Harper – an open-source alternative to Grammarly

Original Article ↗ Hacker News Discussion ↗

An open‑source grammar checker called Harper is drawing attention as a fast, locally runnable alternative to Grammarly that relies on hand‑crafted rules instead of large language models. Commenters praise its privacy, performance, LSP and editor integrations, and hackability, but note that its current rule set misses many basic errors and lags behind mature tools like Grammarly and LanguageTool in accuracy and polish. The exchange highlights a broader tension between deterministic, rule‑based NLP systems and LLM‑driven tools in terms of consistency, language coverage, ease of evolution, and the kind of writing assistance users actually want.

Architecture & Approach

  • Harper is a rule-based grammar checker written as a classic NLP system, not an LLM.
  • Uses a mix of hard-coded phrase corrections and more dynamic rules (e.g., your/you’re, Oxford comma, other syntactic checks).
  • Some see “decades of NLP research” in the marketing as overstated, given the current code looks like a relatively small, hand-built rule engine without obvious use of older statistical/NLP resources.

Performance, Integrations & UX

  • Key selling point: runs locally, in under ~10ms per document, and can be embedded into apps.
  • Ships with an LSP server; people like it for checking comments in code editors (Neovim, etc.), plus browser extensions including Firefox.
  • One report that the LSP consumed >1 GB RAM in Neovim.
  • Users request: keyboard shortcuts, delay while typing, rule import/export, iOS keyboard, Word and mobile Obsidian support, better Outlook web support, and a stable web demo.

Quality & Coverage

  • Mixed feedback: some find it a “good start” or “decent,” but many note missed basic errors (“Me and Jennifer went…”, “My name John…”, nonsense sentences) and occasional bad suggestions.
  • Several conclude it will need years of rule-writing to get close to Grammarly-level coverage.
  • English-only for now (US/UK/CA/AU variants); broader language support is “on the horizon.”

Comparison to Grammarly, LLMs & Other Tools

  • Many praise the non-LLM design: deterministic, fast, private, and less “AI-bloated” than Grammarly, which multiple users say has become inconsistent, buggy, and overly verbose.
  • Others argue a hand-written rule system is fundamentally inadequate in the age of LLMs; they want an open-source, LLM-based Grammarly clone, especially for multilingual use.
  • LanguageTool and Vale are discussed as existing open-source alternatives; some note Harper’s site should acknowledge that LanguageTool can also run locally.
  • There’s debate about grammar tools in general: some rely on them heavily (dyslexia, non‑native speakers, professionals needing proofreading), while others question why OS/browsers don’t just build this in.

Philosophy & Ownership

  • Long subthread on rule-based vs probabilistic models, language evolution speed, slang, and whether a stable rule set is desirable versus tracking real-time linguistic change.
  • Some distrust Automattic’s long-term stewardship but are reassured by Harper being FOSS and thus forkable.