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Free Online Atbash Encoder and Decoder Encrypt and decrypt text using the Atbash reverse-alphabet cipher.

Atbash Cipher illustration
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Atbash Cipher

Encrypt and decrypt text using the Atbash reverse-alphabet cipher.

1

Enter text

Type or paste text into the input field. Letters A–Z and a–z are transformed; numbers and punctuation stay unchanged.

2

View output

The Atbash result appears in real time as you type.

3

Copy result

Click Copy to copy the transformed text to your clipboard.

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What Is Atbash Cipher?

Oldest known cipher from Hebrew alphabet (~500 BCE). Replaces each letter with its reverse: A-Z, B-Y, C-X. Name from Hebrew Aleph-Tav, Beth-Shin. Self-inverse (involution). Appears in the Book of Jeremiah. Pure JavaScript.

Why Use Atbash Cipher?

  • Fast, accurate processing
  • 100% client-side — data never leaves your browser
  • Free online tool with no signup required
  • Mobile-friendly with 44px touch targets

Common Use Cases

Learning substitution ciphers

Students and cryptography beginners practice encoding and decoding with a classic reverse-alphabet cipher.

Puzzles and games

Decode clues in escape rooms, treasure hunts, or puzzle games that use Atbash.

Hebrew text and history

Study how the cipher was used in ancient Hebrew texts such as the Book of Jeremiah.

Quick obfuscation

Hide plain text from casual glance when full encryption is not needed.

Technical Guide

E(x) = 25-x. E(E(x)) = x (involution). Uppercase: 155-charCode. Lowercase: 219-charCode. Non-alphabetic unchanged. Equivalent to affine cipher a=25, b=25. One key — zero security.

Tips & Best Practices

  • 1
    Letters A–Z and a–z are reversed; numbers, spaces, and punctuation stay unchanged.
  • 2
    Encoding and decoding use the same operation—apply Atbash twice to get the original.
  • 3
    Use the Copy button to grab the output without selecting manually.
  • 4
    Try "hello" → "svool" to verify the cipher works as expected.

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Frequently Asked Questions

Q How does the Atbash cipher work?
It replaces each letter with its opposite in the alphabet: A↔Z, B↔Y, C↔X, and so on.
Q What is the purpose of Atbash?
It creates a simple encoding scheme using a fixed substitution. Easy to implement and understand, but offers no real security.
Q Can Atbash handle numbers?
No. It only transforms letters. Numbers, punctuation, and spaces pass through unchanged.
Q Is Atbash case-sensitive?
Yes. Uppercase stays uppercase and lowercase stays lowercase in the output.
Q How do I decode Atbash-encoded text?
Apply the same cipher again. Atbash is self-inverse, so encoding and decoding use the same operation.

About This Tool

Atbash Cipher is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.