You write regularly, not by the word
Pro is a flat $2.99 a month for unlimited rewrites and detections — no credits to track, no tier upgrade when you write more this month.
The short answer
Choose Undetectable AI if you want a wider tool bundle — image detection, plagiarism checking, an SEO writer — in one subscription. Choose Penlify if you write often and want to stop watching a word counter.
You want a broader tool bundle
Undetectable AI publicly offers a humanizer, AI detector, image detector, plagiarism checker, SEO writer, and a Chrome extension across 50+ languages.
Feature and pricing comparison
This comparison avoids inventing accuracy percentages or declaring a universal winner.
| Area | Penlify | Undetectable AI |
|---|---|---|
| Primary workflow | Detect AI-pattern sentences, then rewrite them in the same workspace. | Detect and humanize text, plus a bundle of adjacent writing and content tools. |
| Free tier | 5 rewrites and 3 detections a month, no card required. | Free trial limited to roughly 250 words. |
| Paid pricing | Flat $2.99/mo or $24.99/yr (~$2.08/mo) — unlimited rewrites and detections. | Tiered by word credits: $9.99/mo for 10,000 words up to $209/mo for 380,000 words. |
| Usage cap | None on Pro — rewrite and detect as often as you write. | Every tier is metered by monthly word credits that reset unused. |
| Tool breadth | Humanizer, AI-pattern detector, writing history, account features. | Humanizer, AI detector, image detector, plagiarism checker, SEO content writer, Chrome extension, API access. |
| Language support | English-focused rewriting and detection. | 50+ languages supported, with English cited as the most accurate. |
| Availability | Web workspace and Android app. | Web-based, with a Chrome extension and API. |
| Best fit | Writers who rewrite or check drafts often and want one predictable price. | Users who want a larger tool suite and write in bursts within a word budget. |
Honest tradeoff: Undetectable AI has more tools bundled into one product and supports far more languages. Penlify doesn't try to match that breadth — its case is a single focused workspace with no word-counting, at a lower flat price for anyone writing regularly.
Competitor details checked against Undetectable AI's official product page and pricing page on 28 August 2026. Product features and pricing can change.
Why word credits change how you actually write
A metered plan changes behavior before you notice it. When every rewrite draws down a monthly balance, you start trimming what you check — skipping the second pass on a paragraph, deciding a follow-up email isn't worth the word cost. That's a reasonable tradeoff if you write in occasional bursts and a 10,000-word tier genuinely covers your month.
It stops being reasonable the moment you're a regular writer — students revising every assignment, freelancers rewriting client work daily, anyone who wants to check a draft without doing math first. At that point a credit ceiling isn't a safety net, it's a second thing to manage alongside the actual writing.
Penlify's flat pricing exists for that specific case: one plan, no meter, so checking one more sentence never has a cost attached. The tradeoff is real too — Undetectable AI's broader suite covers jobs Penlify doesn't touch, like image detection or plagiarism checking. If you need those in the same subscription, that breadth is worth paying for.
Common questions
Is Penlify cheaper than Undetectable AI?
For most individual writers, yes. Penlify Pro is a flat $2.99 a month (or $24.99 a year) for unlimited rewrites and detections. Undetectable AI's cheapest paid tier is $9.99 a month and caps you at 10,000 words, with higher tiers costing more as your word count grows.
Does Undetectable AI have more features than Penlify?
In tool count, yes. Undetectable AI bundles an image detector, plagiarism checker, SEO content writer, and a Chrome extension alongside its humanizer and detector. Penlify stays narrower: rewriting and AI-pattern detection in one workspace, without the extra tools.
Does Penlify have word limits like Undetectable AI?
No. Penlify's free plan is capped at 5 rewrites and 3 detections a month, but Pro removes both caps entirely for a flat price. Undetectable AI's plans are metered by word count at every tier, including its most expensive one.
Test the workflow with your own draft
Start with the private analyzer. It gives value without requiring an account or sending the text to Penlify.