Free Google Docs™ add-on

Google Docs AI Detector and Plagiarism Checker

A free add-on that checks your document — or just a selection — for AI writing and plagiarism, highlights matches in place, and inserts citations in 14 styles.

Install from Google Workspace Marketplace
  • Free to install
  • Reads only the open document
  • Text sent only when you click Check
Google Docs AI detector and plagiarism checker sidebar showing 32% plagiarism and 64% AI content, with five matches from three sources highlighted in pink in the essay
40-second demo

Check a Google Doc for AI and plagiarism

Check the whole document, see matches and AI passages highlighted, leave out quotes and references, and add a citation.

How it works

How to check a Google Doc without leaving it

  1. Open the sidebar

    In your document, choose Extensions › Plagiarism Checker Plus › Check this document.

  2. Connect your account

    Sign in once with your free account. The website opens in a small window to confirm.

  3. Choose what to check

    Whole document or a selection; plagiarism, AI or both; with or without quotes and references.

  4. Review and highlight

    Read scores and sources, jump to any match, and highlight matches or AI sentences in the doc.

Scores and sources

Plagiarism and AI scores, highlighted in your document

Everything happens in a sidebar next to your writing, so you go straight from the score to the passages that need attention.

  • Plagiarism % and AI content % in two tabs
  • Matches grouped by source website
  • Click any match to select it in your document
  • Highlight every match; Clear restores your own colours
The add-on sidebar after checking 812 words: Plagiarism 32% and AI content 64% tabs, “Significant similarity · 5 matches from 3 sources”, a Highlight matches in document option, and sources grouped by website with example-journal.org at 25%
Match details

See exactly where each match comes from

Expand any match to compare your sentence with the source, then decide whether it needs quotation marks, a citation or a rewrite.

  • The source paragraph with matching words marked
  • Open source visits the page; Cite builds a citation
  • Group matches by source or in document order
A plagiarism match expanded in the Google Docs sidebar, showing the source paragraph with the matching words marked, Open source and Cite links, and the matched sentence selected in the document
AI detection

Find the passages that read as AI-generated

Instead of a single number, the AI content tab shows which parts of your document drove the score, so you can reread them and put them in your own words.

  • Flagged sentences grouped into passages by paragraph
  • Each passage rated Highly likely, Likely or Possible
  • Shade AI sentences in yellow, or jump to any passage
The AI content tab of the add-on grouping flagged sentences into passages rated Highly likely and Likely, with AI sentences highlighted in yellow in the Google Doc
Citations and exclusions

Cite sources and keep quotes out of the check

Pick from 14 citation styles, including APA 7, MLA 9, Chicago 17, Harvard, IEEE, Vancouver and more. Start a citation from any match, or from the sidebar header.

  • Look up a web page, DOI or ISBN, then Insert at cursor
  • Add to references keeps the list sorted, with a hanging indent
  • Excluded quotes and references aren’t sent, checked or counted
  • Changed the document? The sidebar offers Re-check
The Cite a source panel in Google Docs with an APA 7th citation, Insert at cursor and Add to references buttons, and options to exclude quoted text and the reference list from the check
No detector is perfect
AI detection gives a likelihood — Highly likely, Likely or Possible — not proof. It can flag human writing, especially formal or formulaic text, and miss AI text that has been heavily edited. Treat every result as a starting point for review, not a verdict.
Permissions, explained

What the add-on can and can’t access

Google asks you to allow three permissions when you install. Here is what each one is for.

View and manage the document it’s opened in

To read the text you check, find quotes and the reference list you exclude, and — only when you ask — highlight matches or insert a citation. Never your other documents or your Drive.
documents.currentonly

Display and run its sidebar in Google Docs

To show the sidebar where you choose what to check and read your results.
script.container.ui

Connect to an external service

To send the text you chose to app.plagiarismcheckerplus.com when you click Check, and fetch your results, account and citations. It connects to no other site.
script.external_request
What it can’t do: open your other documents, browse your Google Drive, read your Gmail, or see your Google account profile. It writes to your document only when you ask — to highlight matches or insert a citation.
Privacy

Your document stays yours

How Plagiarism Checker Plus handles your document. Full details are in section 6 of our privacy policy.

Sent only when you click Check

The add-on reads the open document to count words and find what you can exclude. Only the part you chose is sent, and only when you click Check.

Never sold, never used to train AI

Text you check is used only to produce your results. Our use of information from Google APIs follows the Google API Services User Data Policy, including the Limited Use requirements.

You can remove it any time

Delete checks from your history, sign out to remove the token, uninstall from Extensions › Add-ons › Manage add-ons, or revoke access at myaccount.google.com/permissions.

Your sign-in token and a summary of your last check for each document are stored in your own Apps Script user properties. Source website icons come from Google’s public favicon service, which receives only the source website’s domain.

Also for Chrome™

Writing outside Google Docs? Get the Chrome extension.

A Check button in text boxes across the web, checks on text you highlight, and citations for the page you are reading — all from Chrome’s side panel.

The Plagiarism Checker Plus Check button in a text box on a web page, with the Chrome side panel open
FAQ

Google Docs add-on questions

Install the add-on, open your document and choose Extensions › Plagiarism Checker Plus › Check this document. Connect your free account once, choose Whole document or Selection, tick AI detection and click Check. The AI content tab shows your AI score and passages rated Highly likely, Likely or Possible, which you can highlight in the document.

Check your Google Doc before you submit

Plagiarism and AI detection, highlights in your document, and citations in 14 styles. Connect a free account to start, or see plans when you need more words.

Google Docs and Chrome are trademarks of Google LLC. Plagiarism Checker Plus is not affiliated with or endorsed by Google. Plagiarism Checker Plus for Google Docs is provided under our Terms of Service and Privacy Policy. Questions? Contact us.