File Format Identifier

Identify unknown file types online by analyzing magic bytes. Detect true file format regardless of extension. Find MIME type, correct extension, and file signature.

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How File Format Identifier Works

Every file begins with a unique sequence of bytes called a "magic number" or file signature. PDF files start with %PDF (hex: 25 50 44 46), JPEG images begin with FF D8 FF, and ZIP archives start with PK (50 4B). Our tool reads these first bytes to determine the actual file type, regardless of what extension the file has.

Analysis happens entirely in your browser—files are not uploaded to any server. We read just the first 64 bytes needed for identification, making detection instant even for large files. The tool compares these bytes against a database of 50+ known file signatures.

Why Identify File Formats?

File extensions can be changed, removed, or corrupted. A file named "document.pdf" might actually be an image or executable. Email attachments, downloads from unknown sources, and files without extensions all benefit from format verification before opening.

Developers and system administrators use format identification to validate uploads, detect disguised malware, and troubleshoot files that won't open. Knowing the true MIME type helps select the right application or conversion tool.

Supported Formats

CategoryFormats Detected
DocumentsPDF, DOC, DOCX, XLS, XLSX, PPT, PPTX, RTF, ODT
ImagesJPEG, PNG, GIF, BMP, TIFF, WebP, ICO, SVG
AudioMP3, WAV, FLAC, OGG, AAC, M4A
VideoMP4, AVI, MKV, MOV, WebM, FLV
ArchivesZIP, RAR, 7Z, TAR, GZIP, BZIP2, XZ

Key Features

  • Instant detection by reading file signature (magic bytes)
  • Identifies 50+ common file formats across all categories
  • Detects extension mismatches and suggests correct extension
  • Shows MIME type for web and programming use
  • Browser-based analysis—your files stay on your device

Common Use Cases

Verify downloaded files before opening them. A file claiming to be a PDF document might actually be an executable. Checking the magic bytes reveals the true format regardless of the filename or extension.

Recover files with missing or incorrect extensions. When files lose their extensions or get renamed incorrectly, this tool identifies them so you can restore the proper extension and open them with the right application.

Developers validate file uploads by checking magic bytes server-side. This tool helps test and understand the signatures used for validation. System administrators investigate suspicious files without executing them.

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File Format Identification FAQ

What are magic bytes?

Magic bytes (also called file signatures) are specific byte sequences at the beginning of a file that identify its format. For example, all JPEG files start with bytes FF D8 FF, and all PDF files start with %PDF (hex: 25 50 44 46). This allows reliable format detection regardless of the file extension.

Can I identify a file without an extension?

Yes, that's exactly what this tool is for. Magic bytes are embedded in the file itself, not in the filename. Upload any file—with or without an extension—and the tool will detect its actual format based on the file content.

Why does my file show as "ZIP Archive / Office Open XML"?

Modern Office documents (DOCX, XLSX, PPTX) are actually ZIP archives containing XML files. They share the same magic bytes (PK or 50 4B). To distinguish between them, you'd need to examine the archive contents. The tool shows both possibilities for accuracy.

Is my file uploaded to your server?

No. File analysis happens entirely in your browser using JavaScript. Only the first 64 bytes are read locally to detect the signature. Your files never leave your device. We only send anonymous analytics about detected formats to improve the tool.

What if the format isn't detected?

If the tool shows "Unknown format", it means the file signature doesn't match our database of 50+ known formats. The tool displays the first bytes so you can research the signature manually. Less common or proprietary formats may not be recognized.

Can this detect if a file is safe to open?

This tool identifies the file format, not its safety. It can reveal if an "image.jpg" is actually an executable (EXE), which is a red flag. However, a correctly identified format doesn't guarantee the file is safe—malicious content can exist within legitimate formats. Always scan downloads with antivirus software.

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File Format Identifier | File Converter Lab