Side-by-side comparison · Writing & Translation
GPTZero vs Grammarly vs Undetectable AI
Everything that matters when choosing between them, in one place: our rating, what each can do, what they cost, and the trade-offs.
Comparing 3 tools, the maximum.
At a glance
Pick it if: Teachers, editors and business owners who want a second opinion on whether writing they've been handed came from AI.
Pick it if: Anyone who writes emails, documents and messages at work and wants mistakes caught and tone checked before they hit send.
Pick it if: Marketers and writers who use AI for first drafts and want them to sound less robotic.
Grammarly scores highest overall, but GPTZero gives you more for your money. Which one is right comes down to what you value most.
Overview
| Attribute | GPTZero | Grammarly | Undetectable AI |
|---|---|---|---|
| In one line | Checks whether text was written by AI, with plagiarism and citation checks too. | Fixes grammar, clarity and tone in your writing, wherever you type. | Rewrites AI-written text so it reads more human and is less likely to get flagged. |
| Pricing model | Freemium | Freemium | Freemium |
| Starting price | $0 | $12/member/mo | $0 |
| Free plan | Yes | Yes | Yes |
| Works with Claude Code | Yes | No | Yes |
Rating breakdown
Our scores out of 5. The higher bar in each row is highlighted.
| Attribute | GPTZero | Grammarly | Undetectable AI |
|---|---|---|---|
| Overall rating | 4.2 | 4.3Winner | 3.6 |
| Ease of useHow quickly someone non-technical gets value from it. | 4.5 | 5.0 | 4.0 |
| FeaturesHow completely it covers its own job, and how well the pieces fit together. | 4.5 | 4.5 | 3.5 |
| Output qualityHow good the results are before you fix them. | 3.5 | 4.0 | 3.0 |
| Value for moneyWhat you get for the price, including the free plan. | 4.0 | 3.5 | 3.5 |
| Speed & reliabilityHow fast it is and how often it falls over. | 4.5 | 4.5 | 4.0 |
Feature comparison
A tick means it does this today. A dash means we haven't checked.
| Attribute | GPTZero | Grammarly | Undetectable AI |
|---|---|---|---|
| Access & platform | |||
| Free plan | Yes | Yes | Yes |
| Mobile app | No | Yes | No |
| Desktop app | – | Yes | – |
| Browser extension | Yes | Yes | Yes |
| API access | Yes | – | Yes |
| Teams & business | |||
| Team workspace | Yes | Yes | No |
| Enterprise plan or SSO | Yes | Yes | – |
| Connects to other apps | Yes | Yes | No |
| Open source or self-hosted | No | No | No |
| AI abilities | |||
| Works with your files | Yes | – | Yes |
| Understands images | – | – | Yes |
| Makes images | No | No | No |
| Makes video | No | No | No |
| Writes code | No | No | No |
| Runs agents or automations | No | – | No |
| Learns your brand or style | – | Yes | – |
| Works in many languages | Yes | – | Yes |
| Capabilities score | 8/ 17 | 8/ 17 | 6/ 17 |
Pricing
Plans as listed on each vendor's site when we last checked. Confirm before you buy.
| Attribute | GPTZero | Grammarly | Undetectable AI |
|---|---|---|---|
| Plans | Free $0 Checking the odd document. | Free Free Basic spelling and grammar checks. | Free $0 Testing one short piece. |
PremiumOur pick $23.99/mo, or $12.99/mo billed yearly Teachers and editors checking work every week. | ProOur pick $12/member/mo billed yearly, or about $30 monthly Anyone who writes a lot at work, alone or in a team. | 10K words $9.99/mo, or $5/mo billed yearly ($60) Occasional use. | |
Professional $45.99/mo, or $24.99/mo billed yearly Agencies and heavy users scanning lots of files. | Enterprise Custom Large organisations with security needs. | 20K wordsOur pick $19/mo, or $9.50/mo billed yearly ($114) Regular blog content. | |
Team Professional price per seat, 2 seats minimum Schools and businesses buying for a group. | Larger plans From $31/mo, or $15.75/mo billed yearly Agencies and high volume. | ||
| Which plan to pick | Start on Free. If you check more than a few documents a week, Premium on yearly billing is the sweet spot. Professional only makes sense if you scan big batches of files. | Free is enough for typo-catching. If you write for clients or customers every day, Pro on yearly billing is good value; paying monthly costs more than double. | Test the free 250 words on your own writing first. If the output works for you, a small yearly plan is cheap. Word credits reset monthly, so don't buy more than you use. |
Key features
| Attribute | GPTZero | Grammarly | Undetectable AI |
|---|---|---|---|
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Pros and cons
| Attribute | GPTZero | Grammarly | Undetectable AI |
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Who each one is for
| Attribute | GPTZero | Grammarly | Undetectable AI |
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Questions people ask
Which is better, GPTZero, Grammarly or Undetectable AI?
Grammarly scores highest overall in our ratings (GPTZero 4.2/5, Grammarly 4.3/5 and Undetectable AI 3.6/5). GPTZero is best for checking essays and assignments for AI writing and screening freelance or agency content. Grammarly is best for proofreading emails and documents as you type and checking tone before a tricky message goes out. Undetectable AI is best for Making AI drafts sound less robotic and seeing how detectors might score your text.
Which is cheaper, GPTZero, Grammarly or Undetectable AI?
GPTZero: There's a free plan, and paid plans start at $0. Grammarly: There's a free plan, and paid plans start at $12/member/mo. Undetectable AI: There's a free plan, and paid plans start at $0.
Which is easier to use, GPTZero, Grammarly or Undetectable AI?
Grammarly rates highest for ease of use in our scores. Anyone who writes emails, documents and messages at work and wants mistakes caught and tone checked before they hit send.
How we compare
Ratings are our own, from using each tool, across ease of use, features, output quality, value for money, speed & reliability.
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