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File Magic Byte Detector

Upload any file to instantly detect its true file type by analyzing the magic bytes (file signature / header) - regardless of the file extension. The File Magic Byte Detector reads the first bytes of your file and compares them against a database of 120+ known signatures covering images, audio, video, documents, archives, executables, fonts, certificates, disk images, and more. See the hex dump with matching bytes highlighted, the ASCII interpretation, MIME type, file category, and an extension match check that flags when a file's declared extension doesn't match its actual content. All processing runs locally in your browser - no uploads, no signup, completely free.

File Magic Byte Detector

Upload any file to detect its true file type by reading the magic bytes (file signature / file header). The tool bypasses incorrect file extensions and reveals the real format. Shows the hex signature, ASCII interpretation, and whether the extension matches the detected format.

Drop any file here or click to browse

Supports all file types - only the first 64 bytes are read

Features

Magic Byte Signatures

Reads the first bytes of any file to identify its true format using a database of 120+ file signatures covering images, audio, video, documents, archives, executables, fonts, certificates, disk images, and more.

Hex & ASCII Dump

Displays the raw hex bytes alongside their ASCII interpretation, with matching signature bytes highlighted in color. See exactly what bytes identify your file format at a glance.

Extension vs Magic Byte Comparison

Compares the file's declared extension against the detected magic bytes to reveal mismatches. Instantly identifies renamed files, incorrect extensions, and potential security risks.

Multi-Format Detection

Detects nested formats and container formats - identifies WebP inside RIFF, MPEG-4 subtypes (MP4, HEIC, AVIF, 3GP) via ftyp boxes, and ZIP subtypes (DOCX, XLSX, JAR, APK, EPUB) by extension context.

Use Cases

Security & Malware Analysis

Detect files disguised with misleading extensions - a malware executable renamed to .pdf or .jpg. The magic byte detector immediately reveals the true file type, bypassing the extension trick.

File Recovery & Forensics

When recovering files from corrupted media or raw disk images, use magic bytes to identify file types of recovered fragments without relying on file names or extensions.

Debugging File Upload Issues

When a file upload fails or a server rejects a file, check whether the file has correct magic bytes matching its extension. Many upload validators check magic bytes server-side.

Unknown File Identification

Found a file with no extension or an unfamiliar extension? Upload it to the magic byte detector to identify the format by its signature bytes, even if the filename gives no clues.

Data Integrity Verification

Verify that exported or downloaded files have not been corrupted by confirming their magic bytes match the expected format. A missing or wrong signature indicates a corrupt file.

Cross-Platform File Compatibility

When transferring files between operating systems, verify that the magic bytes are intact and correct. Different platforms handle file extensions differently - magic bytes are universal.

About

What Are Magic Bytes?

Magic bytes (also called file signatures, magic numbers, or file headers) are a sequence of bytes at the beginning of a file that uniquely identify its format. For example, every valid JPEG file starts with FF D8 FF, and every PNG begins with 89 50 4E 47. These signatures are defined by the format specification and are checked by operating systems, browsers, and file utilities to determine how to process a file.

Why Magic Bytes Over File Extensions?

File extensions (.pdf, .jpg) are just part of the filename and can be easily changed - a malware author can rename a .exe to .pdf. Magic bytes cannot be easily faked because the file must actually contain valid format structures. Operating systems like Linux's file command and macOS's UTI system rely on magic bytes rather than extensions for type detection.

Where Are Magic Bytes Defined?

Magic bytes are defined in the official format specification documents (RFCs, ISO standards, vendor documentation). The database in this tool covers 120+ signatures from IANA-registered MIME types, common file format specifications, and well-known application formats. Sources include the Linux magic database (man 5 magic), the FreeDesktop.org shared MIME info database, and format-specific documentation.

Browser-Based Processing & Privacy

All file analysis runs entirely in your browser using the File API and Uint8Array operations. Your files never leave your device - no uploads, no server requests, no third-party services. This makes the tool suitable for analyzing sensitive files including proprietary data, security research samples, and personal documents.

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FAQ
What is a file magic byte detector?
A file magic byte detector reads the first bytes of any file and compares them against a database of known file signatures (magic bytes). This reveals the true file format regardless of the file's extension, allowing you to identify renamed files, detect disguised malware, and identify unknown file types.
How many file signatures does this tool support?
The database contains over 120 file signatures covering 16 categories: images (JPEG, PNG, GIF, WebP, BMP, TIFF, AVIF, HEIC, PSD, RAW formats), audio (MP3, WAV, FLAC, OGG, AAC, MIDI, AIFF, WMA), video (MP4, WebM, AVI, WMV, FLV, MKV, 3GP), documents (PDF, DOCX, XLSX, PPTX, RTF, ODF), archives (ZIP, RAR, 7z, TAR, GZIP, BZIP2, XZ, ZSTD), executables (ELF, PE, Mach-O), fonts (TTF, OTF, WOFF, WOFF2), certificates (PEM, DER, PKCS7), disk images (DMG, ISO, VHD), and more.
Can this tool detect any file type?
The tool can detect any file type whose signature is in the database. For files without known signatures, the tool reports them as unknown and shows the raw hex dump for manual inspection. You can use the hex dump to research the unknown signature online.
Does the file get uploaded to a server?
No. The File Magic Byte Detector processes everything locally in your browser. Your files never leave your device - no server upload, no data logging, no third-party requests. Only the first 64 bytes are read for detection.
What is the difference between magic bytes and file extensions?
File extensions are just part of the filename and can be changed arbitrarily. Magic bytes are embedded in the file's binary data by the application that created it and can only be changed by rewriting the file in a different format. Magic bytes are the authoritative way to identify file types.
Can a file have multiple matching signatures?
Yes. Some files match multiple signatures. For example, DOCX files are also valid ZIP files (the tool shows both the specific DOCX match and the generic ZIP match). Container formats like RIFF can contain WAV audio, AVI video, or WebP images - the tool detects the container and the content type.
What does hex dump and ASCII dump mean?
The hex dump shows each byte as a two-digit hexadecimal value (00-FF), spaced for readability. The ASCII dump shows the same bytes as characters - printable characters (letters, numbers, punctuation) appear as themselves, while non-printable bytes appear as dots. Together, they give you a complete picture of the file's first bytes.
Can magic bytes be faked?
It is possible to prepend magic bytes of one format to another (polyglot files), but this requires careful construction and is uncommon. For most security purposes, checking magic bytes is a reliable first line of defense. Advanced analysis may require additional file structure validation.
Is this File Magic Byte Detector completely free to use?
Yes - 100% free, forever. No signup, no account, no premium tier, no usage limits, and no ads. Analyze as many files as you need. All processing is done locally in your browser with zero server uploads.