Writing and content decision
Grammarly
A single developer can build a useful web-based grammar + rewrite assistant that covers core consumer workflows, but Grammarly’s enterprise-grade compliance, large-scale integrations, and brand trust are durable advantages you won't replicate quickly—so keep paying for full parity.
Visit website↗Open-source builds that already do this
Every project below is open source and already does this job today. Fork one, self-host it, or take the parts you need — the build prompt further down assumes an empty file, and this is the shortcut past that. Licences differ; check the one on each card before you ship.
What a replacement has to do
- Provide inline writing suggestions and full-sentence rewrites by capturing user text client-side, sending it to an LLM backend for grammar/rewrites, and returning annotated suggestions for acceptance.
What it still won’t have
- Enterprise-grade security certifications and compliance assurances (SOC 2, BYOK, DLP)
- Scale and integrations across 1M+ apps and browser ecosystems
- Proprietary plagiarism detection and detector/AI-humanizer tooling
- Brand trust, large user base, and enterprise support SLAs
What remains hard
- Compliance and regulation
Grammarly’s SOC 2 (Type 2) report attests to our enterprise-grade system and organization controls regarding security, privacy, availability, and confidentiality.
- Brand trust
Trusted by 50,000 organizations and 40 million people
First-year cost
Keep paying
Paying is—cheaper in year one.
On cash alone, building overtakes the subscription at 2 seats.
Money you would actually spend
Time you would spend
—
What you would spend
What we assumed
The verdict above measures whether you could build it. This one is only about money.
Runnable build prompt
Build a minimal Grammarly-like web app using React for the frontend, Node.js + Express for the backend, PostgreSQL for user and subscription data, and integrate OpenAI (or similar) for grammar correction and rewrites. Core features in scope: (1) sign-up/login, (2) a web editor showing inline suggestions and full-sentence rewrite actions, (3) backend LLM calls with rate-limiting and fallback rule-based checks, (4) one paid 'Pro' flag in user accounts that unlocks rewrite/tone features, (5) tests for backend endpoints and editor integration, and (6) deployment config (Docker + VPS). Out of scope: browser extension, plagiarism detection, enterprise security certifications, advanced analytics, and multi-app integrations. Include error handling for LLM failures, input validation, logging, and unit/integration tests for critical flows.
How we checked
How the score was reached
- Partly verdict base52
- An open-source build was found+5
- 5 cited sources+3
- Price verified on pricing page+3
- 3/3 assessment runs agreed+4
- Hard moats found in the evidence-3
- Evidence score64
The base comes from the verdict. Everything under it is a check that either happened or did not, and each one is a fact frozen in this record rather than a judgement made at render time — so the same evidence always produces the same number.
How scoring works →Cited sources · 5
Every page the run actually retrieved.
- official productGrammarly: Free AI Writing Assistance Product
- official pricingGrammarly Prices and Plans | Grammarly
- official docsProduct Features | Grammarly Product
- open sourcelanguagetool-org/languagetool
- open sourcetheJayTea/WritingTools
Integrity checks
What held up, and what did not.
