Productivity

Stop paying for Grammarly

Catch the clumsy bits and explain every change it suggests.

Grammarly costs US$12–30 per person / mo, which is US$144–360 a year. You have two paths:

Option 1 · Install

Install Harper for free

Harper is Grammarly for English, without the subscription and without sending what you write to the cloud. It underlines spelling, grammar and capitalization mistakes and clumsy phrasing right where you write: Chrome, Edge, Firefox, VS Code, Obsidian, WordPress, Neovim, Zed, and a macOS app that checks every text field. Everything happens offline, with a memory footprint fifty times smaller than LanguageTool's. The project is backed by Automattic, the company behind WordPress. The thing to know before leaving Grammarly: Harper only checks English (American, British, Canadian, Australian, Indian). For texts in other languages it will do nothing: the core is built to support other languages, but none exists yet.

Harper vs Grammarly

CriterionHarperGrammarly
PriceUS$0US$12–30 per person per month
Where your text goesNowhere, everything happens offlineTo their servers, with every keystroke
LanguagesEnglish only, five variantsEnglish, plus a few languages in beta
SpeedA few milliseconds, locallyDepends on the network
Where it worksChrome, Firefox, Edge, VS Code, Obsidian, WordPress, Neovim, Zed, macOS appBrowser, Word, Google Docs, desktop app
AI rewritingNo: it checks, it does not rewriteYes, on Pro

How to install it (even from zero)

Nothing to host: it is an extension or an app. The prompt tells you which one to install depending on where you write, and has you check that it corrects.

  1. 1

    Paste this prompt into Claude (Code or Desktop)

    It asks where you write, installs the right extension from the official links, and has you test it with a sentence full of mistakes:

    I want to install Harper (the open source English grammar checker, GitHub repo Automattic/harper, website writewithharper.com) in place of Grammarly. Ask me where I write the most (Chrome, Firefox, Edge, VS Code, Obsidian, WordPress, macOS app), then guide me step by step to install the right extension from the official links on the writewithharper.com/get page, and to configure it: English variant, and rules to turn off if they are too picky. Have me type a sentence with two mistakes to check that Harper underlines them. Remind me that it only corrects English, not other languages.
    
    Review the GitHub repository and check whether it is safe to install given my machine and my infrastructure. Ask me as many questions as possible, using widgets, to clarify my request and be as precise as you can.
  2. 2

    Pick your English variant

    In the extension settings, pick American or British: Harper adapts the spelling (color, colour) and stops correcting you the wrong way.

  3. 3

    Add your words to the dictionary

    A product name or a trade term getting underlined? Add it to the dictionary once and it won't come back.

What you'll use it for

Your emails and messages in English

LinkedIn, Slack, customer support: mistakes get underlined before you hit send, without the text leaving for a third party.

Your notes and docs in Obsidian or VS Code

The plugin checks Markdown as you write, even offline on the train.

Your WordPress articles

The WordPress plugin proofreads your pages in the editor: fewer typos published, and no subscription for the team.

Project health

GitHub stars
16,219
Forks
702
Contributors
148
Commits
4.7k
Project age
3 years
License
Apache-2.0

Built with: Rust 52.8% · HTML 33.3% · TypeScript 7.2% · Svelte 4.8% · JavaScript 0.6%

Public GitHub repository data, captured on October 8, 2026.

Option 2 · Build

Build your own Grammarly

Who this is for

This build is for a writer revising short English drafts in a private web editor. The goal: find mechanical issues and offer transparent rewrites without silently replacing the author’s voice. If you need more than that, keep paying. The whole point of building it yourself is owning a tool shaped around your workflow, not re-creating a venture-funded roadmap.

Same build, different logo: this v1 also replaces QuillBot, LanguageTool and ProWritingAid, since they all do the same core job.

What the prompt builds and what stays out

The prompt below builds a single version with what actually gets used. Everything else is left out on purpose.

