Shortlist · checked Oct 5, 2026
Best AI content detectors
Detectors estimate whether text was machine-written and give probabilities, not proof. Compare credit limits and which plans include an API before relying on one.
- Lowest listed start
- Undetectable AI · $5/mo
- With a free plan
- 3 of 4
- With API access
- 4 of 4
What to compare
- Free credits per month
- Whether results are probabilistic only
- API access and which plan includes it
- Per-scan or per-credit cost
- 01
GPTZero
GPTZero provides AI detection, writing feedback, plagiarism checking, and classroom integrations for educators and writers. The homepage advertises scanning text from major LLMs, advanced scan modes, Google Docs extensions, and writing replay verification.
Best for: Educators, students, and publishers who need AI content detection, authenticity verification, and writing quality tools.
- 02
Originality.ai
Originality.ai is a content checking service that scans text for AI-generated writing and plagiarism using a credit system where one credit covers 100 words.
Best for: Publishers, editors and agencies verifying content authenticity.
- 03
Undetectable AI
Undetectable AI rewrites AI-generated text to read as human and offers AI detection, sold as word-based subscriptions with a small trial allowance.
Best for: Writers wanting to rewrite and check AI-drafted text.
- 04
QuillBot
QuillBot is an AI writing assistant for paraphrasing, grammar checking, summarizing and translating, with a Premium subscription for higher limits.
Best for: Students and writers who paraphrase or polish text and want fewer usage limits.
This is a shortlist, not a ranking by quality. Tools are ordered by fit for the task, and every price, free-tier and API statement comes from the vendor's own pages on the date shown. Where a figure could not be confirmed it is marked as such.
AI content detectors: common questions
What is the best free AI content detector?
GPTZero, Originality.ai, QuillBot have an ongoing free plan in this list. Free plans change and often cap usage, so check the vendor before relying on one.
What is the cheapest paid option?
Undetectable AI has the lowest listed starting price in this list at $5/mo per month. Some prices are quoted for annual billing; each tool's page shows the billing basis.
Which of these have an API?
GPTZero, Originality.ai, Undetectable AI, QuillBot mention API or developer access. Check each vendor for API pricing, which is usually billed separately.