Free AI essay checkers that actually work?

I’ve been collecting data on free AI essay checkers because my students keep asking me which one to use to self-check before submitting. Here’s what actually works and what’s a waste of time.

Actually useful (free tier):

GPTZero Free – 10,000 characters/month free. Gives you a percentage score and highlights flagged sentences. Decent accuracy but tends to over-flag. Best for a quick sanity check.

Copyleaks AI Detector – Free tier with limited scans. Uses a different detection method than GPTZero and sometimes catches things GPTZero misses (and vice versa). Worth using as a second opinion.

Sapling AI Detector – Free with no apparent limit (at least I haven’t hit one). Less detailed analysis but very fast. Good for a quick check.

Not worth it (free tier too limited or inaccurate):

ZeroGPT – Wildly inconsistent. I’ve seen it flag the same text as 95% AI one time and 20% AI the next. Don’t trust it.

ContentDetector.ai – Very aggressive false positive rate. Flagged my own hand-written email as 60% AI.

Writer.com AI Detector – Discontinued their free tool, now requires a paid account.

The paid gold standard:

If you need real accuracy and your school doesn’t provide Turnitin access, Originality.ai is worth the small cost ($0.01/100 words). It has the most consistent results in my testing.

My recommendation:

Run your essay through GPTZero AND Copyleaks. If both say you’re fine, you’re probably fine. If either flags you above 20%, review those specific sentences and rework them if needed.

But remember: these tools check for AI-like patterns, not actual AI use. Your perfectly human essay might get flagged, and a cleverly rewritten AI essay might pass. They’re indicators, not proof.

What’s your go-to free checker?