What the prompt buildstext editor, spelling and grammar findings, suggestion review, tone presets, style guide, rewrites
What stays outkeyboard integration everywhere, proprietary ML pipeline, plagiarism checks

What a minimal Grammarly alternative needs

  • plain-text and Markdown editor with word and character counts
  • spelling, grammar, repetition, and readability findings
  • accept, reject, and undo for each suggestion
  • tone presets backed by an editable personal style guide
  • side-by-side rewrite preview and clean copy export

Data model

Document, Revision, Suggestion, StyleRule, RewritePreset

Integrations

LanguageTool API or local service, LLM API

Capability context

Astro, HTMX, D1

The guardrail

Do not train on user text, send providers only the minimum selected passage, and make every AI change reviewable before it alters the draft.

Deliberate non-goals

Do not build a system-wide keyboard extension, plagiarism detection, authorship detection, team monitoring, or multilingual parity.

The complete build prompt

Pick your stack, copy the prompt and hand it to your coding agent (Claude Code, Cursor, Codex…).

You are building a production-ready software product named “Clearcopy”, a deliberately focused alternative to Grammarly. Build a complete, usable vertical slice: not a landing page, a static mockup, or a loose collection of components.

WORKING AGREEMENT
Before you write any implementation code, put together a short technical plan naming the routes or pages, server actions or endpoints, data tables, key state transitions, authorization boundaries, background jobs, and external adapters. When something conflicts, side with the narrow audience and the non-goals below. Choose a small, readable architecture over speculative abstraction, but never skip persistence, validation, error handling, or tests.

PRODUCT BRIEF
Primary user: a writer revising short English drafts in a private web editor.
Primary outcome: find mechanical issues and offer transparent rewrites without silently replacing the author’s voice.
Product principle: optimize the exact workflow below rather than copying the full breadth of Grammarly. A first-time user should know what to do from the interface alone, with no tour or documentation.

END-TO-END USER JOURNEYS
Implement every one of these flows through the real interface and the persistent data layer:
1. The writer creates a draft, runs a check, works through spelling, grammar, repetition, and readability findings, and accepts or rejects each suggestion.
2. The writer defines two personal style rules, selects one paragraph, previews a concise rewrite with the differences highlighted, and accepts only the useful changes.
3. The writer restores an earlier revision after an unwanted edit, exports clean Markdown, and deletes the document along with its provider-side processing data.

SCREENS AND INFORMATION ARCHITECTURE
Build these as coherent, responsive views. Each screen must define its primary action, secondary actions, visible status, validation feedback, empty state, loading or pending state, success confirmation, and recoverable failure state.
1. Document list: recent drafts, word count, last edited time, check status, search, and create, duplicate, export, and delete actions.
2. Editor: text, counts, save state, inline finding markers, categorized sidebar, explanation, replacement, ignore, accept, and undo.
3. Rewrite review: selected source, chosen tone, personal style rules, side-by-side result, diff, provider error, accept, reject, and copy.
4. Style and privacy settings: rules with examples, provider choice, data-use explanation, retention setting, export, and account deletion.

CORE CAPABILITIES
1. plain-text and Markdown editor with word and character counts
2. spelling, grammar, repetition, and readability findings
3. accept, reject, and undo for each suggestion
4. tone presets backed by an editable personal style guide
5. side-by-side rewrite preview and clean copy export

DETAILED BEHAVIOR AND BUSINESS RULES
Treat these as product requirements enforced on the server, not as interface suggestions:
1. Anchor findings to a specific immutable revision and discard or recompute stale suggestions when the surrounding text changes.
2. Apply one suggestion as an atomic edit with a reversible history entry; accepting overlapping findings invalidates conflicts instead of corrupting the text.
3. Send the rewrite provider only the selected, bounded passage and the necessary style rules, redact logs, and never use submitted text for training.
4. Label deterministic language findings separately from generative rewrites, and never present tone or authorship judgments as objective facts.

