Bulk File Type Detector
Upload multiple files to detect their true file types by reading magic bytes (file signatures). Our Bulk File Type Detector reads the first 64 bytes of each file and matches them against a database of 65+ known signatures to identify the actual file format - regardless of the file extension. Extension mismatches are automatically highlighted for security audits, forensic analysis, and file integrity verification. All processing is done entirely in your browser - no uploads, no signup required.
Upload multiple files to detect their true file types by reading magic bytes (file signatures). The tool compares the detected type against the declared file extension and highlights mismatches - useful for security audits, file integrity verification, and forensic analysis. Supports 60+ file formats including images, documents, archives, audio, video, fonts, executables, and more. All processing is done entirely in your browser - no uploads, no signup required.
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Supports all file types - analyzed by magic bytes, not extensions
Every file format has a unique signature at the beginning of the file, called magic bytes or file signatures. These bytes are written by the application that created the file and remain unchanged even if the file extension is renamed. Our tool reads the first 64 bytes of each file and matches them against a database of 65+ known file signatures. This allows us to detect the true file type regardless of the declared extension - for example, a file renamed from document.pdf to document.jpg will still be correctly identified as a PDF.
Why Use Our Bulk File Type Detector?
Magic Byte File Signature Detection
Reads and matches the first 64 bytes of each file against a database of 65+ known file signatures. Detects the true file type regardless of the file extension or file name - a renamed .exe disguised as .pdf will be correctly identified. Supports images, documents, archives, audio, video, fonts, executables, certificates, and more.
Batch Processing for Multiple Files
Upload and analyze multiple files simultaneously. Each file is processed independently with its own result showing the detected type, matching status, and confidence level. Files are analyzed in parallel for fast results - perfect for auditing directories of files during security investigations or quality assurance checks.
Mismatch Detection & Alerts
Automatically compares the declared file extension against the detected file type. Mismatched files are clearly highlighted with warning indicators and color-coded alerts. Filter results by match status to quickly identify suspicious files - essential for security audits, malware detection, and file integrity verification.
100% Private Browser-Based Processing
All file analysis happens entirely in your browser. Files are read using the FileReader API and processed in-memory - no data is ever uploaded to any server. Your files never leave your device. This makes it safe to analyze sensitive or confidential files without privacy concerns.
Common Use Cases for Bulk File Type Detector
Security Incident Response & Forensics
During incident response, quickly scan directories of suspicious files to identify mislabeled executables, scripts disguised as documents, or files with mismatched extensions - common techniques used by malware authors to evade detection. The bulk analysis provides a fast overview of potentially dangerous files in your environment.
Malware Analysis & Threat Hunting
Analyze suspicious file collections for signs of tampering or masquerading. Threat hunters can quickly identify files where the extension has been changed to hide the true nature of the file - for example, a renamed .exe or .scr file pretending to be a .pdf or .jpg document.
Server File Integrity Auditing
Audit web server directories and file upload directories to ensure files match their expected types. Detect unauthorized file uploads where attackers may have uploaded executable files with innocent-looking extensions. Verify that uploaded media files are actually the type they claim to be.
File Upload Security Testing
QA and security teams can test file upload forms by submitting files with mismatched extensions to verify that the server properly validates file types by content, not just by extension. Helps identify common file upload bypass vulnerabilities.
Digital Forensics & Evidence Analysis
Digital forensics investigators can batch-analyze evidence files to verify their integrity and identify any files whose extensions have been altered. The hex header display provides additional forensic data for documentation and chain-of-custody reporting.
File Format Education & Research
Learn about file signatures and how different file formats are identified at the binary level. See the actual magic bytes of various file formats and understand how hex signatures correspond to human-readable format names. Great for cybersecurity students and computer science education.
Understanding File Types and Magic Bytes
What Are Magic Bytes?
Magic bytes (also called file signatures or magic numbers) are the first few bytes at the beginning of a file that uniquely identify its format. These bytes are written by the application that creates the file and remain constant for that file format. For example, every JPEG image starts with the bytes FF D8 FF, every PDF starts with 25 50 44 46('%PDF'), and PNG files start with an 8-byte signature 89 50 4E 47 0D 0A 1A 0A. Magic bytes are recognized by operating systems, file command utilities, and forensic tools to determine file types independently of file extensions.
How Our File Type Detector Works
- File Reading:When files are uploaded, our tool reads the first 64 bytes of each file into memory using the browser's FileReader API. Only the header bytes are read - not the entire file content. This makes the detection process extremely fast even for large files (e.g., a 4K video or a multi-gigabyte disk image).
- Signature Matching: The header bytes are compared against a comprehensive database of 65+ known file signatures. Each signature is checked at its known offset (usually at byte 0, but some formats like TAR have the signature at offset 0x101). If the bytes match, the file type is identified with exact confidence.
