OpenGrammar

What does OpenGrammar do?

OpenGrammar describes itself as a "privacy-first, offline-capable Turkish and English intelligent spelling, grammar and AI writing assistant." It installs as a Chrome extension on Manifest V3 and adds a floating badge inside Gmail, Twitter and X, LinkedIn, WhatsApp Web and web forms. The badge underlines errors and suggests fixes.

Two feature groups make the project worth reading. The first is Turkish-specific rules: over 100 common word fixes, question-particle disambiguation ("mi", "mı", "mu", "mü" separated correctly), conjunction and punctuation checks, and a personal dictionary for the user's own terms. The second is an optional tone transformer that calls Gemini through the user's own key, for formal, polite or shorter rewrites and for summaries. The tone transformer is online; the grammar checker is on the device.

Key facts

• Licence: MIT.
• Platform: Chrome and Chromium-based browsers, Manifest V3.
• Default language model: on-device dictionaries for Turkish and English.
• Fixes: over 100 common Turkish word fixes.
• Grammar rules: question-particle disambiguation (mi, mı, mu, mü), conjunctions, punctuation.
• Supported surfaces: Gmail, Twitter and X, LinkedIn, WhatsApp Web, generic web forms.
• Personal dictionary: user can add own terms.
• AI tone transformer: optional, Gemini API, user key.
• Install: Chrome Web Store page in the README, or load unpacked.
• Processing: on the device by default. No data is transmitted on the grammar path.

What does it replace, and where does it fall short?

OpenGrammar replaces Grammarly for Turkish and English writers who want grammar and spelling inside a browser, with no account and no telemetry.

Where it falls short: Chrome and Chromium-based browsers only. Firefox and Safari are not supported, and there is no desktop app, so Microsoft Word, Google Docs offline, and native email clients are out of scope. The grammar rules are tuned for Turkish; English is covered but the project's own value lies in the Turkish rules, which no commercial Grammarly path covers at the same depth. The AI tone transformer calls Gemini with the user's key, which is online and not free beyond Google's free tier.

How does OpenGrammar run?

Install the extension from the Chrome Web Store, or load the unpacked repository in Chrome's developer mode. Grant the extension permission for the sites on which it should run.

A floating badge appears on supported sites. Typed text is checked against the on-device grammar and spelling rules, and suggestions are shown inline. The tone transformer is a separate menu item that calls Gemini with the user's API key; a user who does not want that feature can leave the key field empty and use only the grammar checker.

Who is OpenGrammar for?

A Turkish writer who uses Gmail, LinkedIn or WhatsApp Web in Chrome and wants grammar and spelling checked on the device. An English-only user has more polished options, such as Harper, Vale or LanguageTool. A reader who does not use Chrome, or who writes in Microsoft Word, should look at those projects too.

What limits does the README state?

• Chrome and Chromium browsers only.
• No desktop app and no mobile version.
• Grammar rules are focused on Turkish and English; other languages are not covered.
• The AI tone transformer uses Gemini through the user's key and is online.
• Processing stays on the device on the grammar path; no telemetry is sent on the grammar checks.

Questions people ask

Is OpenGrammar open source?

Yes. The LICENSE file at the repository root is MIT, an OSI-approved licence. The code is JavaScript with Chrome extension manifests. The on-device grammar rules are part of the extension package; the AI tone transformer is an optional path that calls Gemini with a key the user provides.

Does OpenGrammar work offline?

Yes for the grammar and spelling path. The README says processing is 100 percent offline and local for grammar checks, and no data is transmitted on that path. The optional AI tone transformer calls Gemini and is online; a user who turns it off has a fully offline tool.

Can OpenGrammar be used commercially?

Yes. MIT allows commercial use. A Turkish-language business can install the extension across a team without a fee. The optional Gemini feature uses the user's own Gemini key, which has Google's own commercial terms through its API pricing.

How does OpenGrammar compare with Grammarly?

Grammarly is a hosted writing assistant for English, Spanish, German and French, with a browser extension and desktop app, and a monthly subscription. OpenGrammar is an open Chrome extension with strong Turkish rules, on-device grammar checks, and an optional Gemini path for rewrites. The trade is: Grammarly's polish and language coverage against OpenGrammar's Turkish depth, privacy and zero cost. The open-source alternatives to Grammarly page sets it beside Harper, Vale and LanguageTool.

What is the "mi/mı/mu/mü" separation rule?

Turkish has a question particle that changes vowel (i, ı, u or ü) depending on vowel harmony, and that is written separately from the verb it follows. Many users write it joined, which is a common Turkish spelling mistake. OpenGrammar detects when the particle is joined and suggests the correct separated form; the README names this rule as one of the Turkish-specific features.

Sources

• OpenGrammar README and LICENSE: github.com/codumtr/opengrammar, read 2026-11-09.