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Grammarly does 5 jobs: grammar and spelling checks, style and clarity suggestions, AI rewriting and tone changes, works in the browser and other apps, plagiarism check. Most projects replace one or two of them, so pick the job you actually need.
Open-source alternatives to Grammarly that run locally, allow commercial use and need no paid API include Harper (grammar and spelling checks and works in the browser and other apps; Apache-2.0), Vale (style and clarity suggestions; MIT) and Lexicon (grammar and spelling checks and AI rewriting and tone changes; MIT code, Apache-2.0 weights). None of the 13 projects we track covers all 5 Grammarly jobs, so most people combine two or more.
Fast, offline English grammar and spell checker from Automattic, written in Rust, with browser extensions, editor plugins and a language server.
Widely used spell-checking library and command-line tool behind LibreOffice, Firefox and Chrome spell check, with dictionaries for many languages.
Rule-based grammar, spelling and style checker for 25+ languages; the core and HTTP server are open source (LGPL), Premium and AI rules are not.
Local-first desktop editor with LanguageTool proofreading plus offline AI rewrite, tone and summary tools from a bundled small LLM.
Language server and VS Code extension that runs LanguageTool offline to check grammar and spelling in LaTeX, Markdown, Typst and other markup.
Obsidian plugin that underlines grammar and spelling issues using the public LanguageTool API, LanguageTool Premium or your own server.
Self-hosted web front end for your own LanguageTool, Harper, LibreTranslate and Ollama servers to check grammar and translate text.
Python command-line linter for English prose that flags usage, cliché and style problems based on advice from well-known editors and usage guides.
Command-line spelling, grammar and style checker for LaTeX and Markdown files that maps LanguageTool results back to source lines.
Pluggable Node.js linter for natural-language text, like ESLint for prose; you install rules from npm for the checks you want.
Offline command-line prose linter that enforces a style guide (Microsoft, Google or your own rules) in your editor, in CI and on Markdown files.
Small Node.js linter for English prose that flags passive voice, weasel words, wordy phrases and similar style issues.
System-wide hotkey app that proofreads, rewrites and changes the tone of selected text using a local LLM (Ollama, MLX) or a cloud API.
No project meets all of your requirements. The list below shows what you'd need to relax.
We hid them because something is missing, unknown or conflicting. Here's what.
Yes. Writing Tools, LanguageTool, Harper, Lexicon and TeXtidote are free to download and run on your own computer without paid API keys. Each covers only part of what Grammarly does, so check which job you need.
Yes, with LanguageTool (LGPL-2.1-or-later), TeXtidote (GPL-3.0) and Writing Tools (GPL-3.0). Check the hardware notes and licence conditions on each page before you start.
Yes, with LanguageTool (LGPL-2.1-or-later), textlint (MIT) and Vale (MIT). Check the hardware notes and licence conditions on each page before you start.
Confirmed: Harper, Lexicon, proselint, textlint, Vale and write-good. With conditions: Hunspell, LanguageTool, LTeX+, LanguageTool Integration for Obsidian, OmniPoly, TeXtidote and Writing Tools. This is not legal advice; read each licence.
Not as of 2026-10-16. Grammar and spelling checks, style and clarity suggestions, AI rewriting and tone changes, works in the browser and other apps and plagiarism check are covered by different projects.