If you write for a living — or just write a lot of email — you have probably installed more than one AI writing assistant and still wondered which one actually earns its place. The four names that come up most often are Grammarly, QuillBot, ProWritingAid, and Wordtune. They look similar on a pricing page but they solve different problems, and picking wrong means paying for features you will never open.

This guide is a head-to-head comparison of all four. For a wider survey of the category, see our Best AI Writing Tools 2026 roundup. Here we stay focused on the decision: which assistant should you actually keep.

Quick picks at a glance

How we evaluate

We compare each assistant across six dimensions rather than running a single artificial test: (1) accuracy of grammar and clarity corrections, (2) rewriting and paraphrasing quality, (3) depth on long-form documents, (4) how widely it follows you across apps, (5) pricing value for the way real people write, and (6) learning curve. Our ratings reflect where each tool is genuinely best, not where its marketing lands. We assess the free tier, the main paid tier, and — where it exists — the lifetime option, because the right plan changes the verdict for some users.

1. Grammarly — best always-on safety net

Grammarly is less a writer than a writing safety net, and that distinction is exactly why it stays installed on millions of machines. Rather than drafting documents from scratch, it sits in the background of nearly every text box — email, docs, social, CMS — and flags grammar, clarity, and tone issues the moment you type.

• Pros: Reliable grammar and clarity fixes; works across every app; tone and rewriting suggestions.
• Cons: Premium needed for best features; can over-edit your voice.
• Price: Free for basic corrections; Pro $12/mo; Business $15/user/mo.
• Skip it if: You mainly need to reshape sentence structure (reach for QuillBot or Wordtune) or you write book-length manuscripts that need structural reports (reach for ProWritingAid).
• → Full profile: Grammarly

2. QuillBot — best for paraphrasing & summarizing

QuillBot made its name as a paraphraser, and paraphrasing remains its sharpest tool. Paste a dense or awkward sentence and it reshapes the structure across several modes — formal, fluent, creative, shorten, expand — rather than simply swapping synonyms. That structural reshaping is what separates it from a thesaurus or a basic rewriter.

• Pros: Solid paraphrasing; grammar and summarizer included; usable free tier.
• Cons: Rewrites can drift meaning; premium required for the best modes.
• Price: Free for basic modes; Premium $9.95/mo.
• Skip it if: You need an always-on checker across every app (Grammarly) or manuscript-depth reports (ProWritingAid).
• → Full profile: QuillBot

3. ProWritingAid — best for long-form & craft

ProWritingAid is a writing editor and style analyzer aimed at long-form writers rather than instant-message polish. Where most checkers stop at grammar and tone, ProWritingAid runs more than 20 dedicated reports — sticky sentences, sentence-length variety, overused words, pacing, dialogue tags — that surface craft-level problems a quick fixer never catches.

• Pros: 20+ deep reports expose issues Grammarly misses; native Scrivener integration; $399 lifetime license avoids recurring fees.
• Cons: English only, no multilingual support; slower than real-time checkers on 10,000+ word documents.
• Price: Free with a 500-word cap per check; Premium $10/mo billed annually; Lifetime $399 one-time.
• Skip it if: You mostly write short emails and social posts (Grammarly or Wordtune are faster) or you need multilingual support (it is English-only).
• → Full profile: ProWritingAid

4. Wordtune — best for rewriting sentences inline

Wordtune, built by AI21 Labs, specializes in sentence-level rewriting rather than full-document generation. You supply the draft and it helps you express the same idea more clearly, more concisely, or in a different register. Select any sentence and it proposes several alternative phrasings, each preserving your original meaning while adjusting clarity, tone, or length.

• Pros: Sentence-level rewrites preserve meaning while improving clarity; one-click casual/formal tone switching plus expand and shorten; Read & Summarize condenses articles, PDFs, and YouTube videos.
• Cons: Free tier limited to 10 rewrites per day; refines existing text rather than generating from a blank prompt; best experience lives inside the Chrome and Edge extension.
• Price: Free (10 rewrites/day); Advanced $6.99/mo billed annually; Unlimited $9.99/mo billed annually.
• Skip it if: You need to generate long drafts from a blank prompt (use ChatGPT or Writer) or an always-on checker across every app (Grammarly).
• → Full profile: Wordtune

Grammarly vs QuillBot vs ProWritingAid vs Wordtune: which to pick

The short version: Grammarly is the default you keep on because it guards every textbox. QuillBot is the utility you open when you need to reshape or summarize source material. ProWritingAid is the diagnostic editor for people writing books and theses. Wordtune is the inline rephraser for polishing sentences and shifting tone on the fly. None is strictly better — they occupy different slots in a writing stack.

How to choose

• Non-native English professional → Start with Grammarly for always-on correction, add Wordtune when you want sharper phrasing.
• Student rephrasing essays or source material → QuillBot is the paraphraser standard, with a free tier that actually helps.
• Novelist, academic, or long-report writer → ProWritingAid wins on structure reports and the $399 lifetime license pays for itself in roughly three years.
• Busy exec polishing client email → Wordtune or Grammarly for fast, low-friction tone fixes.
• Want one tool to try first → Install Grammarly free; it covers the largest share of daily writing needs.

Related tools & guides

• ChatGPT — for drafting long content that you then polish in a dedicated editor.
• Writer — an enterprise writing assistant for brand-consistent team content.
• Anyword — a performance-focused copywriting assistant with conversion scoring.
• Paperpal — an academic writing and language editor for research papers.
• Best AI Writing Tools 2026 — the broader category roundup.
• Best AI SEO Content Tools 2026 — assistants tuned for search-friendly drafting.
• How to Write AI Prompts That Work 2026 — get better first drafts before you edit.