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Free AI Watermark Detector

Compare your original text with a rewritten version. See how much of the wording changed and which claims may differ. You can also create a rewrite directly from the original.

Measures rewrite depth between two texts. Vendor watermark keys for Claude and Gemini stay private; see the reference SynthID experiment.

What a text watermark comparison shows

Statistical text watermarks live in the sequence of words a model chose. A rewrite that replaces most five-word sequences leaves that sequence behind. This page measures exactly that: how much of the wording changed between two versions, with a diff and a meaning check. Vendor detectors for Claude and Gemini remain private, so the measure is rewrite depth, not a vendor verdict.

Compare a rewrite or create one

Paste the original in the first box and your rewrite in the second, then select Compare texts. If you only have the original, select Remove watermark. The tool puts a deep rewrite in the second box and shows the same comparison measures.

Read the research behind the approach

I tested rewrite methods against a reference SynthID Text watermark and published the data, examples and limitations. Rewrite depth measures overlap in five-word sequences and is useful for comparing versions.

Read Anthropic's detector access guidance, Google's SynthID overview and the published reference code. My AI text watermark guide explains the distinction between watermarking and AI-style detection.

Questions about the AI Watermark Detector

Can this detect a Claude or Gemini text watermark?

It measures how far a rewrite moved away from the original wording, which is what statistical watermarks depend on. Claude's and Gemini's own detectors need private keys, so this page reports rewrite depth and a diff instead of a vendor verdict.

What does the percentage mean?

It is the share of the result's five-word sequences that do not occur in the source. It measures literal rewrite depth. It is not the percentage of AI writing or of a watermark removed.

What happens when I select Remove watermark?

The original is sent to the Watermark Remover. The rewritten text appears in the second box with a diff and source checks. Creating that rewrite uses one free-trial or purchased rewrite; the comparison itself does not.

Does comparing two existing texts use a run?

No purchased rewrite is used. Compare texts is free and counts toward the separate limit of 100 detector checks per UTC day. Reading an existing result does not use another check.

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Updated 2026-09-13.