Pick up any "Grammarly vs ProWritingAid" thread and you'll find the same recycled verdict: Grammarly for polish, ProWritingAid for authors. It's true as far as it goes — but it skips the questions that actually decide which subscription you keep after the trial ends: what does each tool catch, what does it quietly miss, and what does it cost once your real usage shows up?
This is that comparison, updated for August 2026. A disclosure up front: we build AmberPen, a proofreading API for developers, so we spend our working lives measuring grammar checkers against public benchmarks. We have no stake in which consumer app you pick — we don't sell one — and where a tool wins, we say so. At the end we'll cover the case neither product handles, because it happens to be ours.
The short version
- Grammarly is a general-purpose writing assistant: fast, everywhere (browser, desktop, mobile, Office), excellent tone and clarity suggestions, and the strongest "make this email sound confident" feature set. It corrects conservatively.
- ProWritingAid is a writing coach: deeper structural reports, style analysis, pacing and readability scores, and genre-aware feedback aimed at long-form writers — novelists, academics, and content marketers. It corrects more aggressively and explains itself more.
If you write short, practical things — email, Slack, LinkedIn, support replies — Grammarly is the better default. If you write long things — manuscripts, theses, reports — ProWritingAid's reports earn their keep. The rest of this article is the evidence for that summary.
Correction quality: what each tool actually catches
Both tools catch the easy 90% — subject-verb agreement, doubled words, comma splices, common confusables. The differences show up in the remaining 10%, which is where you notice them.
Grammarly plays defense. Its suggestions have a high hit rate: when it underlines something, it's almost always right. The trade-off is recall — it deliberately skips borderline cases to avoid crying wolf. On fluency corrections (rewording an awkward but technically grammatical sentence), it tends to suggest conservative rewrites that preserve your structure.
ProWritingAid plays offense. It flags more — passive voice, adverbs, sentence-length monotony, sticky sentences, vague words — and every flag comes with a rule name and an explanation. The trade-off is noise: a meaningful share of its style suggestions are judgment calls you'll dismiss, and aggressive style rules occasionally push formal writing toward a generic "clean" voice. Writers who accept every suggestion end up with prose that reads like it was written by the tool.
Neither publishes results on standard academic benchmarks like JFLEG or CWEB — both are closed products evaluated by reviewers rather than measured on public corpora. If measured correction quality is your deciding factor, the honest answer is to run your own text through both free tiers for a week and count how many suggestions you accept. Your acceptance rate is the only benchmark that matters for your writing.
The feature that actually separates them: reports vs rewrites
Grammarly's killer feature isn't grammar — it's the tone and clarity layer. It rewrites whole sentences on demand, adjusts formality, and (in the Premium and Business tiers) generates text. The plagiarism checker and the newer AI-detection features live here too. It's an assistant that sits in your workflow and intervenes.
ProWritingAid's killer feature is the report library: twenty-plus analyses — pacing, dialogue tags, repeated words, sentence variety, readability grade, sticky sentences, clichés — that you run over a whole document. A novelist can run the pacing report over a 90,000-word manuscript and see the sagging middle in one chart. Grammarly has nothing comparable; it works sentence by sentence, not document by document.
This is the real fork in the road. Grammarly improves the sentence in front of you. ProWritingAid tells you what's wrong with the document as a whole. Which one you need depends entirely on the length and ambition of what you write.
Pricing, August 2026
| Grammarly | ProWritingAid | |
|---|---|---|
| Free tier | Yes — basic corrections, limited rewrites | Yes — 500 words per check, web editor only |
| Premium entry | $12/month billed annually ($30 monthly) | |
| One-time option | No | Yes — lifetime license (~$399, frequently discounted) |
| Team plans | Business per-seat pricing | Team and academic licensing |
| AI credits | Rewrites/generation capped by plan | Rephrase and critique credits by plan |
Prices are list rates as of August 2026 and both vendors discount aggressively — ProWritingAid in particular runs near-constant sales, and its lifetime license changes the math completely if you plan to use the tool for more than three years. Verify on each vendor's pricing page before you commit; treat this table as a shape, not a quote.
The free tiers deserve a caveat: Grammarly's free tier is genuinely useful for casual writing. ProWritingAid's free tier is a demo — the 500-word cap makes it unusable for the long documents that are its whole reason to exist. If you're evaluating ProWritingAid, evaluate the paid trial on a real manuscript chapter, not the free tier on a blog post.
Integrations: where each one actually works
Grammarly wins on surface area. Browser extension for Chrome, Safari, Edge, Firefox; desktop apps for Windows and Mac that work system-wide; Microsoft Office add-in; Google Docs; mobile keyboards for iOS and Android. If you write somewhere, Grammarly is probably already there. The browser extension is the product for most people.
ProWritingAid covers the same major surfaces — browser extensions, Office, Google Docs, desktop apps — and adds one Grammarly lacks: Scrivener integration, which matters enormously to its novelist base and to no one else. Its Google Docs add-on is noticeably slower than Grammarly's on long documents, and its browser extension occasionally fights with other editors' own checkers.
A practical note for both: either tool's browser extension will conflict with a web app's built-in suggestions or with each other. Run one at a time.
What neither tool does
Both Grammarly and ProWritingAid are closed, consumer-facing products. That's a deliberate design choice, and it creates a hard boundary that matters if your needs drift in certain directions:
- No API for your own product. You cannot send text to either service and render the corrections inside your app. Grammarly operates a developer platform, but its APIs measure writing quality and administer licenses — the Writing Score API returns a numeric score, not corrections; we covered exactly what it does and doesn't return in what Grammarly's API actually offers. ProWritingAid offers no public correction API at all.
- No self-hosting or privacy controls. Your text goes to their servers, under their retention policy, full stop. Grammarly Enterprise and ProWritingAid's team plans add admin controls, but there is no on-premise or region-pinned option for either.
- No offline or air-gapped use. Both require a connection.
- Limited vocabulary control. Both let you build a personal dictionary; neither supports the per-customer, per-document vocabulary overrides a product embedding them would need.
If you hit any of these walls, you're not looking for a better writing assistant — you're looking for a different category of tool: a proofreading API that returns structured corrections your own software renders. That's the category we build in, alongside Sapling, GrammarBot, and self-hosted options like LanguageTool. The grammar checker API comparison covers all seven options with benchmark data, and what you'll actually pay models the per-character billing those APIs use.
Which one should you buy?
Choose Grammarly if you write mostly short, functional prose — email, chat, documents, social posts — and you value speed and convenience over depth. The browser extension plus tone suggestions is the best-in-class experience for everyday writing, and the free tier is enough for many people.
Choose ProWritingAid if you write long-form — novels, academic work, reports, books — and you want to improve as a writer, not just fix today's document. The reports teach you your own habits, the explanations justify every flag, and the lifetime license makes it the cheaper tool over a multi-year horizon.
Choose neither, and look at the API category, if you're a developer building writing features into your own product, you need corrections as structured data rather than a branded UI, or your text can't leave your infrastructure. That's the only one of the three scenarios where we can help directly — you can create a free AmberPen test key and see the edit format in minutes.
Both Grammarly and ProWritingAid offer trials or workable free tiers. Run your own two weeks of real writing through both, count accepted suggestions, and keep the one you actually listen to. The best grammar checker is the one whose advice you take.