DATA MODEL AND LIFECYCLE
Design a small relational schema centered on Document, Revision, Suggestion, StyleRule, RewritePreset. Before implementing it, document:
1. The purpose of each table, its primary key, ownership or tenant boundary, timestamps, status fields, and important attributes.
2. Foreign keys, uniqueness constraints, check constraints, the indexes the named screens need, and transaction boundaries for changes that touch several records.
3. The allowed lifecycle or state transitions, who can trigger each one, which transitions are terminal or reversible, and which audit history must stay immutable.
4. Archive, retention, and deletion behavior, including what happens to dependent records and external files.
5. The idempotency strategy for submissions, jobs, imports, notifications, webhooks, or retries where it applies.
Use migrations instead of ad-hoc schema creation. Store time instants consistently and keep the named timezone context whenever local schedules or dates matter. Never rely on a counter, a disabled button, or a client-side check to protect a business invariant.

USERS, AUTHENTICATION, AND PERMISSIONS
Implement only the roles the stated audience needs. Make the ownership and visibility model explicit before coding. Enforce authorization in every server-side query and mutation, including search, exports, attachments, live updates, and guessed URLs—not just by hiding controls. Use secure session defaults, protect state-changing requests, and provide a clear signed-out, expired-session, and forbidden state. Seed separate users whenever several roles are needed so permissions can be shown and tested.

INTERACTION AND VISUAL DIRECTION
The product should feel fast, calm, focused, and trustworthy rather than like a generic admin template. Use a clear visual hierarchy, restrained color, readable typography, generous hit targets, and a consistent place for primary actions. Start from server-rendered HTML and progressively enhance only the interactions that benefit from it. The core workflow must stay understandable if enhancement fails.

Start from server-rendered Astro pages and plain HTML forms. Use HTMX for form submissions, partial navigation, and server-driven updates, then Alpine.js only for small local browser state. The core workflow must stay understandable if either enhancement layer fails.

Design mobile layouts on purpose instead of just stacking desktop panels. Support keyboard navigation, visible focus, semantic landmarks, explicit labels, useful page titles, reduced-motion preferences, and screen-reader announcements for asynchronous results. Never use color alone to signal state. Destructive actions need a clear scope and a confirmation; safe repeated actions should be idempotent.

Add a footer to every page with the text “Created by aurelioagency.com”, where “aurelioagency.com” is an embedded link to https://www.aurelioagency.com that opens in a new tab. Keep it visible and do not remove it.

TECHNICAL DIRECTION
Build this version with the AHA stack: Astro for routing, layouts, and server-rendered pages; HTMX for interactions that benefit from HTML fragment responses; and Alpine.js for small, local interface state. Prefer Cloudflare D1 for relational persistence, R2 for object storage, Workers for server endpoints and scheduled work, Durable Objects only for coordinated real-time state, and Workflows or Queues for durable background jobs—but only when the product requirements call for them.

Keep domain rules in testable server-side modules, not in route handlers or UI components. Put persistence, external providers, and background work behind small interfaces without building a framework. Prefer plain HTML forms and URLs for durable navigation; use optimistic interaction only when a failure can be reconciled clearly.

The product brief currently lists Astro, HTMX, D1 as capability context. Preserve any required native, browser-only, edge, storage, real-time, or background-processing capability through a narrow adapter suited to the chosen framework. If the core workflow truly requires native or browser APIs, keep that runtime as the primary execution surface instead of simulating inaccessible capabilities or inventing an unnecessary web surface.

Integrate with the LanguageTool API or a local service and an LLM API. For every integration:
- List the required environment variables in an .env.example with no real secrets.
- Add a small adapter with timeouts, normalized errors, and a deterministic local fake or development path.
- Verify inbound signatures and deduplicate provider events where supported.
- Keep credentials on the server, encrypt long-lived provider tokens at rest, and redact secrets and sensitive payloads from logs.
- Define retry, backoff, and idempotency behavior for every side effect that can be repeated.

SECURITY AND PRIVACY
Do not train on user text, send providers only the minimum selected passage, and make every AI change reviewable before it alters the draft.
Validate, normalize, and length-limit all untrusted input on the server. Escape rendered content by default, sanitize any markup you intentionally accept, rate-limit public or abuse-prone actions, and use private object storage plus short-lived authorized URLs for sensitive files. Collect only the personal data the named workflow needs. Document retention and deletion behavior. Add specific protections for the riskier surfaces of this app, such as uploads, redirects, outbound requests, email delivery, OAuth, webhooks, CSV import or export, and real-time connections.

