Find heavy sentences, passive voice and unnecessary words. Make your own writing easier to read.
Free manual readability editor. AI editing is paid.
Writing & clarity
Harper
Free optionOpen sourceLocal
Check grammar locally in your editor, browser or command line.
What you can use it for
Check grammar locally in your editor, browser or command line.
- Grammarly-style checks with no account and no data leaving your machine.
- Caught 4 issues incl. 'Their'->'they're', tomorow, dont, 'very very'.
Workflow coverage and comparison notes
Local English spelling and grammar checks instead of paid proofreading features in ProWritingAid or Grammarly. No generative rewrite, plagiarism or full-feature parity. Free open-source, privacy-first grammar checker written in Rust alternative to Grammarly Premium. Harper runs entirely locally on your machine, catching grammatical mistakes and misspelled words with zero telemetry or text transmission. Focuses on developer tools, markdown, and editors rather than general web browser typing.
Before you switch
English only; Missed 'it start' subject-verb agreement in our test No Grammarly generative rewriting or plagiarism checking.
Alternatives to these paid apps
Each comparison covers the workflow described above, rather than every paid feature.
More for the same workflow
See alternatives →
LanguageToolCheck spelling, grammar and writing style in documents and browser text fields.
Basic plan free (browser extension/web editor); Premium adds more checks, paraphrasing and longer texts. Core engine LGPL and self-hostable.
Check writing against configurable style rules from the command line.
Everything (MIT).