BOM Detector
Upload any file to detect Byte Order Marks (BOMs) and identify the text encoding. Our BOM Detector reads the file header and matches it against known BOM signatures for UTF-8, UTF-16 (Big Endian and Little Endian), UTF-32, UTF-7, GB 18030, and more. View the interactive hex dump with BOM bytes highlighted, get detailed encoding information with endianness detection, and receive practical recommendations for cross-platform compatibility. All processing is done entirely in your browser - no uploads, no signup required.
Upload any file to detect Byte Order Marks (BOMs) - hidden byte sequences at the start of files that identify the text encoding and byte order. Supports UTF-8, UTF-16 (BE/LE), UTF-32 (BE/LE), UTF-7, GB 18030, and other BOM signatures. Displays the hex dump with BOM bytes highlighted, encoding details, and recommendations for cross-platform compatibility. All processing is done entirely in your browser - no uploads, no signup required.
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Detects BOM signatures in text and binary files
Why Use Our BOM Detector?
Comprehensive BOM Signature Detection
Detects all standard Byte Order Mark signatures: UTF-8 (EF BB BF), UTF-16 Big Endian (FE FF), UTF-16 Little Endian (FF FE), UTF-32 Big Endian (00 00 FE FF), UTF-32 Little Endian (FF FE 00 00), UTF-7 (+/v), UTF-1, SCSU, BOCU-1, and GB 18030. Each BOM is identified with its encoding name, IANA charset, endianness, and common usage context.
Interactive Hex & ASCII Display
Displays the first 48 bytes of the file as an interactive hex dump with side-by-side ASCII representation. Detected BOM bytes are highlighted in amber for easy visual identification. The hex data can be copied to clipboard with one click for documentation or further analysis.
Encoding Recommendations
Provides actionable recommendations based on the detected BOM encoding. Advises on cross-platform compatibility issues - for example, warning when UTF-8 BOM is detected in source code that may cause issues on Unix/Linux systems, or suggesting conversion from UTF-16 to UTF-8 for better storage efficiency and tool compatibility.
100% Private Browser-Based Processing
All BOM detection happens entirely in your browser. Only the first 1024 bytes of the file are read using the FileReader API - no data is ever uploaded to any server. Your files never leave your device, making it safe to analyze sensitive or proprietary files.
Common Use Cases for BOM Detector
Debugging Encoding Issues in Web Development
When PHP, Python, or JavaScript files show unexpected output (like  characters at the top of a web page), the UTF-8 BOM is often the culprit. Use our BOM Detector to quickly identify whether source files have a BOM, then convert to UTF-8 without BOM for clean rendering.
Cross-Platform File Compatibility
Files created on Windows often include a UTF-8 BOM that causes issues when transferred to Unix/Linux/macOS systems. Scripts with shebang lines (#!) may fail, configuration files may be misread, and diff tools may show phantom differences. Detect BOMs to diagnose and resolve these compatibility issues.
CSV & Data File Encoding Verification
CSV files exported from Microsoft Excel often include a UTF-8 BOM, which can affect how data processing tools parse the file. Detect the BOM and encoding to ensure your ETL pipelines, database imports, and data analysis tools handle the file correctly.
Legacy File Format Migration
When migrating legacy systems that use UTF-16, UTF-32, or GB 18030 encoding to modern UTF-8 standards, use BOM detection to identify which files need conversion. The recommendation engine provides guidance on the best conversion strategy for each encoding type.
QA & File Validation in CI/CD Pipelines
Integrate BOM detection into your quality assurance workflow. Ensure all source code, configuration files, and documentation follow your team's encoding standards. Detect and flag files with unexpected BOMs before they cause production issues.
Computer Science & Unicode Education
Learn about Unicode encoding, byte order, endianness, and the BOM character (U+FEFF) interactively. Upload files in different encodings and observe how the BOM signatures differ. A practical teaching tool for courses on internationalization and character encoding.
Understanding Byte Order Marks (BOM)
What is a Byte Order Mark (BOM)?
A Byte Order Mark (BOM) is a Unicode character (U+FEFF) that is placed at the beginning of a text file to indicate its encoding and byte order. The BOM was designed to solve a fundamental problem with multi-byte encodings: different computer architectures store multi-byte values in different byte orders (endianness). By reading the first few bytes of a file, a program can determine whether the text is encoded in UTF-8, UTF-16 Big Endian, UTF-16 Little Endian, or another format, and interpret the subsequent bytes correctly. The BOM is specified in the Unicode standard and is recognized by many text editors, web browsers, and programming language runtimes.
How Our BOM Detector Works
- File Reading:When you upload a file, our tool reads the first 1024 bytes using the browser's FileReader API. Only the header is read, making the detection process fast even for large files.
