Can Claude's Watermark Be Detected? Not Yet — Here's Why
“Not yet” refers to general public access here. Anthropic's official detection API is in private preview for eligible organizations. This website has no access to that detector and cannot give you a Claude provenance verdict.
If you want to inspect formatting characters, use the Claude text cleanup tool. Its report concerns exact character operations, not the statistical mark.
A watermark detector and a classifier answer different questions
A keyed watermark detector looks for a particular signal placed during generation. A third-party classifier guesses from patterns it associates with generated writing. The classifier does not become a reader of Anthropic's watermark just because its output is presented as a verdict.
Neither a character count nor a classifier's conclusion establishes the complete history of a passage. A document can contain your writing, quoted material and assisted edits together. Keep process records rather than treating one tool's response as an authorship certificate.
Why a real mark may not be detected
Anthropic describes several legitimate limitations. Text may have been heavily edited, paraphrased, translated or mixed into other writing. A very short passage may leave too little material for a reliable signal. A file's provenance metadata may have been stripped, or the originating model, feature or file type may not support the relevant marking technique. These limitations concern different mechanisms; file metadata and a text watermark are not the same thing.
The absence of a detected mark does not establish human authorship. It also does not tell you that every editing operation preserved the original meaning. Anthropic’s marking and detection limitations ↗
What access in private preview means
The provider lists eligible regulators, law enforcement, media, fact-checkers, independent researchers, educational organizations and EU civil society groups, and plans to expand access. That list describes provider-controlled eligibility. It does not give this editor permission or the technical ability to run the official detector.
What you can verify yourself
You can inspect an enumerated Unicode character, check where it occurred and compare the before-and-after string. With an appropriate file viewer, you can inspect a supported signed Content Credential. Our own-key experiment, when available, concerns a separately generated test sample and cannot predict Anthropic's result on your draft.
Read the evidence guide for the scope of each observation. Before submitting writing, check the recipient's disclosure policy and retain your original. Formatting cleanup does not settle that policy question.