Claude AI Text Detector

Paste any text to check if it was written by Claude (Anthropic). Free, instant, no login required. Covers Claude 3, 3.5 Sonnet, 3.7, and Opus 4.

Claude 3.7 & Opus 4 Free Forever 75–86% Accuracy No Login

AI Text Detector

Paste any text — instant results, no login required

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0 words — 30 minimum for reliable results
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Analyzing…

Narrative Academic
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Signal Breakdown tap to expand

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Accuracy note: Browser-based detectors achieve ~70–80% accuracy. Use as a screening tool, not sole evidence of AI use. How it works →

What Makes Claude Writing Detectable

Anthropic trained Claude with heavy epistemic humility and ethical awareness. Four patterns persist across Claude 3, 3.5, 3.7, and Opus 4.

Perspective Balancing

Claude presents multiple viewpoints even when not asked: "On one hand... On the other hand..." more systematically than any other major AI. Anthropic's constitutional AI training drives this compulsive balance.

Hedging Vocabulary Cluster

"I think", "I believe", "It seems", "I'm not certain but" — these appear far more in Claude than ChatGPT. Anthropic trained heavy epistemic humility into every model version.

Ethical Asides

Unprompted safety/ethical considerations appear mid-response. Claude inserts "It's worth considering the ethical implications" even in factual tasks — a signature of Constitutional AI training.

Long Qualified Sentences

Average sentence length 30–45 words with embedded subclauses and qualifiers. Claude writes the longest sentences of any major AI model — a structural pattern that survives editing.

Claude Versions This Covers

Detection works across all Claude versions. Older models score higher as they were less trained to vary writing style.

Claude 2 (~88%) Claude 3 Haiku (~78%) Claude 3 Sonnet (~76%) Claude 3.5 Sonnet (~74%) Claude 3.7 Sonnet (~68%) Opus 4 (~62%)
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Why does Opus 4 score lower? Opus 4 has stronger instruction-following, so it varies vocabulary more effectively. Structural patterns like sentence length and perspective balancing remain detectable.

Accuracy & Limitations

Detection accuracy varies by model version and how much the output has been edited. Here's an honest breakdown:

Unedited Claude 2 / Claude 380–88%
Claude 3.5 / 3.7 Sonnet68–78%
Human-edited Claude output40–60%
Heavily humanized Claude25–45%

Claude Detector FAQ

Yes. Claude 3.7 still produces perspective-balancing, long qualified sentences, and ethical asides. Detection rate is 68–74% on unedited output.
Claude uses heavier epistemic hedging ("I think", "I believe") while ChatGPT uses formal vocabulary spikes ("delve", "meticulous"). Both share sentence burstiness as a signal. Claude scores higher on sentence length; ChatGPT on vocabulary density.
Yes, though Opus 4 scores lower (~62%) because it varies vocabulary more effectively. Structural sentence length and perspective-balancing patterns remain detectable.
Yes, completely free. All detection runs as JavaScript in your browser — no server, no API, no login, no word limits.