. The spelling and grammar engines come inside the extension, the dictionaries for English and German are bundled, and the README states that ordinary checks "stay inside your browser" with "no account or extra software". The repository had 106 stars and 14 forks within a day of its first push, under GPL-3.0.

The author, who publishes under the GitHub name zilvestro, calls it "AI writing assistance. Free & open source." in the project's own words. The README names the comparison it is aimed at: "grammai is an independent project and is not affiliated with Grammarly, LanguageTool, Anthropic or OpenAI."

What runs on the device, and what reaches a provider

Spelling and grammar are local. The German engine takes a few seconds to initialise on its first check, and the README names contextual rules such as the correction of "Ist das wirklich war?" to "Ist das wirklich wahr?" as an example of what the local engine catches. Local grammar coverage is limited, the project states, and does not claim parity with Grammarly or LanguageTool.

The AI features are opt-in and route through a Claude Code or Codex command-line tool the user has already signed into. The README is specific on what that means: "Optional AI features use your own signed-in Claude Code or Codex CLI. Your provider's access requirements and usage limits apply; grammai does not include an AI subscription." A one-time local helper installer, currently macOS only, bridges the extension to the installed CLI. The three AI actions are rewrites, English-to-German or German-to-English translation, and a context check across a passage that the local rules alone cannot judge.

Scope today, and what is not covered

The author lists the beta scope in the README. Standard textareas, suitable text inputs, contenteditable fields and tested Draft.js editors, including X-style ones, work. "Dedicated Google Docs canvas support and general Shadow DOM, Slate and ProseMirror adapters are not complete." Language detection can be ambiguous on short or mixed-language text. The project is a Chrome Web Store "coming soon" listing and installs today by building from source with Node.js 22 or newer and loading the unpacked dist directory from chrome://extensions.

A short privacy section says grammai has no analytics, no telemetry and no automatic crash uploads. Preferences, personal words, saved prompts and paused hostnames stay in local extension storage. An explicit AI action sends only the selected text, or the active field if no text is selected, to the provider the user chose.

For a team already paying for Claude Code or Codex

A paid grammar seat costs money every month, and the data goes to a service whose only job is to read it. For a developer who already pays for Claude Code or Codex, grammai pushes the AI calls through that account instead, so a rewrite or a translation is charged against the plan the user already has. The free local engine covers the common corrections a writer needs on a comment, a chat message, a commit note or an email, with no account at all. The test takes one install.

Source

zilvestro/grammai on GitHub.