Detect Claude 3 AI text in seconds.
AI Checker spots Claude 3 content with sentence-level accuracy. Free detector for Claude 3 Haiku, Claude 3 Sonnet, Claude 3 Opus, and 2 other Claude 3 variants.
Every major Claude 3 version.
- Claude 3 Haiku
- Claude 3 Sonnet
- Claude 3 Opus
- Claude 3.5 Sonnet
- Claude 4
Harder to detect.
Lightly edited and paraphrased Claude 3 text typically scores 5-15% lower. Heavy human editing reduces confidence further — always review the sentence-level breakdown.
How AI Checker spots Claude 3.
Five fingerprints that Claude 3 leaves behind, even after editing.
- 1Even more pronounced sentence-length variation than Claude 2
- 2Increased use of hedging and conditional framings
- 3Tendency to structure answers as numbered or bulleted insights
- 4Distinctive em-dash usage for emphasis
- 5Subtle preference for British-leaning vocabulary
The Claude 3 fingerprint.
Claude 3 raised the bar for detection difficulty across the industry. The Sonnet and Opus tiers in particular produce text with sentence-length variation indistinguishable from skilled human writers on a single-paragraph basis — burstiness alone is unreliable. AI Checker reaches Claude 3 detection accuracy through a different signal: lexical fingerprint matching against Anthropic's training distribution. Claude 3 has predictable preferences in clause-level construction (frequent em-dash usage, parenthetical reflections, conditional framings like "if we take seriously the idea that...") that persist even under aggressive prompt engineering. The hardest variant to detect is Claude 3.5 Sonnet with explicit "informal blog post" prompting — accuracy drops to roughly 82% on unedited output and lower with paraphrasing. We recommend treating any Claude 3 detection result as a starting point for human review, not a final verdict.
What Claude 3 writing looks like.
The question of authorship has, in some sense, always been complicated — but the past few years have made it considerably more so. When we read a piece of writing today, we're often asking not just who wrote it, but how much of what we're reading was generated, polished, or merely suggested by some assistive system. This is a real shift, and it deserves more careful consideration than it usually gets.
Frequently asked questions
Is Claude 3 detection free?
Yes. AI Checker offers a free tier for detecting Claude 3 text without signup. The free tier supports up to 10,000 characters per check with full sentence-level breakdown.
How accurate is Claude 3 detection?
On unedited Claude 3 output, AI Checker reaches 95-98% accuracy. Accuracy stays above 90% on lightly edited or paraphrased Claude 3 content. Heavy human editing reduces detection confidence — always review the sentence-level breakdown for nuance.
Can Claude 3 be used in a way that avoids detection?
Heavy paraphrasing and manual editing can lower detection scores, but multi-signal detection (perplexity, burstiness, lexical fingerprinting) usually still catches at least one signal. AI Checker reports a probability rather than a verdict — treat scores as evidence, not proof.
Does AI Checker detect all Anthropic models?
Yes. AI Checker is calibrated for every major model from Anthropic, including the latest variants. We retrain on each major release to keep detection signatures current.
Is my submitted text private?
Yes. Text submitted to AI Checker is processed in memory and is not used to train models. We do not sell or share your content. Free tier submissions are not stored beyond the immediate analysis.
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