Anthropic launches free browser checker for Claude-marked files

Anthropic has put up a free browser checker at claude.com/check-content that reads a file, looks for the C2PA content credential Claude attaches during generation or editing, and reports what it finds. The tool runs entirely in the browser: "Your file stays on your device. The checker only reads the embedded credential, not the file itself."

Uploads can be images (JPG, PNG, GIF, WEBP, TIFF, HEIC, AVIF, SVG, DNG, JXL), video (MP4, MOV, AVI) or audio (WAV, MP3, M4A, FLAC), up to 100 MB. The underlying marking initiative, the reason there is anything to check for, applies to Claude models launched on or after August 2, 2026 and pairs signed C2PA metadata with an imperceptible text watermark. Provenance metadata itself is attached to a narrower set — Anthropic's help center names .svg, .png, and .jpg.

The page is blunt about what a hit and a miss actually mean. A positive result tells you "the content provided was processed by Claude" but "doesn't tell you anything about its substance." A negative result is weaker still: the signal may have been "removed, or that the content was produced by a model, platform, or feature that does not support marking." The company's own support article adds that a Claude-generated file can lose its mark when text is "heavily edited, paraphrased, translated, or mixed," when outputs are very short, or through "format conversion, re-saving, screenshots, or other means." It sits alongside a small run on our AI detection tracker, which this week logged Pangram flagging four of ten Commonwealth Prize winners as AI.

It lands during a busy stretch on our Anthropic tracker, a day after the company's EFS release for keeping Claude logs inside customer clouds.