Should you build your own Grammarly?
Grammar, clarity, tone, and AI writing assistant across apps
You can build grammar checks and rewrites, but Grammarly's moat is cross-app extensions, inline UX, enterprise controls, writing telemetry, and long-running language quality.
ENOriginal research content in English. Original prompt preserved in English.
Build me a personal writing checker to replace Grammarly. Requirements:
- Grammar engine: LanguageTool running locally via its official Docker image;
grammar checks never leave my machine.
- A local web page (Node + Express, binds to localhost): paste text, see
LanguageTool issues underlined with hover explanations, click a suggestion
to apply it.
- An LLM rewrite pane (key in .env) with three buttons: tighten, friendlier,
formal. Show a diff against my original before I accept anything.
- A personal dictionary file (dictionary.txt) of names and jargon to never
flag, passed to LanguageTool on every check.
- CLI mode: `check <file.md>` prints issues with line numbers, exits nonzero
if any, so it can run as a git pre-commit hook on docs.
- Everything local except the optional LLM call; no accounts, no telemetry.
- Out of scope: a browser extension and inline suggestions inside Gmail,
Docs, or Slack. This is a destination I paste into, that is the honest
trade against Grammarly.
- README: Docker setup for LanguageTool, the roughly 1 GB of RAM it wants,
and where the LLM key goes.The prompt opens pre-filled in your agent. Review it before running. · this prompt is generated from the build plan · improve it via PR
What would building your own look like?
Run text through LanguageTool plus an LLM rewrite/tone checker, expose a browser extension or local editor.
What you will need
- grammar engine/API
- LLM API
- browser extension
- optional desktop accessibility layer
- user dictionary
They pay because suggestions appear inside the apps where writing actually happens.
xinline suggestions everywhere
xdocument/email integrations
xtone/brand controls
xenterprise admin
xpolished false-positive handling
Prefer something ready-made?
HarperA fast English grammar checker that stays on your device and mostly keeps its opinions to itself.Open source↗
Writing ToolsSelect text anywhere, hit a hotkey, and fix, rewrite, summarize, or obey a custom instruction without opening another tab.Open source↗
WritingToolA LibreOffice extension with long-document checks, style statistics, profiles, and local AI; installing Java is the cover charge.Open source↗View all 4 alternatives to Grammarly →· Licença, instalação e limitações em cada alternativa.
How much does Grammarly cost?
- Monthly billing
- $30/mo$30/mo
- Per year
- $360/yr$360/yr
- Annual billing
- $144/yr60% cheaper than paying monthly
- On a Brazilian card, with 3.5% IOF
- R$157/moR$753/yr
Saved to My list. You will see a notice on this site when the price changes.
You complete the purchase on Grammarly’s site. Vibe Radar does not handle payments.
| Plan | Monthly | Annual (per month) | What is included |
|---|---|---|---|
| free | $0/user | $0/user | 100 generative-AI prompts/month. |
| pro | $30/user≈ $30 | $12/user≈ $12 | 2,000 AI prompts/member/month; up to 149 seats; 1 style guide; 1 brand tone; 2 groups. |
| enterprise | custom | - | Unlimited prompts, members, style guides, brand tones, and groups. |
Free tier100 generative-AI prompts/month
Billing termsmonthly + quarterly + annual for Pro; Enterprise is custom
Additional costsAdditional Pro seats are prorated. A 7-day trial is available only for eligible accounts.
verified 2026-10-20 · source ↗
Is it cheaper to build or buy Grammarly?
Adjust the numbers: hours to build, your hourly rate, running costs and the subscription price.
Over 24 months, subscribing is cheaper.
Starting hours estimated from the analysis (multi-day). Does not price what you give up (support, integrations, security).
Can I rebuild Grammarly?
Kinda. The core of Grammarly is buildable in a weekend with the prompt on this page, but there are real gaps: inline suggestions everywhere, document/email integrations. Read the honest list above before committing.
How much does Grammarly cost?
Grammarly costs about $30/mo (Pro, checked 10/20/2026), which is $144 per year.
What do I lose by replacing Grammarly?
Honestly: inline suggestions everywhere; document/email integrations; tone/brand controls; enterprise admin; polished false-positive handling. If any of those are load-bearing for you, keep paying.
Is there an open-source alternative to Grammarly?
Yes: Harper (A fast English grammar checker that stays on your device and mostly keeps its opinions to itself.) Writing Tools (Select text anywhere, hit a hotkey, and fix, rewrite, summarize, or obey a custom instruction without opening another tab.) WritingTool (A LibreOffice extension with long-document checks, style statistics, profiles, and local AI; installing Java is the cover charge.) All 4 curated free alternatives are at https://viberadar.si/grammarly/alternatives. The prompt is for when you want it exactly your way.