AI Detector – Plagiarism Checker Plus by Plagiarism Checker Plus

Free AI detector and plagiarism checker for Firefox, with a citation generator built in. Plagiarism Checker Plus lets you check what you write in any text box, check text you highlight on any page, and cite the page you're reading, all from the Firefox sidebar, without copying and pasting into another tab.

What you can do

• AI detector (AI checker): get an overall AI score and the sentences most likely written by AI tools such as ChatGPT, Claude or Gemini, most likely first, each with its likelihood. The "Your text" view shades them in your own writing.
• Plagiarism checker: see a similarity score, every web source your text matches, and the matching passages.
• Citation generator: cite the page you're on in APA 7, MLA 9, Chicago or Harvard. Edit any detail, copy it with italics intact, or save it to a citation project.
• Sidebar: paste text or send a selection to it, see your word count and what a check will use before you start, and open the full report on our website.
• History: find your recent checks again.

Check text for AI and plagiarism where you write

• Check button: a small "Check" button appears on text boxes once you've written 50+ words, including rich editors such as Gmail. It opens the checker in a small window.
• Check bar: highlight 50+ words on any page and choose Check plagiarism or Check AI.
• Right-click any selection, or press Alt+Shift+P, to send it to the sidebar.
• Long checks keep running in the background; you get a notification when results are ready.

How to use it

1. Pin the extension to the toolbar. Try one free guest check per tool (up to 1,000 words), or sign in for your monthly words.
2. Write or highlight text, then click Check.
3. Review the AI score, sources and flagged sentences, or open the full report.
4. On any source page, open the sidebar and click Cite.

You stay in control

• Text is sent to our servers only when you click Check. Word counts are worked out in your browser.
• Hide the Check button and check bar on any site with one click, or turn them off in settings.
• Password fields are never read.
• We don't sell your text or use it to train AI models. See our privacy policy for details.

A note on results

No AI detection is perfect. An AI score is a likelihood, not proof, and results are a guide to help you review your own work, not proof of misconduct. Always read the matched passages and sources yourself.

Free to install; paid plans add more words per month. Requires Firefox 128 or later.

Gmail is a trademark of Google LLC. ChatGPT, Claude and Gemini are trademarks of their respective owners.