Invisible text

Type a message and it's hidden inside the words in Hide it in. The output looks exactly like the cover text, and copying it copies the hidden message too. Anyone with this page can read it back, so don't hide anything in it that matters.

To check a piece of text, press swap and paste it in. Anything hidden with either method is shown. If there's no message but the text still carries invisible characters, the tool says which ones and how many.

Method picks how the message is hidden. Tag characters are one invisible character per letter, but only for plain English letters, digits and punctuation. Zero-width binary writes each bit as one of two invisible characters, so it carries accents and emoji too, at eight characters a byte.

Language models read characters that people can't see. A web page, an email or a document can carry instructions written in tag characters, and a model asked to summarise it may follow them. The technique is called ASCII smuggling. In 2024 the researcher Johann Rehberger showed it could steer Microsoft 365 Copilot into hiding data from a user's mailbox, including sign-in codes, inside an innocent-looking link. Microsoft fixed it after he reported it.

Paste anything suspicious here and swap before handing it to an AI tool. The text cleaner strips the zero-width characters from a paste as well, and this page tells you whether there was a message in them.

The tag characters, U+E0020 to U+E007E, are a copy of printable ASCII that draws nothing. They were added for tagging text with its language invisibly, following RFC 2482 in January 1999, and were deprecated in Unicode 5.1 when better ways to mark language won out.

Unicode 8.0 lifted the deprecation in 2015, and in 2017 Emoji 5.0 put them to work. A flag like Scotland's is a black flag followed by tag characters spelling the region's code, so every one of those flags already carries a short invisible message. This tool uses the same characters to carry yours.