Harper

Offline English grammar checking

WHO USES ITAnyone writing English email, proposals or documentation, especially where drafts must not be sent to an outside server.

Use in the browser

An English grammar checker that runs on your own machine, so what you write never leaves it.

★ 15.4k▲ +14 / 7dlast 14 days · stars per dayhollow = no dataAs of 09-18 15:00 UTC

15,443 stars · checked on GitHub 09-17 03:25 UTC GitHub check 41 h late · incl. +4 observed via GH Archive since then · 7-day +14 observed via GH Archive (as of 09-18 15:00 UTC)

The Harper site showing the grammar checker marking issues in a sentence.

TESIGN TAKE

A practical alternative if you write English email or docs often but do not want another subscription. Its suggestions are restrained enough not to flatten your own voice.

TRY

AT A GLANCE

LICENSE: Apache-2.0
USAGE: Commercial use, redistribution OK. Keep notices; mark changes.
LANGUAGE: Rust
PLATFORM: web
ACTIVITY: last commit 1 day ago (2026-09-16) · latest release [unconfirmed] As of 09-17 03:25 UTC
COMMUNITY: contributors [unconfirmed] · open issues [unconfirmed] · made by: [unconfirmed] Reference time unavailable
SOURCES: GitHub
OPEN SOURCE: YES
FIRST SEEN: 2026-09-17 01:24 UTC
CATEGORY: PRODUCTIVITY

A summary, not legal advice.

WHY IT MATTERS

The author spells out the reasoning in the README: existing checkers were expensive and overbearing, and everything you wrote was sent to their servers. The main alternative needed gigabytes of RAM. Harper runs locally, so there is no network round-trip while you revise.

BUILD FROM THIS

Written in Rust under the Apache-2.0 licence. Because the checking happens locally, it works without a network connection.

WHO IT'S FOR

Anyone writing English email, proposals or documentation, especially where drafts must not be sent to an outside server.

START IN 5 MINUTES

# Paste a sentence at writewithharper.com to see the checks first, then follow the site's guide to connect it to your editor.

CAVEATS

English only — it does not check Korean spelling or grammar.

RECEIPT

FIRST SEEN: 2026-09-17 01:24 UTC
AT SOURCE: 2023-10-22 02:58 UTC
KEPT: 2026-09-18 21:07 UTC
STAR DELTA: +4 ★ / 24h As of 09-18 15:00 UTC
CREATED → FIRST SEEN: 1060d
WHEN FIRST SEEN: 15,439 ★
SOURCES: GitHub

The same facts in machine-readable form — View as Markdown · JSON

SIMILAR TOOLS

Up to five from PRODUCTIVITY by ★ total: edited entries first, then repository cards; this entry is highlighted. Drawn from the same stored snapshot as the rankings — a comparison, not a recommendation. As of 09-18 15:00 UTC

NAME	★ TOTAL	▲ 7d	LICENSE	PLATFORM	LAST PUSH
Hermes AgentSelf-improving personal agent	★ 246k	▲ +298	MITpermissive	linux · macos · windows · android · cli	2026-09-17
HarperOffline English grammar checkingTHIS ENTRY	★ 15.4k	▲ +14	Apache-2.0permissive	web	2026-09-16
immich-app/immichCARD	★ 114k	▲ +70	AGPL-3.0copyleft	—	2026-09-13
stirling-tools/stirling-pdfCARD	★ 91.9k	▲ +52	Licence unconfirmedunconfirmed	—	2026-09-13
sherlock-project/sherlockCARD	★ 91.5k	▲ +72	MITpermissive	—	2026-09-13

TIMELINE

2023-10-22 02:58 UTCRepository created
2026-09-17 01:24 UTCFIRST SEEN BY TESIGN
2026-09-18 21:07 UTCPublished on TESIGN

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