I Built a Fully Offline Grammarly Alternative as a Mac App — Without Writing a Single Line of Code
Imagine writing a complete article while seated on a turbulent airplane, with no internet connection, yet still having a reliable grammar checker at your fingertips. That is exactly what I did. Using only my voice and a conversational AI tool, I created a fully functional offline Grammarly alternative that runs directly on my Mac. No coding skills, no subscriptions, and no privacy compromises. Here is how it happened.
Why I Needed an Offline Grammar Checker
As a professional editor, I write constantly. Grammarly has been my go-to tool for years, but it comes with baggage. The constant need for an internet connection is a real pain point. On flights, in remote cafes, or anywhere with spotty Wi-Fi, I am left without help. Moreover, Grammarly’s recent shift toward AI-heavy suggestions has frustrated me. Sometimes it offers verbose rewrites that change my voice entirely. Other times, it misses basic spelling errors.
Privacy is another major concern. Every keystroke gets sent to the cloud for analysis. I wanted something that keeps my data local. Building my own offline grammar checker seemed like the perfect solution.
How I Built the App Without Any Coding
Claude AI Did All the Heavy Lifting
I started by opening the Claude mobile app on an Android tablet. I simply narrated my requirements: I wanted a spell-checking tool that works fully offline, is fast, and respects privacy. Claude suggested three possible approaches. I chose the one that used the Harper engine, an open-source grammar library acquired by Automattic in 2024.
Within 30 minutes, I had a working prototype. The first version ran as a standalone website in a browser tab, no internet required. The second became a Chrome extension. The final version is a full Mac menu bar app I named Quill. It combines note-taking with grammar correction and even offers one-click export to Apple Notes.
The entire process required zero lines of code from me. Claude generated the HTML, JavaScript, and configuration files. I only needed to open Xcode to build the app icon, which Claude also designed.
Why the Harper Engine Is a Game-Changer for Privacy
Automattic’s Harper engine processes everything locally on your device. It takes just 20 milliseconds to analyze text and suggest corrections. Unlike AI models that rely on token-based predictions, Harper uses hard-coded language rules. This means no verbose suggestions trying to change your writing style. It simply catches spelling mistakes and grammatical errors.
The trade-off? The app size increased from 10MB to 25MB when I embedded the Harper engine directly. But in an era where calculator apps can consume hundreds of megabytes, 25MB is negligible. The result is a privacy-first spell checker that never phones home with your data.
Limitations of My DIY Grammar Tool
Harper is not perfect. For example, it fails to flag obvious errors like “My name John” or “What your name?”. These basic subject-verb agreement issues slip through. However, for standard writing tasks, it catches the vast majority of typos and double spaces. The speed and offline capability more than compensate for these occasional misses.
Building on this, I have already tested the tool with half a dozen colleagues across Mac and Windows. They were impressed by its speed and accuracy. For anyone tired of subscription fees or privacy invasions, this approach offers a compelling alternative.
The Bigger Lesson: AI Puts You in Control
This experiment taught me something profound. The barrier to creating custom software has never been lower. A year ago, I would have laughed at the idea of building a Mac app from an Android tablet. Today, I have three working versions of my own offline Grammarly alternative.
Claude and similar AI tools are democratizing software development. You don’t need to learn Python or Swift anymore. You just need a clear idea and the willingness to describe it. This shift puts power back in the hands of everyday users.
If you are tired of cloud-dependent tools and want to explore offline productivity tools, consider building your own. Start with a simple project like a grammar checker. You might be surprised at what you can achieve.
For more on protecting your digital privacy, check out our guide on privacy-focused writing apps. And if you are curious about other AI-assisted projects, read about building apps without code.
