Obsidian is my favorite productivity tool. I use it for all of my writing, as a journaling app, and to replace multiple productivity tools. There's a big downside, though: no grammar checking tool.Grammarly is the best known grammar checking tool, but there's no way to add it to Obsidian. I also wouldn't enable it even if I could. Grammarly processes text on their own servers, which is a potential privacy issue and also generally inefficient. This is why I've come to love Harper, a free and open-source alternative that runs entirely on your device and can be added to Obsidian in a couple of clicks.Harper isn't just an Obsidian tool—there are also plugins for WordPress, Visual Studio Code, or any developer tool that supports the Language Server Protocol. If you'd like to see Harper in action before installing, there's a live demo on the Harper homepage—just type whatever you want and watch the recommendations.The Harper plugin for Obsidian can easily be installed from the Community Plugins tab in the Obsidian settings, the way you'd install any other extension. After you download and activate the plugin it will start working immediately.Harper can make spelling recommendations, while also pointing out grammatical and stylistic issues. I've been trying out Harper for a week now after missing a couple of embarrassing typos. It's helped me notice easy-to-overlook issues while, for the most part, staying out of my way.Potential issues are underlined. Hover the mouse over any highlighted issue and you'll see an explanation and suggestions. Credit: Justin Pot I find Harper noticeably faster than web-based tools, which makes sense, given that the developer was primarily motivated by speed during development. In the settings you can choose between American, Canadian, Australian, and British English. You can also change the settings for a specific Harper rule, allowing you to do things like use the Oxford comma. Right now Harper isn't easy to use outside of Obsidian—there's no browser extension. But if you do your writing in Obsidian, or are a developer who uses a supported IDE, Harper is a tool that integrates into your workflow right now—one well worth trying out.