How does zero-width steganography work?

Each character of the secret is converted to 8 bits. A bit value of 0 is stored as a zero-width space (U+200B) and a bit value of 1 as a zero-width joiner (U+200D). These characters take no visible space, so the cover text looks unchanged.

Why is the hidden text invisible?

Zero-width characters are real Unicode code points designed for typographic control, but they render with no width. Embedded among normal letters they are imperceptible to a reader while still surviving copy and paste.

No. It is concealment, not encryption. Anyone who knows the zero-width scheme can decode the payload, so encrypt the secret first if you need genuine confidentiality.

Where does the payload sit in the cover text?

This tool appends the zero-width sequence after the first character of the cover text so it is carried inside the string. Decoding scans the whole string for zero-width characters regardless of position.

Will the hidden message survive everywhere?

Often on platforms that preserve Unicode, such as chat apps, documents and many web forms. Some systems strip or normalise zero-width characters, which would erase the payload, so test your channel first.

What is the Zero-Width Character Steganography?

Embed a secret message into invisible zero-width Unicode characters, encoding each bit as a zero-width space or zero-width joiner. Decode any zero-width-tagged text back to the hidden message. It runs free in your browser on Gera Tools, with nothing uploaded.

Zero-Width Character Steganography

Name: Zero-Width Character Steganography
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

What this tool does

This is a zero-width steganography encoder and decoder. It hides a secret message inside invisible Unicode characters that occupy no visible space, so the cover text appears completely normal while secretly carrying your payload.

How it works

The encoder uses two zero-width code points as binary digits:

Zero-width space U+200B represents bit 0
Zero-width joiner U+200D represents bit 1

Each character of the secret is converted to its 8-bit value, every bit is mapped to one of those two invisible characters, and the sequence is embedded into the cover text. To keep the payload self-contained, the tool also frames it with a zero-width non-joiner U+200C boundary marker so the decoder knows exactly where the hidden data starts and ends.

Decoding scans the text for these zero-width characters, converts each back to a 0 or 1, regroups the bits into bytes, and reconstructs the original characters.

Step-by-step example

The letter H has ASCII code 72, which is 01001000 in binary. Encoded, it becomes eight invisible characters in sequence:

0 → U+200B (zero-width space)
1 → U+200D (zero-width joiner)
0 → U+200B
0 → U+200B
1 → U+200D
0 → U+200B
0 → U+200B
0 → U+200B

These eight characters are completely invisible in a text editor, browser, or chat message. The decoder simply reverses the process: extract U+200B/U+200D characters, map each to 0 or 1, group into 8-bit chunks, and recover the ASCII character.

A four-character secret like Hi! generates 32 zero-width characters inside the cover text — still completely invisible to any reader.

Payload size

Payload size grows linearly with the secret: each character of the secret requires 8 zero-width code points. A 10-character secret adds 80 invisible characters to the cover text. This is imperceptible visually but may be detectable by byte-length inspection — the encoded text will be significantly longer in bytes than it appears.

Where zero-width characters survive

Zero-width Unicode characters are preserved in:

Most rich text editors (Google Docs, Word, Notion)
Web forms and databases that store Unicode faithfully
Chat apps that transmit full Unicode (Telegram, WhatsApp, Signal)
Email body text

They are often stripped or normalised in:

Plain-text terminals (some strip U+200B)
Some social media platforms that sanitise Unicode
SMS (constrained encoding)
Any system that converts to ASCII or Latin-1

Always test your specific delivery channel before relying on the payload surviving.

This is not encryption

Zero-width steganography provides concealment (the message is hidden) but not confidentiality (it is not scrambled). Anyone who suspects zero-width encoding and extracts the invisible characters can read the message in plain text. To achieve genuine secrecy, encrypt the payload before encoding it — then the extracted bits reveal only ciphertext, not the message.

Notes

Encrypt first if you need secrecy; this tool provides concealment only.
Some platforms normalise or strip zero-width characters; verify your delivery channel preserves them.
Because the payload is pure Unicode, it survives ordinary copy-paste better than trailing whitespace steganography does.
To detect whether a piece of text contains zero-width characters, paste it into a hex editor or Unicode inspector and look for U+200B, U+200C, or U+200D.