Claude watermark guide
Claude Watermark Detector
Anthropic says its watermark can be checked with a key, and said it planned to offer a detection API. Without that detector, a third-party site cannot verify whether Claude’s statistical watermark is present.
Detector versus AI detector
A keyed watermark detector tests a specific signal. Generic AI detectors infer style or patterns and do not have Anthropic’s watermark key.
What you can verify today
You can deterministically inspect Unicode controls, spacing, clipboard residue, and eligible file metadata.
Check your Claude text
Inspect every detectable hidden character locally, then clean only the artifacts you select.
Check Text FreeSources
Published August 2026 · Updated September 1, 2026