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UTF-8 BOM Checker
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Detect and remove BOM signatures from UTF-8 files in one click. Fix parsing errors in PHP and optimize file compatibility.
Choose filesDrag files here or click to upload
Supports all text files (HTML, CSS, JS, TXT, etc.)
Max 5 MB
A BOM (Byte Order Mark) is a special marker at the start of a file (0xEF, 0xBB, 0xBF) used to indicate UTF-8 encoding.
While a BOM can help some Windows programs (such as Notepad), it is usually recommended to use no BOM in web development because:
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
A byte order mark (BOM) is a marker that can appear at the very start of a text stream. For UTF-8, the marker's three bytes are EF BB BF. The Unicode Consortium describes this sequence as a possible signature for UTF-8 text; UTF-8 itself does not require the marker. This checker reports whether a selected file begins with exactly those three bytes. It checks only the opening bytes, not the whole file's character encoding. See the Unicode FAQ on BOMs.
BOM present means the first three bytes matched EF BB BF. Some software accepts or removes that marker when reading text; other formats or programs expect a different opening sequence. No BOM means only that this particular UTF-8 signature was not found at byte zero. A file may still be valid UTF-8 without a BOM, or it may use another encoding. The result does not certify that the file is UTF-8, and this check does not identify UTF-16 or UTF-32 signatures.
After files are selected, the list shows the name, size, and BOM status for each item. The tool can also derive a short preview from the first 100 bytes using UTF-8 decoding. A preview is only a quick visual aid: it may show replacement characters when those bytes are not valid UTF-8, and it is not a full text inspection. The checker reads files up to 5 MB each and allows multiple files to be selected.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use the file area to choose text files from your device. Each individual file must be no larger than 5 MB.
The result appears next to each filename as either BOM present or no BOM. Check the matching file row if you are working with a batch.
Use the remove control beside a file to take it out of the displayed list. The checker reports status; it does not rewrite, clean, or download a modified file.
For a known UTF-8-with-BOM example, the first bytes are EF BB BF followed by the file's content. A plain UTF-8 file may begin directly with its first text byte and correctly report no BOM.
Use cases
See how the tool fits into real work and everyday tasks.
If an application reports an unexpected character at the beginning of a text file, check whether the UTF-8 signature is present before investigating the importer’s encoding expectations.
Compare files from different export settings to see whether one begins with EF BB BF. This can help document a workflow, but does not determine which file will be accepted by a particular system.
Try a UTF-8 file with and without the leading marker to understand what a signature check can detect and why a negative result is not an encoding diagnosis.
Q&A
Find concise answers to common questions and confusing cases.
No. UTF-8 files do not need a BOM, and files in other encodings can also lack these three bytes. Use an encoding-aware parser or inspect the file with a suitable text editor when the encoding matters.
No. It tests only the initial UTF-8 sequence EF BB BF. A different encoding marker will be reported as no UTF-8 BOM.
No. It displays whether the signature is present but does not alter or export the selected file. Use an editor or a file-processing workflow that explicitly supports BOM removal if you need to change it.
The preview decodes only the first 100 bytes as UTF-8. Non-UTF-8 data, a multibyte character cut off at the preview boundary, or other binary content may display unexpectedly.
Notes
Review scope, result limitations, and important precautions before use.
The result is a signature check, not a complete encoding validator or a guarantee that an application will accept the file. The selected file remains unchanged by this check. Confirm the format requirements of the program that will read the file before removing or adding a BOM, because some protocols expect particular characters at the beginning.
Related
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