The bookmark is not broken, the tool moved. Requesting contentdetector.ai on 16 August 2026 returned an HTTP 301 to moxby.com/marketplace/ai-content-detector, a listing on a browser extension platform where the detector is presented as a paid add-on. If you wanted the old free paste box, you now need a different one.
Paste some text or load the example to estimate AI likelihood.
Verified directly from the response headers, checked 16 August 2026:
`` HTTP/2 301 location: https://moxby.com/marketplace/ai-content-detector/ ``
Two hops later the browser lands on a Moxby marketplace page. That page is not a paste box. It is a product listing for what Moxby calls a Mod, and it states that the "Pro plan" is required.
The listing describes the tool as one that "adds a 'AI Scan' to the Doc editor inside Moxby" and "Reviews writing patterns to provide guidance on whether content may sound robotic or AI-written." It notes that "While longer text (100+ words) is ideal", and it is unusually direct about what it will not promise: "We do not make any accuracy claims and the results are for informational purposes only."
Moxby is not a detection company. Its homepage describes a browser extension that lets you "Turn your browser into a customizable AI-powered workspace", built around three things: a chat layer that connects to models including ChatGPT and Claude, Mods that modify or replace the sites you use, and Missions, which are automated workflows with KPI tracking.
Published Moxby pricing, checked the same day: a free tier that can "Install and run free Marketplace Mods", then Plus at "$25 per month" or "$250/year", Pro at "$50 per month" or "$500/year", and Max at "$100 per month" or "$1,000/year".
Note the tension there and check it yourself before paying: the marketplace listing for the AI Content Detector states the Pro plan is required, while the pricing page says the free tier can run free marketplace mods. Whether this specific mod counts as free is not resolvable from the published pages, so ask Moxby rather than assuming.
The practical summary: a single-purpose free web tool has become a component inside a general browser workspace product. If you only ever wanted to paste 400 words and see a number, that is a large change in what you are being asked to adopt.
Following the redirect is genuinely the right call for some readers, and this is not a consolation section.
You already use Moxby, or you were going to. If the browser workspace is something you want anyway, detection inside the Doc editor is better than detection in a separate tab. Tools you have to switch to are tools you skip.
You want checking inside the editor, not after it. The mod adds an "AI Scan" action where the writing happens. That is a meaningfully different workflow from copying a finished draft into a box, and for some writers it is the only one that gets used consistently.
You want a vendor that refuses to claim accuracy. "We do not make any accuracy claims and the results are for informational purposes only" is a rarer sentence in this category than it should be. Several free detectors advertise 99.9 percent with no methodology behind it. If you distrust that, the honest disclaimer is a point in Moxby's favour, not against it.
You want the mod to be one of many. If you are also going to build or install other mods, the platform cost spreads across all of them and the detector is close to free at the margin.
If none of those apply, and you just want a paste box, keep reading.
Both of these were verified live on 16 August 2026 and both still offer AI detection.
SmallSEOTools AI Content Detector. The page states "Up to 2000 Words will be used", that "No charges are associated with using our AI tester", and that "this AI detector won't ask you to go through the hassle of getting registered". It also claims "Accuracy 99.9%", which is an advertised claim with no published methodology, and it lists support for multiple languages including French, German, Portuguese, Spanish and Italian. File upload accepts .txt, .doc, .docx, .odt, .pdf, .rtf and .tex. The page loads Google's publisher ad tag.
PrePostSEO AI Content Detector. The page does not state a word limit in its visible copy; the page's own script sets a MAX_WORD_LIMIT of 2000. Upload accepts .doc, .docx, .txt and .pdf. The copy says the checker identifies content from "GPT-5, Gemini 3.0, Grok, DeepSeek" and content "revamped with text spinners or paraphrasers". No accuracy percentage is published. This page also loads Google's publisher ad tag.
Both are free, both are supported by advertising, and both are inside large tool collections. Neither keeps a record of what you checked, neither gives you an export, and neither publishes how the detection works. For a spot check on a paragraph, that is fine and you should not pay for anything.
AI Detector Pro publishes a free tier of 3 AI scans a month with 0 humanizations, then Basic listed at "$27.98 $13.99 with 50% off" monthly and Unlimited at "$49.98 $24.99 with 50% off" monthly (aidetector.pro/pricing, checked 16 August 2026). It bundles detection with a rewriting tool and lists English, Spanish, French, Arabic, German, Portuguese and Korean.
TraceGPT, from PlagiarismCheck.org, is institutional. Its product page advertises LMS integrations, combined plagiarism and AI scanning, OCR input and prices starting "at $2.08/month", with organisational plans quoted rather than listed (plagiarismcheck.org, checked 16 August 2026).
TextSight is where you are. The box above runs without an account: 3 checks a day anonymously, pooled across the AI Detector and the Document Detector, capped at 1,000 words. A free account gives 60 checks a day at 5,000 words. Starter allows 200 a day and Pro upward is unlimited. Minimum 25 words. Bands are under 30 "likely human-written", 30 to 69 "mixed signals", 70 and above "likely AI-generated".
Paid plans are published: Starter $9.99 a month or $7.49 annually, Pro $19.99 or $14.99, Business $39.99 or $29.99, Enterprise $79.99 or $59.99. Annual is 25 percent off. Sentence-level analysis and PDF export begin at Starter, Chrome extension and REST API at Pro, and teams plus branded reports at Business. File upload, URL scan and bulk scan are included.
The limitation you should weigh: the detector is English-only. It is a DeBERTa, RoBERTa and ELECTRA ensemble with a known false-positive bias against writers who learned English as a second language. If you were using ContentDetector.ai on French or Spanish text, an English-only tool is a downgrade regardless of price, and SmallSEOTools' multilingual list will serve you better even though it is free.
If your checks are occasional, private, and nobody else ever sees the result, pay nothing. A free ad-supported box is the correct tool and there is no honest argument otherwise.
Pay only when one of these becomes true. You need a record of what you checked and when, because a client or a manager may ask later. You need an export that reads as a document rather than a screenshot. You are checking more than 2,000 words at a time, routinely. Or you need the check to happen automatically, through an API or across a batch of files, rather than one paste at a time.
That is the whole list. Anything else is an upsell.
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.