What is a byte-order mark?

The BOM is the Unicode codepoint U+FEFF placed at the start of a file. In UTF-16 it signals endianness, but in UTF-8 there is no byte order, so it acts purely as a signature that the file is UTF-8. It is encoded as the three bytes EF BB BF.

Why would I add a BOM?

Some applications, notably older versions of Microsoft Excel, only recognise a CSV file as UTF-8 if it begins with a BOM. Without it, accented characters and other non-ASCII text are misread. Adding the BOM fixes the import.

Why would I remove a BOM?

Many tools treat the BOM as unexpected data. A leading BOM can break shell scripts, PHP output, JSON parsers, and concatenated files by inserting invisible characters at the start. Stripping it cleans the file up.

How can I tell if my text already has a BOM?

A BOM is invisible on screen but adds three bytes (EF BB BF) at the very start. This tool reports the UTF-8 byte length before and after, and tells you whether the input already begins with U+FEFF.

Does adding a BOM twice stack them?

No. The tool checks for an existing BOM first and will not add a second one, and removal strips only a single leading BOM, so the operation is safe to apply repeatedly.

BOM Add / Remove Tool

The byte-order mark is a tiny, invisible character that causes outsized trouble. Some programs demand it, others choke on it. This tool lets you add or remove it precisely and confirms the change by byte count.

How it works

The BOM is the single Unicode codepoint U+FEFF. In UTF-8 it is serialised as three bytes:

EF BB BF

Adding a BOM prepends U+FEFF to the text if it is not already there. Removing a BOM strips one leading U+FEFF if present. To make the otherwise-invisible change verifiable, the tool encodes both the input and output to UTF-8 and reports the byte lengths — a difference of exactly three bytes is the BOM.

Tips and notes

For Excel CSV import of UTF-8 data, add the BOM so accented characters render correctly.
For shell scripts, JSON, PHP, and concatenated files, remove the BOM — a leading U+FEFF is a frequent cause of mysterious parse errors.
The output is plain text; paste it into your editor and save as UTF-8, or copy it into the destination application directly.