Turnitin is a mature academic integrity and grading service that's got an AI writing detection technology to spot AI text. It's got a suite of tools like originality checks, feedback and grading tools to help teachers cope with academic integrity issues. Turnitin is designed to counteract new academic cheating trends like contract cheating and AI text, and it's got tools to help students succeed in different education markets.
Another tool worth looking at is GPTZero. This AI detector is geared specifically to spot text written by large language models like ChatGPT and GPT-4. It's got Deep Scan for more detailed analysis, Source Scanning for plagiarism and AI copyright infringement, and integration with Google Docs through its Origin Chrome Extension. GPTZero is updated continuously through partnerships with leading universities and research labs, so it's got a good track record of staying up to date and spotting new AI tricks.
If you want a simple interface and high detection accuracy, check out AI Detector. You can paste in text and get a report showing the fraction of text written by AI for each sentence. It's good for students, teachers and researchers who need to check authenticity and ensure academic integrity. The tool has a free plan and several paid options, including discounts for schools.