- Extension Comparison:The detected file type is compared against the file's declared extension. If they match, the file is marked as a match. If they don't match, the file is flagged as a mismatch with a warning indicator - this could indicate a mislabeled file or a deliberate attempt to hide the file's true nature.
- Hex Display: The first 24 hex bytes of each file are displayed, allowing you to manually verify the magic bytes. This is useful for forensic documentation and for learning to recognize file signatures visually.
Why File Extension vs Magic Byte Checking Matters
- Security: Attackers often rename malicious files to have innocent-looking extensions (e.g.,
evil.exerenamed todocument.pdf). Magic byte detection bypasses this trick by checking the actual file content. - Data Recovery: When files are recovered from damaged storage, their extensions may be lost or corrupted. Magic byte analysis can identify the original file format so it can be properly restored.
- Quality Assurance: File upload systems should validate file types by content, not just by extension. Bulk file type detection helps QA teams verify that upload validation is working correctly.
- Forensics: In digital investigations, file extension mismatches can be evidence of tampering. Documenting the true file type via magic bytes is a standard forensic practice.
Privacy, Security & Limitations
Our Bulk File Type Detector processes everything entirely in your browser. Files are read using the FileReader API and analyzed in-memory - no data is ever uploaded to any server. The tool is 100% free with no signup, no account, and no usage limits.
Supported formats: 65+ file types across images (JPEG, PNG, GIF, WebP, BMP, TIFF, AVIF, ICO, HEIC, SVG, PSD), documents (PDF, DOC, DOCX, XLSX, PPT, ODT, RTF, EPUB), archives (ZIP, RAR, 7z, GZIP, BZIP2, XZ, Zstandard, TAR, DMG, ISO), audio (MP3, FLAC, WAV, AIFF, OGG, M4A, WMA, AMR, MIDI), video (AVI, MPEG, MKV, WebM, FLV, MOV, WMV), fonts (TTF, OTF, WOFF, WOFF2, EOT), and executables (ELF, PE, Mach-O, SWF, WASM).
Limitations:Files with unrecognized or custom formats will show as "Unknown." Files smaller than the required signature offset may not be detectable. Some formats (like ZIP-based formats) may match multiple signatures - the first matching signature is returned. Encrypted or obfuscated files may not have recognizable signatures. The tool cannot detect file types from file content alone if the signature database doesn't include that format.
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Frequently Asked Questions About Bulk File Type Detector
Magic bytes are fixed byte sequences at the beginning of files that uniquely identify their format. They are written by the application that creates the file and remain constant - not even renaming a file changes its magic bytes. This makes them the most reliable method for determining a file's true type, as file extensions can be easily changed. Operating systems and forensic tools have used magic byte detection for decades.
Our Bulk File Type Detector supports 65+ file formats across all major categories: images (JPEG, PNG, GIF, WebP, BMP, TIFF, AVIF, ICO, HEIC, SVG, PSD), documents (PDF, DOC, DOCX, XLSX, PPT, ODT, RTF, EPUB, MOBI), archives (ZIP, RAR, 7z, GZIP, BZIP2, XZ, Zstandard, TAR, DMG, ISO), audio (MP3, FLAC, WAV, AIFF, OGG, M4A, WMA, AMR, MIDI), video (AVI, MPEG, MKV, WebM, FLV, MOV, WMV), fonts (TTF, OTF, WOFF, WOFF2, EOT), executables (ELF, PE/EXE, Mach-O, SWF, WASM), and more (SQLite databases, certificates, Chrome extensions).
A mismatch occurs when the declared file extension (e.g., .pdf) does not match the detected file type (e.g., PE/EXE). This could mean: the file was renamed (possibly to hide its true nature), the file was incorrectly saved with the wrong extension, or the extension was accidentally changed. Mismatches are highlighted in red with a warning icon for easy identification.
A file shows as "Unknown" when its magic bytes do not match any signature in our database. This can happen for: custom or proprietary file formats, very new file formats not yet added to our database, files with damaged or missing headers, or files that are empty or too small to read a signature. The tool shows the hex bytes of the header even for unknown files, which may help in manual identification.
You can upload and analyze as many files as your browser can handle. Each file is processed independently in parallel using Promise.all, so performance depends on your browser's capabilities. For practical purposes, uploading a few dozen files at once works perfectly. The tool displays a summary with match/mismatch counts and a filterable results list for easy navigation.
Yes. All file analysis happens entirely in your browser using the FileReader API. Only the first 64 bytes of each file are read, and no data is ever uploaded to any server. Your files never leave your device. You can verify this by checking your browser's Network tab - there will be no network requests during the analysis process.
Yes! This is a primary use case. Security testers can create test files with mismatched extensions and verify that the target server correctly validates file types by content. For example, rename a .exe to .pdf and test if the server accepts the upload. Then use our tool to confirm the file was correctly identified by content.
Yes! 100% free with no signup, no account, no API key, and no usage limits. Analyze as many files as you need - completely free, forever. All processing happens in your browser with no server costs, so there are no limits on usage.