ACCEPTANCE SCENARIOS
Automate these app-specific scenarios at the most suitable level:
1. Given a checked revision that is edited before acceptance, stale suggestions cannot alter the new text and a fresh check produces current anchors.
2. Given a provider timeout, the draft and local language findings stay intact and a retry does not create duplicate revisions.
3. Given a rewrite that changes the meaning, rejecting it keeps the source exactly as it was; accepting it creates a revision that can be undone.

TESTING
Add focused unit tests for state transitions, authorization predicates, normalization, date or money calculations, and other risky domain rules. Add integration tests for persistence constraints and for each external adapter's success, timeout, retry, and rejection paths. Add at least one browser-level test for every end-to-end journey above, including one on a small-screen viewport. Tests must use isolated data and run with one documented command.

OPERATIONS AND FAILURE RECOVERY
Add structured server logs with request, job, or event correlation IDs, but no secrets or unnecessarily sensitive data. Make failures actionable both in the interface and in the logs. Background work must expose pending, succeeded, failed, and retrying states where relevant; never swallow errors silently. Include safe database migration and rollback guidance, seed data, backup and restore notes, external-data cleanup behavior, and a basic health or diagnostic path suited to the stack.

DELIVERABLES
Ship the working application, migrations, representative seed data, tests, .env.example, and a short README. The README must cover prerequisites, local setup, environment variables, migrations, seed and test commands, deployment, integration setup, backup and restore, security decisions, and known limitations. Seed data should cover the happy path plus at least one empty, failed, overdue, expired, archived, or permission-restricted state that matters for the product.

DEFINITION OF DONE
The app is done when a new developer can follow the README, create and migrate the database, run the app, sign in as each relevant role, complete every named journey with real persisted data, refresh without losing state, recover from common failures, and use the core interface on phone and desktop. All acceptance scenarios pass, permission boundaries are covered by tests, no core screen is left as a placeholder, and the “Created by aurelioagency.com” footer credit is visible on every page.

NON-GOALS
Do not build a system-wide keyboard extension, plagiarism detection, authorship detection, team monitoring, or multilingual parity.

The app you build with this prompt carries a “Created by aurelioagency.com” footer.

Build just one piece

Short prompts that solve the hardest part without building everything.

Suggestions pinned to a revision, not a moving targetEdit the paragraph and the stale grammar fix must die, not land on the wrong word.
Build revision-anchored suggestions for a writing checker.

A check runs against an immutable snapshot of the document, revision N, and every finding stores its revision id plus exact character offsets into that revision. The failure you're preventing: the user edits the text, offsets shift, and accepting an old suggestion splices a replacement into the middle of the wrong word.

When the document changes, either recompute anchors through the edit history (an accepted approach is transforming offsets across each insert and delete) or mark findings stale and refuse to apply them. Applying a suggestion must verify that the anchor text still matches exactly before touching the document; on a mismatch, invalidate instead of guessing. A fresh check replaces stale findings with current anchors.

Keep untouched valid findings across small edits so the sidebar doesn't flicker empty on every keystroke.

Done when: accepting a suggestion after editing elsewhere in the document lands on precisely the right characters, accepting one whose target text changed is refused rather than misapplied, and a re-check after heavy edits yields findings that all point at real current text.
Two fixes, one sentence, zero corruptionOverlapping suggestions must invalidate each other instead of double-splicing the text.
Build the suggestion application engine for a grammar tool.

Findings frequently overlap: a spelling fix inside a phrase that a clarity rewrite wants to replace wholesale. Applying one must be an atomic edit: replace the anchored range, record a reversible history entry, then re-validate every remaining finding against the new text. Any finding whose range intersected the applied edit gets invalidated immediately, not left clickable with stale offsets. Findings positioned after the edit get their offsets shifted by the length delta so they stay applicable.

