PrePostSEO's AI Content Checker is free, needs no purchase, and sits inside one of the larger free SEO toolboxes on the web. It is also the one tool on their plans page with no plan behind it. That single fact explains most of what it can and cannot do for you, and whether any alternative is worth the switch.
Paste some text or load the example to estimate AI likelihood.
Free tool sites retire and rotate tools without notice, so this was checked first. On 16 August 2026, prepostseo.com/ai-content-detector loaded a working AI checker with a paste area, a live word counter, and a file upload accepting .doc, .docx, .txt and .pdf.
The visible page copy does not state a length limit anywhere. The page's own script does: it sets a constant, MAX_WORD_LIMIT = 2000 (prepostseo.com/ai-content-detector, page source, checked 16 August 2026).
We are reporting the constant, not interpreting it. What the tool does when you exceed it, and whether a logged-in or premium account behaves differently, is not published. The same script also carries an IS_PREMIUM flag, so the page clearly distinguishes account types, but PrePostSEO publishes no document explaining how the AI checker treats them.
The page states that the checker identifies content generated by tools "like Gemini, GPT-5, Gemini 3.0, Grok, DeepSeek, and others", and that it "can also detect content revamped with text spinners or paraphrasers."
Now the part that deserves credit. PrePostSEO publishes no accuracy percentage on this page. No 99 percent, no 99.9 percent, no figure at all. In a category where competitors advertise near-perfect numbers with no methodology attached, declining to invent one is a mark in their favour, and it is worth saying plainly on a page like this.
The naming of specific models is a different kind of claim. Detectors are trained on outputs from models available at training time; a page can list current model names without that list being a tested capability. There is no published evaluation behind it, so read the list as scope of intent rather than measured performance. The same caution applies to any detector, ours included.
The page loads Google's publisher ad tag. That is how the tool is funded.
You want a second opinion, free. Two independent detectors disagreeing on the same paragraph is more informative than one detector agreeing with itself. Running PrePostSEO alongside whatever else you use costs nothing and improves your judgement.
You want a vendor that does not advertise a fake number. If you have grown sceptical of 99.9 percent claims, the absence of one here should count for something.
You need adjacent tools in the same place. PrePostSEO carries hundreds of utilities, from word counters and keyword density checkers to PDF to Word conversion and a WordPress plugin. If your workflow already passes through that site, adding a separate detector vendor buys convenience you do not need.
You want file upload without an account. Dropping a .docx or .pdf straight into a free tool, with no signup, is genuinely useful and not universal.
Your budget is zero and your stakes are low. A blog draft, a client email, a forum post. Pay nothing. Nothing on any paid plan changes the outcome for you.
Free and ad-supported has a shape, and the shape is the same everywhere.
There is no record. Once you close the tab, the check did not happen as far as any system is concerned. There is no export, so what you can show another person is a screenshot. There is no API for the AI checker, so it cannot run inside anything automated. And the 2,000 word ceiling in the code means long documents get chopped into pieces and reassembled by hand.
Whether that matters comes down to one question: does anybody other than you ever need to see the result? If nobody does, none of it matters and you should keep using the free tool.
You want a different free box. SmallSEOTools' AI Content Detector states "Up to 2000 Words will be used", "No charges are associated with using our AI tester", and that it "won't ask you to go through the hassle of getting registered". It advertises "Accuracy 99.9%", a claim with no published methodology, and lists French, German, Portuguese, Spanish, Italian and more (smallseotools.com/ai-content-detector, checked 16 August 2026).
Someone told you to try ContentDetector.ai. That advice has expired. On 16 August 2026 the domain returned an HTTP 301 to moxby.com/marketplace/ai-content-detector, where the detector is a mod inside a browser workspace platform and the listing states the "Pro plan" is required. Moxby's pricing page lists Pro at "$50 per month".
You want detection and rewriting in one place. AI Detector Pro bundles both. Free tier is 3 AI scans a month with 0 humanizations; Basic was listed at "$27.98 $13.99 with 50% off" monthly and Unlimited at "$49.98 $24.99 with 50% off" (aidetector.pro/pricing, checked 16 August 2026). Languages listed: English, Spanish, French, Arabic, German, Portuguese, Korean.
You are buying for a school or university. TraceGPT from PlagiarismCheck.org publishes LMS integrations for Canvas, Moodle, Google Classroom and others, combined plagiarism and AI scanning, OCR input, and prices starting "at $2.08/month", with organisational tiers shown as "Request quote" (plagiarismcheck.org, checked 16 August 2026). No consumer tool substitutes for this.
You want to stay on PrePostSEO but pay for something. Worth knowing: their plans page carries pricing tables for All in One, Plagiarism Checker, Humanizer, Paraphraser, DA PA Checker, Image To Text, Image Translator and Image to Excel. The Humanizer Basic tier was listed at "$7.5 $6.75 /month". The AI Content Detector appears on that page only in navigation, with no pricing table of its own (prepostseo.com/plans, checked 16 August 2026). There is nothing to upgrade the detector to.
TextSight is a paid detector with published prices: Starter $9.99 a month or $7.49 billed annually, Pro $19.99 or $14.99, Business $39.99 or $29.99, Enterprise $79.99 or $59.99. Annual billing is 25 percent cheaper. No discount codes, no struck-through figures.
The box above runs without an account: 3 checks a day, pooled across the AI Detector and the Document Detector, capped at 1,000 words. That ceiling is lower than PrePostSEO's, and it is lower on purpose because the free box is a demonstration rather than the product. Signing up free raises it to 60 checks a day at 5,000 words. Starter gives 200 a day; Pro and above are unlimited. Minimum input is 25 words. Scores read as under 30 "likely human-written", 30 to 69 "mixed signals", 70 and above "likely AI-generated".
What the paid tiers add, in order: sentence-level analysis and PDF export at Starter, Chrome extension and REST API at Pro, teams and branded reports at Business. File upload, URL scan and bulk scan are included across paid use.
The three reasons to move are narrow and specific. You need a dated, exportable record because someone will ask you about it later. You need to check volume, through the API or in bulk, rather than one paste at a time. Or you need to know which sentences drove a score, not just the score. If none of those describe you, the free tool you already have is the correct answer.
TextSight's detector is English-only. It is an ensemble of DeBERTa, RoBERTa and ELECTRA, and it carries a known false-positive bias against writers who learned English as a second language. Simpler syntax, more conventional phrasing and a smaller idiom range all push a score upward, and none of those are evidence of anything.
This is not a quirk of our system, it is a documented weakness of the whole model family, and honest vendors should say so. If a false accusation would cost you a grade, a contract or a job, do not lean on any single detector score, ours very much included. Use it to prompt a conversation, keep your drafts and version history, and never treat a percentage as a finding.
If your work is not in English, PrePostSEO or SmallSEOTools will serve you better than we will.
MAX_WORD_LIMIT = 2000. Treat 2,000 words as the practical working ceiling, and confirm with the vendor if it matters to you.The deeper head-to-head: feature table, where GPTZero wins, where TextSight wins, and migration steps.
Read the comparePerplexity, burstiness, and transformer scoring explained, so you can read any detector's verdict critically.
Read the guideWhy detectors over-flag ESL and formal writing, and how sentence-level evidence helps you defend real work.
Read the guideThe full ranking with detection approach, pricing, and use-case fit side by side.
See the rankingStart with TextSight's free tier. No card, no signup, no commitment. Your first scan in about six seconds, with the evidence shown line by line.
Honest comparisons vs other tools.