The Claude watermark detector
As of August 2, 2026, Claude marks what it makes. New Claude models embed an invisible statistical watermark in generated text, and images and supported files get C2PA Content Credentials: a cryptographically signed note in the metadata. The trigger was the EU AI Act's Article 50, and Anthropic turned it on globally, no opt-out.
Here's what most articles about it won't tell you plainly. The text watermark works by biasing which words Claude picks, using a key only Anthropic holds. No third party can read it yet. Anthropic says a detection API is coming but it hasn't shipped. So anyone selling you a "Claude text watermark detector" today is selling you a guess.
This page does the honest version. The file check is real: it scans for C2PA credential data in your browser, and your file never leaves your machine. The text check scans for the AI writing patterns that detectors and readers actually flag, clearly labeled as a pattern check, not the watermark. When Anthropic ships the detection API, it gets wired in here.
Straight answer first: nobody outside Anthropic can read the actual text watermark yet. It lives in word-choice statistics and needs Anthropic's private key. Their detection API isn't out. Until it is, this scanner checks the next best thing: the writing patterns AI leans on. I'll wire the real API into this page the day it ships.
What a mark actually proves
Less than you'd think, in both directions. A found watermark proves Claude touched the content at some point. It can't tell full authorship from a light edit of your own writing. And a missing mark proves nothing: a full rewrite removes the text watermark, and a screenshot or social upload strips file metadata clean off. Treat the mark as one signal, not a verdict.
If you write with AI and want the output to stop tripping pattern checks like the one above, that's exactly what my Stop Slop setup fixes. One prompt, permanent.
I post my real AI systems every week. Follow @billenri.md on Instagram to see them running in public. And if you want a tool like this built for your business, that's what I do.