Encode and decode Atbash - the keyless A-Z reversal cipher (A becomes Z, B becomes Y). Self-inverse, instant, with a live alphabet map. Free, in-browser.
This Atbash tool encodes and decodes text with the classic reverse-alphabet substitution — A becomes Z, B becomes Y, C becomes X, and so on to the end of the alphabet. Type in either box and the result updates instantly, with a live alphabet map showing every letter paired to its mirror. What makes Atbash unusual, and worth its own tool, is that it has no key: the mapping is fixed, and because it is a mirror it is its own inverse. Running Atbash twice returns the original text, so there is a single button for both directions. Everything runs in your browser — nothing is uploaded.
Atbash sits at the very bottom of the cryptography ladder, and that is exactly why it is useful to understand. It is a fixed monoalphabetic substitution: one letter always maps to the same other letter, with no shift value and no keyword to remember. That fixedness is its entire character, and it is what distinguishes Atbash from every other classical cipher on this site.
InventiveHQ hosts a full shelf of classical ciphers, and it is worth being precise about where Atbash fits, because it is easy to lump them together:
If you are trying to identify an unknown cipher rather than apply a known one, the cipher identifier can help narrow it down; Atbash's tell is that E (the most common English letter) consistently appears as V.
Number the alphabet A=0 through Z=25. Atbash maps each position x to 25 - x. So A (0) goes to Z (25), B (1) to Y (24), M (12) to N (13), and N (13) back to M (12). There is no modular arithmetic and no key term — it is a straight reflection about the middle of the alphabet. A worked example:
| Plaintext | Position | 25 − position | Ciphertext |
|---|---|---|---|
| H | 7 | 18 | S |
| E | 4 | 21 | V |
| L | 11 | 14 | O |
| L | 11 | 14 | O |
| O | 14 | 11 | L |
So HELLO becomes SVOOL, and applying Atbash to SVOOL returns HELLO. The self-inverse property falls straight out of the arithmetic: applying 25 - x twice gives 25 - (25 - x) = x.
Atbash provides no real security, and it is important to be honest about why. There is only one possible mapping, so there is no key space to search — recognising that a message is Atbash is breaking it. Even if you did not know the cipher, it is a fixed monoalphabetic substitution, which means standard frequency analysis cracks it immediately: the most common ciphertext letter will be V (the mirror of E), and short common words have fixed shapes (THE always enciphers to GSV). Treat Atbash as a puzzle, a teaching example, or a light obfuscation for CTF challenges and geocaching clues — never as protection for anything that matters. For genuine confidentiality you need modern authenticated encryption, not a classical cipher.
Atbash is one of the oldest recorded ciphers, appearing in the Hebrew Bible where it was used on Hebrew letters (the name itself comes from Aleph-Tav-Beth-Shin, the first, last, second and second-to-last Hebrew letters). Today you will meet it in beginner cryptography courses as the simplest possible substitution, in Capture The Flag warm-up rounds, in escape rooms and puzzle hunts, and occasionally as a layer inside a multi-stage puzzle where spotting the reversed alphabet is the “aha” step.
No. The mapping is fixed — every A becomes Z, every B becomes Y, and so on. There is nothing to configure or remember, which is the main thing that sets it apart from Caesar, Vigenère and substitution ciphers.
Atbash is self-inverse. Because it reflects the alphabet onto itself, applying it a second time undoes the first, so a single operation handles both directions.
SVOOL. Applying Atbash to SVOOL gives HELLO back.
No. It offers no meaningful security. With only one possible mapping, identifying the cipher is equivalent to breaking it, and frequency analysis cracks it instantly. Use it only for puzzles and learning.
Both are keyless self-inverse substitutions, but ROT13 shifts each letter 13 places (A to N), while Atbash reverses the alphabet (A to Z). ROT13 is a fixed Caesar shift; Atbash is a mirror.
Yes. Only letters are transformed. A toggle lets you preserve spaces, digits and punctuation as-is or strip non-alphabetic characters, and another toggle preserves upper and lower case.
The most frequent letter tends to be V (the mirror of E), and common words keep fixed shapes — THE always becomes GSV. The cipher identifier automates this kind of detection.
Because Atbash needs no key, solving it by hand is quick once you recognise it, and recognising it is the whole trick. If a piece of ciphertext looks like a monoalphabetic substitution — word lengths and spacing intact, but the letters scrambled — try Atbash first, because it is the simplest fixed mapping. The fastest tell is to look at single-letter words and very common short words: in Atbash, A becomes Z, I becomes R, and THE becomes GSV. If you spot GSV repeated where you would expect “the”, you are almost certainly looking at Atbash and can decode the rest by reflecting each letter. This tool does the reflection for you, but knowing the reasoning is what lets you identify the cipher in the first place, which is often the actual challenge in a CTF or puzzle hunt.
Atbash is also frequently used as one layer in a stacked puzzle — for instance, text that has been Atbash-encoded and then Base64-encoded, or Atbash applied after a Caesar shift. When a single pass of Atbash produces something that is still gibberish but has a different character distribution, that is a hint another layer is involved. Chaining this tool with the others in the cipher shelf lets you peel those layers one at a time.
Compare Atbash with the keyed Caesar cipher, the fixed-shift ROT13, and the full-alphabet substitution cipher, or run unknown text through the cipher identifier to work out which classical scheme you are looking at.
Not sure which cipher you have? Use the Cipher Identifier to auto-detect cipher types from unknown ciphertext using frequency analysis and Index of Coincidence.
Atbash is a monoalphabetic substitution cipher that maps each letter of the alphabet to its mirror image: the first letter to the last, the second to the second-to-last, and so on. In English, A becomes Z, B becomes Y, C becomes X, all the way through M↔N. Because the mapping is a self-inverse, applying Atbash twice returns the original plaintext — the same operation encodes and decodes.
Number the alphabet 0–25 (A=0, B=1, ..., Z=25). The Atbash substitution is simply:
ciphertext letter = 25 − plaintext letter (mod 26)
The full English substitution table is:
| Plain | A | B | C | D | E | F | G | H | I | J | K | L | M | | Cipher | Z | Y | X | W | V | U | T | S | R | Q | P | O | N |
So "HELLO" encodes as "SVOOL": H(7)→S(18), E(4)→V(21), L(11)→O(14), L→O, O(14)→L(11). Running "SVOOL" through Atbash again returns "HELLO" because each pair is its own inverse.
Atbash was originally designed for the Hebrew alphabet, where aleph (the first letter) maps to tav (the last), bet maps to shin, and so on — the cipher's name "atbash" comes from concatenating those four letters: aleph-tav-bet-shin.
Atbash dates to roughly 500 BCE and appears in the Hebrew Bible. The Book of Jeremiah uses Atbash to encode the place name "Babel" (בבל) as "Sheshach" (ששך) — likely as a literary device rather than serious secrecy. It is one of the earliest documented substitution ciphers and predates the Caesar cipher by several centuries.
Never for real security — Atbash has a fixed key, so once anyone knows it is Atbash, the message is fully recovered with no further work. It is useful for:
Atbash is trivially broken. Because the mapping is fixed and public, anyone who suspects Atbash can decode the message in seconds. Even without knowing it is Atbash, the cipher leaves a strong fingerprint: it is a monoalphabetic substitution, so the letter frequency distribution of the ciphertext is just the English distribution mirrored. The Index of Coincidence is ~0.067, identical to English plaintext.
Standard cryptanalysis steps:
If you have ciphertext and aren't sure whether it is Atbash, ROT13, or a different substitution, start with the Cipher Identifier.