The reason to leave Grammarly is rarely the quality of its suggestions. It is that every draft has to travel through a cloud service that analyzes the text, which is hard to square with legal, medical, source-code, or unreleased product writing, and its confident rewrites nudge everyone toward a house style no one actually defined. Open source grammar and style tools change that in two ways. They can run entirely on your own machine or infrastructure, so sensitive text never leaves, and their rules, dictionaries, and editor integrations are things you tune rather than a vendor's model you accept. The trade is usually less hand-holding polish in exchange for control over what gets flagged and where checking happens.
LanguageTool is open-source proofreading software for English, Spanish, French, German, Portuguese, Polish, Dutch, and more than 20 other languages. It finds many errors that a simple spell checker cannot detect, covering grammar, punctuation, spelling, and style issues for multilingual writing.
Harper is an open-source English grammar and spell checker for developers and writers. It is designed to lint writing locally instead of sending text to a server, addressing privacy and latency concerns in server-based grammar tools.
Vale is a command-line tool that brings code-like linting to prose. It helps teams check documentation and other written content with repeatable rules instead of editor-specific suggestions. It runs on Windows, macOS, and Linux and is written in Go.
These three tackle different halves of Grammarly: language coverage, privacy, and enforceable style.
Broad, multilingual coverage: LanguageTool LanguageTool checks grammar, punctuation, spelling, and style in more than 30 languages and finds errors a plain spell checker misses. You can use its HTTP API, embed it via Java, or run your own LanguageTool server, which keeps checking on infrastructure you control while covering many languages at once.
Private, on-device checking: Harper Harper lints English writing locally in a Rust core that loads through WebAssembly, so text never leaves your machine. It covers US, UK, Canadian, Australian, and Indian English and ships a language server for editors like VS Code, Neovim, and Obsidian, which suits confidential drafts and developer workflows.
House style as code: Vale Vale brings code-style linting to prose, applying standard editorial style guides or your own in-house rules without changing the tool itself. It is markup-aware, so it excludes code snippets, and ships as a stand-alone binary with no Python or Node runtime, making it a natural fit for documentation review in CI.
Grammarly is less a single grammar checker than a typing layer spread across browsers, editors, email, and mobile keyboards, so the first decision is which of those surfaces you actually need to cover. Open source tools tend to specialize. LanguageTool checks grammar, punctuation, style, and spelling in more than 30 languages and can run as your own server or through an API, which fits broad, multilingual coverage. Harper runs entirely on your device in a small Rust and WebAssembly core, which suits confidential English writing and editor integrations. Vale treats prose like code, applying style rules you define, which fits documentation teams and CI pipelines.
The biggest thing you give up is not basic grammar but managed polish. Grammarly bundles cloud processing, tone hints, explanations, and rewrite suggestions into one smooth experience. Open source options often ask you to choose between privacy, configurability, and convenience: some flag fewer style issues, some over-report rules your team does not care about, and most need tuning before they stop fighting your house style. Rewrite quality in particular is where a local tool is usually weaker than a cloud model.
Migration is light, because Grammarly is not the system of record for your writing. Copy out any drafts you keep in its editor, then rebuild the parts that live in your account, since personal dictionary entries, ignored suggestions, and tone preferences generally have to be recreated by hand. The upside is that a tool like Vale keeps rules and dictionaries in version control, so your house style becomes reviewable files instead of settings locked in a dashboard. Remove the extensions and keyboards only after the replacement works where you write most.
Yes, with the right tool. Harper analyzes text on your device in a Rust and WebAssembly core and does not send writing to a server, which suits confidential drafts and locked-down environments. LanguageTool can also be self-hosted so text stays on infrastructure you control. Verify offline behavior by disconnecting the network, not just by reading a settings page.
It depends on what you mean by accurate. Basic spelling, grammar, and punctuation can be solid, but context-aware rewrites and tone judgment are harder. Test with your own writing, including technical terms and long documents, and count false positives as carefully as missed errors, because a noisy checker gets switched off. LanguageTool tends to be the strongest general grammar option here.
Coverage varies and is rarely identical across every text box. Check whether suggestions appear inline, in a sidebar, or only after you paste into an editor. Harper ships editor integrations through harper-ls for tools like VS Code, Neovim, and Obsidian rather than blanket browser coverage, so map the exact places you write before assuming parity with Grammarly's reach.
Yes, and this is where open source pulls ahead. Vale applies standard editorial style guides or your own in-house rules, is markup-aware so it skips code snippets, and runs from the command line. That lets you gate documentation in CI and keep terminology consistent, turning a vague house style into explicit rules the whole team can review.
LanguageTool is the multilingual option, covering grammar and style in more than 30 languages and finding errors a plain spell checker misses. Harper focuses on English but across US, UK, Canadian, Australian, and Indian variants. Vale checks against style rules rather than grammar, so its language coverage depends on the rule sets you configure rather than a built-in model.
Yes, and it is a common reason to leave Grammarly. Vale ships as a stand-alone binary with no Python or Node runtime and lints prose in a pipeline, while Harper provides a language server for editor integrations. Decide your failure policy - block a build, post warnings, or only run on documentation changes - and keep custom dictionaries in version control.
Mostly no. LanguageTool, Harper, and Vale focus on grammar, spelling, punctuation, and style-rule enforcement rather than generative rewriting or tone scoring. If assertive rewrite suggestions and tone feedback are central to how you write, that is the capability you will miss most, and no tool here reproduces it fully. Plan to do that judgment yourself.
