This Free Tool Kills Grammarly's Edge

Grammarly operates as a keylogger you pay for, a blunt claim directly supported by its own documentation. Everything you type—from casual notes to sensitive documents—ships to their servers and is stored there, fundamentally compromising your data privacy. This cloud-based model means every keystroke and draft leaves your local machine, residing instead on a third-party server, despite users paying over $140 annually for this exposure.

Beyond the inherent data exposure, Grammarly’s reliance on machine learning models often delivers frustratingly inconsistent advice. Users frequently report the tool suggesting they delete a comma at one moment, then instructing them to put it back the next, a clear example of its "changing its mind" behavior. This unpredictable feedback erodes trust and hinders a predictable writing workflow.

Ultimately, users are paying a premium subscription—over $140 a year—for a writing assistant that compromises both privacy and predictability. This expensive service not only processes and stores sensitive user text remotely but also delivers inconsistent, machine learning-driven guidance. The core problem is clear: a tool designed to enhance writing instead introduces significant data security concerns and unreliable assistance.

Meet Harper, a free, open-source grammar checker built with privacy in mind. Crafted in Rust, Harper functions entirely offline, ensuring your sensitive text never leaves your local machine. This fundamental design choice directly addresses the data privacy concerns inherent in cloud-dependent services like Grammarly.

At its core lies a powerful rule-based engine, a deliberate departure from AI-driven models. This deterministic system processes your writing through approximately 287 handwritten Rust rules, guaranteeing consistent suggestions without the "changing its mind" behavior users report from machine learning. Speed is paramount; checks complete in under 10 milliseconds, a direct benefit of local processing and zero network latency.

Harper's credibility is further solidified by Automattic, the company behind WordPress, which acquired its creator in November 2024. Despite corporate backing, the project remains fully open-source, governed by the permissive Apache 2.0 license. This commitment ensures Harper's continued development and accessibility, free from proprietary lock-in.

Harper differentiates itself with a killer feature for developers: intelligently checking spelling and grammar inside code comments while completely ignoring the surrounding code. This crucial distinction means your documentation, commit messages, and internal notes receive the same rigorous review as prose, without false positives from syntax. It flags typos across virtually every language you write in, a significant advantage for developer workflows.

Integrations are seamless, embedding Harper directly into your daily processes. Developers benefit from native support in popular editors and tools, including: - VS Code - Neovim - Zed - Obsidian

A WebAssembly-powered web demo at write.harper.com also offers a zero-install test drive, running the full checker within your browser tab. This ensures broad accessibility and ease of adoption.

Cloud-based tools like Grammarly, despite their broader reach (for more on their offerings, see Grammarly: Free Online Writing Assistant), often stumble here. They frequently misinterpret code fences and developer-specific syntax, leading to frustrating errors or missed corrections. Harper’s local, rule-based engine sidesteps these issues entirely, providing reliable checks where other tools falter and ensuring your sensitive code never leaves your machine.

Harper's rule-based engine, while fast and private, carries inherent limitations. It currently supports English only, and its approximately 287 handwritten Rust rules offer less comprehensive coverage than competitors. This can lead to missed nuanced errors where no rule applies, or occasional false positives, such as flagging "Cloudflare" in earlier versions. The trade-off for privacy and speed is narrower linguistic scope.

Where Grammarly maintains a distinct edge is its advanced, AI-powered features. These capabilities extend beyond basic grammar and spelling, offering sophisticated assistance like tone analysis, clarity coaching, and full-sentence rewrites. Harper, by design, makes no attempt to replicate these machine learning-driven contextual suggestions, focusing instead on deterministic, local checks.

For developers, Harper is the unbeatable choice. Its free, offline, and privacy-first design provides instant, secure checks for code comments, commit messages, and documentation, ensuring your intellectual property never leaves your machine. Conversely, writers prioritizing advanced AI-driven feedback—like comprehensive rewrites and tone adjustments—will find Grammarly’s subscription service indispensable. If your workflow demands robust AI coaching, Harper isn't your solution; for private, lightning-fast technical text validation, nothing else compares.

What is Harper?

Harper is a free, open-source grammar and spell checker written in Rust. It processes text locally on your device for maximum privacy and speed, making it a popular Grammarly alternative, especially for developers.

How is Harper different from Grammarly?

Harper is free, works offline, and uses a deterministic rule-based engine for consistent results. Grammarly is a paid subscription service that uses cloud-based AI, offering advanced features like tone analysis but sending your data to its servers.

Does Harper work with my code editor?

Yes, Harper is designed for developers. It has official extensions for VS Code and Obsidian, and its language server allows it to integrate with Neovim, Zed, Helix, and Emacs.

Who owns Harper?

Harper was acquired by Automattic, the company behind WordPress, in late 2024. Despite the acquisition, it remains a free and open-source project under the Apache 2.0 license.