Strip BOM

BOM stands for byte order mark, an optional marker at the start of a file that signals its encoding. In UTF-16 it does a real job, indicating byte order. In UTF-8 it is unnecessary, yet Notepad and various Microsoft tools add it anyway, writing the three bytes EF BB BF before the first real character.

The damage is always the same: an invisible character where nothing should be. In PHP, output before a header triggers "headers already sent". In CSV, the first header column gets junk in its name and the import cannot find the field. In JSON, the parser rejects the entire file. In a shell script, the shebang line stops being recognised. Paste the text here and the page reports whether a BOM was present and hands back the content without it.

Detection looks at the first character and checks for U+FEFF. Worth knowing: the browser sometimes strips the marker during paste, which makes the page report none even for content that had a BOM on disk — to check the file itself, use hexdump -C file | head -1 and look at the first three bytes. To save without the marker, virtually every editor offers a "UTF-8 without BOM" encoding option.