- BOM Signature Matching: The bytes at the start of the file are compared against a database of 10 known BOM signatures. Each signature is checked byte-by-byte for an exact match. If a BOM is found, the encoding, endianness, and IANA charset are identified.
- Deep Scan: In addition to checking the start of the file, the tool scans deeper (up to 128 bytes) for additional BOM-like patterns. This helps detect concatenated files or unusual file structures that may have BOMs at non-zero offsets.
- Recommendation Generation: Based on the detected encoding, the tool provides tailored recommendations for cross-platform compatibility, storage efficiency, and tool interoperability.
When to Use (and Not Use) BOMs
- UTF-8 with BOM (EF BB BF):Common on Windows but can cause issues on Unix/Linux. PHP scripts with BOM will cause "headers already sent" errors. Python scripts may fail on the shebang line. Shell scripts may silently break. Recommended: Use UTF-8 without BOM for web content and source code.
- UTF-16 BOMs (FE FF / FF FE): Essential for identifying byte order in UTF-16 files. Required by some Windows APIs and .NET applications. However, UTF-16 files are harder to process with standard Unix tools (grep, sed, awk) and take up more space for ASCII-heavy content.
- UTF-32 BOMs (00 00 FE FF / FF FE 00 00): Very rarely used. UTF-32 quadruples the storage size compared to UTF-8 for most text and is supported by very few applications. Not recommended for general use.
- Non-Unicode BOMs: GB 18030 BOM is used in Chinese government systems. Other encoding markers (UTF-7, SCSU, BOCU-1, UTF-1) are obsolete or extremely rare in modern applications.
Privacy, Security & Limitations
Our BOM Detector processes everything entirely in your browser. Only the first 1024 bytes of each file are read - no data is ever uploaded to any server. The tool is 100% free with no signup, no account, and no usage limits.
Supported BOM signatures: UTF-8, UTF-16 BE/LE, UTF-32 BE/LE, UTF-7, UTF-1, SCSU, BOCU-1, and GB 18030 - covering all standard BOM signatures defined in the Unicode standard and related encoding specifications.
Limitations:BOM detection only identifies the encoding marker - it does not validate whether the rest of the file conforms to that encoding. Files without BOMs (like most UTF-8 files on Unix/Linux) will show as "No BOM Found." Binary files may coincidentally start with bytes that match BOM signatures, potentially producing false positives. The tool reads only the first 1024 bytes; BOMs beyond this range will not be detected.
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Frequently Asked Questions About BOM Detector
A Byte Order Mark (BOM) is a Unicode character (U+FEFF) encoded at the beginning of a text file that identifies the encoding and byte order used. The BOM appears as different byte sequences depending on the encoding: EF BB BF for UTF-8, FE FF for UTF-16 Big Endian, FF FE for UTF-16 Little Endian, and so on. It helps software correctly interpret the text encoding without guessing.
Our BOM Detector supports 10 BOM signatures: UTF-8 with BOM (EF BB BF), UTF-16 Big Endian (FE FF), UTF-16 Little Endian (FF FE), UTF-32 Big Endian (00 00 FE FF), UTF-32 Little Endian (FF FE 00 00), UTF-7 (2B 2F 76), UTF-1 (F7 64 4C), SCSU (0E FE FF), BOCU-1 (FB EE 28), and GB 18030 (84 31 95 33).
For most modern web development and cross-platform scenarios, UTF-8 without BOM is recommended. The BOM is unnecessary for UTF-8 (since UTF-8 has no byte order issues) and can cause problems with PHP scripts ("headers already sent"), Python interpreters, shell scripts with shebang lines, and Unix command-line tools. Windows applications (like Notepad) default to UTF-8 with BOM.
Yes, binary files can coincidentally start with byte sequences that match BOM signatures. For example, a compiled executable might start with 0xFF 0xFE (matching UTF-16 LE BOM) or 0xEF 0xBB 0xBF (matching UTF-8 BOM). The tool performs exact byte matching and will report any match found. Consider the file type context when interpreting results.
The  characters are the visible representation of the UTF-8 BOM (EF BB BF) when interpreted as Latin-1 or Windows-1252 encoding. This typically happens when a PHP file was saved with UTF-8 BOM encoding in a Windows editor. The BOM causes the "headers already sent" error in PHP because it outputs data before the script's <?php tag.
Our tool reads the first 1024 bytes (1 KB) of the file. This is more than sufficient for BOM detection since BOMs are at most 4 bytes long. The remaining bytes of the header are displayed as a hex dump for manual inspection.
Yes. All file analysis happens entirely in your browser using the FileReader API. Only the first 1024 bytes are read, and no data is ever uploaded to any server. Your files never leave your device.
Yes! 100% free with no signup, no account, no API key, and no usage limits.