Your files stay on your device

MIME and magic byte checker

Compare a file's extension, declared MIME type and actual signature bytes, with a hex preview and polyglot warnings.

Drop a file here, or click to choose one

Any format · up to 50.0 MB · stays on your device
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Drop a file to check its type claims.

The verdict compares three claims: the extension, the MIME type the browser declares, and the signature bytes actually at the front of the file. ZIP-based formats (DOCX, XLSX, PPTX, ODT, JAR, APK, EPUB) are reported as ZIP containers and not looked inside, since reading archive members is how zip bombs run. Text formats have no magic bytes; saying so is the honest answer. A second signature inside a file is reported as context, because embedded thumbnails are common and innocent, not as a finding. This tool checks one file; it is not an upload validator, and no verdict here proves a file is safe to serve.
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Canonical HTML: https://nutter.tools/files/mime-magic-byte-checker
Markdown version: https://nutter.tools/files/mime-magic-byte-checker.md
Plain-text version: https://nutter.tools/files/mime-magic-byte-checker.txt
Agent index: https://nutter.tools/llms.txt