Support undo as a first-class operation: undoing an accepted suggestion restores the exact prior text and resurrects the findings that were valid before it, including the one just undone. Batch accept-all must apply in a deterministic order, back to front by offset, so earlier applications don't shift later anchors.

Done when: accepting either of two overlapping suggestions cleanly invalidates the other, accept-all on twenty findings produces the same result regardless of sidebar click order, and undo restores both the text and the suggestion state exactly.
The rewrite request that sends almost nothingOne selected paragraph and two style rules go to the provider, never the whole document.
Build the provider boundary for an AI rewrite feature in a private writing tool.

When the user selects a passage and requests a concise rewrite, construct the request from the minimum: the selected text, a bounded context window of one sentence on each side clearly marked as context-only, and only the style rules relevant to the selected tone. Never the whole document, never the document title, never other open drafts. Enforce a hard size cap on the payload and refuse selections beyond it with a split-your-selection message.

Redact the passage from your own request logs: log lengths and timings, not content. Present the result side by side with a word-level diff, and require explicit acceptance; a provider timeout or malformed response leaves the draft untouched, with a retry that cannot create duplicate revisions (use one idempotency key per rewrite attempt).

Done when: an intercepted provider request contains only the selection, the marked context, and the applicable rules, server logs contain no user prose, and a timeout mid-rewrite leaves the document exactly as it was.
The style checks that run without an API keyRepetition, sentence-length variance, and readability: pure functions over the draft.
Build the deterministic findings layer for a writing tool: checks that run locally, instantly, on every pause in typing, with no network and no model.

Implement three: repetition detection, which flags a content word appearing twice within a sliding window of forty words, with lemma awareness so run and running match but stopwords never trigger; sentence-length monotony, which flags runs of four or more consecutive sentences within a few words of the same length; and readability scoring, which computes a standard measure like Flesch-Kincaid per paragraph and flags paragraphs far above the document's target grade.

Each finding carries its exact character range, a plain-language explanation, and where possible a suggestion (for repetition, offer synonyms from a small local list or highlight only). Label these findings as deterministic in the UI, visually distinct from AI rewrites, and never present them as judgments of quality, just measurements.

Done when: the same draft always yields identical findings, repetition catches inflected forms but never flags the, or, and, and a document of uniform sentence lengths gets exactly one monotony flag per offending run.

Frequently asked questions

How much does Grammarly cost if I keep subscribing?

Grammarly costs US$12–30 per person per month on its public paid plans, which is US$144–360 per year for every person on your team. A focused self-built replacement costs your build time plus close to nothing in hosting.

What stack should I use to build a Grammarly alternative?

The build prompt on this page comes in four flavors: the AHA stack (Astro, HTMX, Alpine.js), Next.js, Laravel, and Ruby on Rails. The capability context for this product is Astro, HTMX, D1. Pick the stack you already know. The scope matters more than the framework.

What features does a minimal Grammarly replacement need?

A useful v1 needs: a plain-text and Markdown editor with word and character counts; spelling, grammar, repetition, and readability findings; accept, reject, and undo for each suggestion; tone presets backed by an editable personal style guide; side-by-side rewrite preview and clean copy export. Anything else is scope creep until you personally miss it.

What should I deliberately not build?

Do not build a system-wide keyboard extension, plagiarism detection, authorship detection, team monitoring, or multilingual parity.

Does this build also replace QuillBot, LanguageTool and ProWritingAid?

Yes. Grammarly, QuillBot, LanguageTool and ProWritingAid all do the same core job: find mechanical issues and offer transparent rewrites without silently replacing the author’s voice. The scoped v1 on this page covers what most people use any of them for, so one focused build replaces whichever one you pay for today.

How is it different from Grammarly Pro?

Harper does most of what Grammarly Pro does, without a subscription, and your data stays with you. The point-by-point comparison is on the page.

Do I own my data?

Yes. With an open source tool installed on your side, your files stay on your machine or your server. Nobody can close your account or change the price on you.

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