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File Header Analyzer

Upload any file to view and interpret its binary header bytes. The File Header Analyzer reads the first 128 bytes of your file and provides a field-by-field breakdown with plain-English explanations of what each byte means. Supports deep header parsing for PNG (signature + IHDR with dimensions, bit depth, color type), JPEG (SOI, APP0/JFIF, SOF0 markers), PDF (version detection), ZIP (local file header with compression method, CRC-32, sizes), GIF (87a/89a version, screen descriptor), BMP (file + DIB header with width, height, bit depth, compression), and ELF executables (architecture, OS/ABI, file type). See the raw hex dump alongside ASCII interpretation, with expandable field cards showing offset, length, hex value, and interpreted values. All processing runs locally in your browser - no uploads, no signup, completely free.

File Header Analyzer

Upload any file to view and interpret its header bytes. The tool reads the first 128 bytes, identifies the file format from known signatures, and breaks down each header field with descriptions of what it means. Supports PNG, JPEG, PDF, ZIP, GIF, BMP, ELF, and other formats.

Drop any file here or click to browse

Only the first 128 bytes are read - no file upload

Features

Field-by-Field Header Parsing

Breaks down the file header into individual fields - magic bytes, version numbers, dimensions, compression methods, and more. Each field shows offset, length, hex value, ASCII, and a plain-English description of its purpose.

Format-Specific Analysis

Supports deep header parsing for PNG (signature + IHDR), JPEG (SOI, APP0/JFIF, SOF0 markers), PDF (version + binary marker), ZIP (local file header), GIF (screen descriptor), BMP (file + DIB header), and ELF (executable format).

Hex & ASCII Viewer

Displays the raw header bytes as both hexadecimal values and ASCII characters. Color-coded and formatted for easy reading. Copy the hex dump with a single click for further analysis.

100% Browser-Based Processing

All file analysis runs entirely in your browser using the File API. Only the first 128 bytes are read - your files never leave your device. No uploads, no servers, no third-party services involved.

Use Cases

Security Analysis & Malware Detection

Examine file headers to detect malformed headers, polyglot files (files valid in two formats), and files with tampered magic bytes. Security researchers use header analysis to identify suspicious file modifications.

Corrupted File Diagnosis

When a file won't open, analyze the header to determine if the file signature is intact. A missing or corrupted header often explains why software rejects a file, helping you decide if recovery is possible.

File Format Education & Learning

Learn how file formats work at the byte level by exploring real headers. See how the PNG signature detects ASCII transfers, how JPEG markers organize image data, and how ZIP headers track compression metadata.

Unknown File Format Research

When reverse-engineering an unknown file format, start with the header. The hex dump reveals field boundaries, byte ordering (endianness), and padding patterns that help you understand the file structure.

Data Integrity Verification

Verify that exported or downloaded files have intact headers by comparing against known format specifications. A missing or altered signature byte indicates data corruption or truncation during transfer.

File Header Forensics

In digital forensics investigations, header analysis reveals which software created the file, what version was used, and whether the header has been modified. This metadata can be crucial evidence.

About

What Is a File Header?

A file header (also called a file signature or magic number) is a sequence of bytes at the beginning of a file that identifies its format, version, and structure. Headers are defined by file format specifications and contain critical metadata such as dimensions (for images), compression methods (for archives), code entry points (for executables), and color information (for bitmaps). Every valid file format has a specific header structure that tools use to determine how to read and process the file.

How Header Analysis Works

The File Header Analyzer reads the first 128 bytes of any file and compares them against a database of known format descriptors for PNG, JPEG, PDF, ZIP, GIF, BMP, and ELF formats. Each format descriptor defines a matching function (to check if the bytes match) and a parsing function (to extract and interpret each header field). The tool displays fields with their offset, length in bytes, hex value, ASCII representation, and an interpreted value when applicable (e.g., image dimensions, version numbers).

Key Header Fields Explained

Common header fields include: magic bytes (fixed signature identifying the format), version numbers (encoding standard compliance), data offset (where the actual content begins), dimensions (width/height for images and video), compression method (how data is compressed), color depth (bits per pixel), resolution (DPI/PPI for printing), and flags (bit-packed settings for various features). Each field has a specific offset and length defined by the format specification.

Browser-Based & Private

All analysis runs entirely in your browser using the JavaScript File API and Uint8Array operations. Only the first 128 bytes of your file are read - your files never leave your device, no data is uploaded to any server, and no third-party services are involved. This makes the tool suitable for analyzing sensitive files including proprietary data, security samples, and personal documents.

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FAQ
What is a file header analyzer?
A file header analyzer reads and interprets the first bytes of a binary file, displaying each header field with its offset, hex value, ASCII interpretation, and a plain-English explanation. It helps you understand how different file formats are structured at the byte level and can diagnose corrupted files, identify unknown formats, and detect tampered headers.
What file formats does the header analyzer support?
The tool provides deep header parsing for PNG (8-byte signature + IHDR chunk with dimensions, bit depth, color type), JPEG (SOI marker, APP0/JFIF segments with version and density, SOF0 with dimensions), PDF (signature and version), ZIP (local file header with compression method, CRC-32, sizes), GIF (version 87a/89a, screen descriptor), BMP (file header + DIB header with width, height, bit depth, compression), and ELF executables (architecture, OS/ABI, file type). Files that don't match a known format show a raw hex dump.
How many bytes of the file header are analyzed?
The tool reads the first 128 bytes of the file. This is sufficient to capture the complete header for most common file formats - PNG signatures are 8 bytes, JPEG SOI markers are 2 bytes, BMP file headers are 14 bytes, and ZIP local file headers are 30 bytes. The extended analysis (like PNG IHDR chunks or JPEG segment parsing) reads additional bytes within the 128-byte window.
What is the difference between a header analyzer and a magic byte detector?
A magic byte detector identifies the file type by matching the first bytes against a signature database - it tells you what the file IS. A header analyzer goes further by parsing and explaining each field within the header - it tells you what each byte MEANS, including version numbers, dimensions, compression settings, color information, and other metadata encoded in the header structure.
Can the tool detect corrupted headers?
The tool checks if the file's header bytes match known format signatures. If the signature bytes are missing or incorrect (indicating a corrupted or truncated header), the tool will not report a match and will display the raw hex dump instead. You can compare the hex dump against the format specification to identify which bytes are corrupted.
Does the file get uploaded to a server?
No. The File Header Analyzer processes everything locally in your browser using the File API and Uint8Array operations. Only the first 128 bytes are read from the file, and those bytes are never sent to any server. Your files remain on your device throughout the entire process - no uploads, no data logging, no third-party requests.
What do the field importance levels mean?
Fields are marked with three importance levels: Critical (red indicator) - the field is essential for file identification, such as magic bytes or format signatures; Important (orange indicator) - key metadata like dimensions, version, or compression method; Normal (gray indicator) - supporting fields such as reserved bytes, padding, or optional descriptors. The field breakdown shows all fields regardless of importance.
What is a polyglot file and can this tool detect it?
A polyglot file is valid in two or more file formats simultaneously. For example, a file can be both a valid ZIP archive and a valid PNG image. The header analyzer detects the format that matches the file's header bytes - if a file starts with PNG magic bytes but also contains ZIP data, it will be identified as a PNG. Advanced polyglot analysis may require checking the full file structure.
Is this File Header Analyzer 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.