File Doctor
Universal file identifier with 300+ signatures. Metadata, security, and repair diagnostics.
Choose any file or drag & drop
300+ formats supported • 100% local analysis • No upload
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Secure & Private: All processing happens locally in your browser. Your file never leaves your device.
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❓ Frequently Asked Questions
How does File Doctor identify files?
File Doctor reads the "magic bytes" (file signature) at the beginning of the file, which is the most reliable way to determine a file's true format, regardless of its extension. Our database contains 300+ signatures.
Is my file uploaded to any server?
Absolutely not. All analysis happens locally within your browser using JavaScript. Your files never leave your device.
Does it work with very large files?
Yes. File Doctor uses smart slicing to read only the necessary bytes from the file, so it works efficiently even with files larger than 5GB.
What if the file extension is wrong?
File Doctor will detect the mismatch between the file's actual signature and its extension, alerting you that the file may have been renamed incorrectly.
Can it detect corrupted files?
Yes. If a file has a known extension but lacks the required magic bytes or is unusually small, File Doctor will flag it as potentially corrupted or incomplete.
What metadata can it extract?
File Doctor extracts image dimensions, PDF page counts, audio/video properties, archive contents, font information, and more — all without uploading the file.