Is the Caesar cipher secure encryption?

No. The Caesar cipher, ROT13, ROT47, and Atbash have no secret key and can be reversed by anyone in seconds — a Caesar shift can even be cracked by trying all 25 keys, which this tool does for you. Use them for puzzles, obfuscation, or hiding spoilers, never to protect sensitive data. For real security use a modern algorithm such as AES.

What is ROT13, and how is it different from ROT47?

ROT13 is a Caesar cipher with a fixed shift of 13 that affects the 26 letters only. ROT47 rotates all 94 printable ASCII characters (codes 33 to 126) by 47, so letters, digits, and punctuation all change. Both are their own inverse, meaning the same operation encodes and decodes.

How do I decode a Caesar cipher if I do not know the shift?

Enable the brute-force table. It lists your text decrypted with all 25 possible shifts at once; read down the rows until one reads as normal language. The shift labelled on that row is the key that was used, and you can copy that line directly.

Does the tool keep capitalization and punctuation?

Yes. In Caesar, ROT13, and Atbash modes, uppercase stays uppercase, lowercase stays lowercase, and spaces, punctuation, and other symbols pass through unchanged. Digits are only altered if you enable the "Also shift digits" option. ROT47 intentionally transforms digits and symbols as well as letters.

Atbash is an ancient substitution cipher that mirrors the alphabet: A maps to Z, B to Y, C to X, and so on. It affects letters only and, like ROT13, is its own inverse, so encoding and decoding are the same operation.

Is my text uploaded to a server?

No. All encoding, decoding, and brute-forcing happen entirely in your browser with JavaScript, so your text never leaves your device.

Caesar Cipher & ROT13 Encoder / Decoder

Caesar Cipher, ROT13, ROT47 & Atbash Encoder / Decoder

This free tool encodes and decodes classic shift and substitution ciphers: the Caesar cipher (any shift from 0 to 25), ROT13, ROT47, and Atbash. Pick a mode, choose a shift and direction, and the transformed text appears instantly. Letter case is preserved and anything that is not a letter — spaces, punctuation, and symbols — passes through unchanged (except in ROT47, which by design also rotates digits and symbols).

It is built for puzzles, CTFs, escape rooms, classroom demos, hiding spoilers, and lightweight obfuscation. These are historical ciphers with no secret key, so they offer no real security — anyone can reverse them, and this tool includes a brute-force table that cracks a Caesar shift in seconds. Everything runs locally in your browser; the text you paste is never uploaded.

How to use Caesar Cipher (ROT13)

Choose a cipher mode: Caesar shift, ROT13, ROT47, or Atbash.
For Caesar mode, set the Shift amount (0 to 25) with the slider and choose Encode (shift forward) or Decode (shift back). ROT13, ROT47, and Atbash are their own inverse, so the same operation both encodes and decodes.
Type or paste your text into the Input box — the Output updates live as you type.
Optionally enable "Also shift digits 0-9" to rotate numbers as well (with ROT13 this applies ROT5, together known as ROT18).
To crack a message whose shift you do not know, tick "Show brute-force table" and read down the 25 rows for the one that makes sense — its shift number is the key.
Copy the output, download it as a .txt file, or use "Use as input" to feed it back in and verify a round-trip.

Cipher modes explained

Caesar shift — replaces each letter with the one a fixed number of places later in the alphabet, wrapping around from Z to A. A shift of 3 (A becomes D) is the cipher attributed to Julius Caesar. Decoding simply shifts back by the same amount.
ROT13 — a Caesar cipher with a fixed shift of 13. Because 13 is half of 26, applying it twice returns the original text, so one operation both encodes and decodes. It is widely used to hide spoilers and puzzle answers in plain sight.
ROT47 — rotates every printable ASCII character (codes 33 to 126) by 47 places, so letters, digits, and punctuation all change. Like ROT13 it is its own inverse; spaces and line breaks are left untouched.
Atbash — mirrors the alphabet, mapping A to Z, B to Y, C to X, and so on. It is an ancient Hebrew substitution cipher and is also its own inverse.
Also shift digits — an optional toggle for Caesar and ROT13 that rotates the digits 0 to 9 as well. With ROT13 the digits are rotated by 5 (ROT5), and the combination is commonly called ROT18.

Cracking an unknown shift with brute force

A Caesar cipher has only 25 useful keys, so you do not need to guess. The brute-force table applies every possible shift to your input at once and shows all 25 candidate decryptions, each labelled with its shift. You simply scan the list for the line that reads as ordinary language — the shift on that row is the key that was used. Each row has its own copy button.

This is a complete, exhaustive search rather than a statistical guess, so it always contains the correct answer for any single-shift Caesar (including ROT13). It works on letters only; digits and symbols are left as-is in the table so the words stay readable.

Related terminology

Caesar cipher: A substitution cipher that shifts every letter a fixed number of positions along the alphabet. Named after Julius Caesar, who reportedly used a shift of 3.
Shift (key): The number of positions each letter is moved. For a Caesar cipher it ranges from 1 to 25; ROT13 is the special case of a shift of 13.
ROT13 / ROT47: Fixed-rotation ciphers. ROT13 rotates the 26 letters by 13; ROT47 rotates the 94 printable ASCII characters by 47. Both are their own inverse.
Atbash: A substitution cipher that reverses the alphabet, mapping the first letter to the last (A to Z), the second to the second-last (B to Y), and so on.
Substitution cipher: Any cipher that replaces each character with another according to a fixed rule. Caesar, ROT13, and Atbash are all simple substitution ciphers.
Brute-force attack: Trying every possible key until the plaintext appears. Because a Caesar cipher has only 25 keys, a brute-force attack cracks it almost instantly.

Frequently asked questions

Is the Caesar cipher secure encryption?: No. The Caesar cipher, ROT13, ROT47, and Atbash have no secret key and can be reversed by anyone in seconds — a Caesar shift can even be cracked by trying all 25 keys, which this tool does for you. Use them for puzzles, obfuscation, or hiding spoilers, never to protect sensitive data. For real security use a modern algorithm such as AES.
What is ROT13, and how is it different from ROT47?: ROT13 is a Caesar cipher with a fixed shift of 13 that affects the 26 letters only. ROT47 rotates all 94 printable ASCII characters (codes 33 to 126) by 47, so letters, digits, and punctuation all change. Both are their own inverse, meaning the same operation encodes and decodes.
How do I decode a Caesar cipher if I do not know the shift?: Enable the brute-force table. It lists your text decrypted with all 25 possible shifts at once; read down the rows until one reads as normal language. The shift labelled on that row is the key that was used, and you can copy that line directly.
Does the tool keep capitalization and punctuation?: Yes. In Caesar, ROT13, and Atbash modes, uppercase stays uppercase, lowercase stays lowercase, and spaces, punctuation, and other symbols pass through unchanged. Digits are only altered if you enable the "Also shift digits" option. ROT47 intentionally transforms digits and symbols as well as letters.
What is Atbash?: Atbash is an ancient substitution cipher that mirrors the alphabet: A maps to Z, B to Y, C to X, and so on. It affects letters only and, like ROT13, is its own inverse, so encoding and decoding are the same operation.
Is my text uploaded to a server?: No. All encoding, decoding, and brute-forcing happen entirely in your browser with JavaScript, so your text never leaves your device.

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Caesar Cipher (ROT13)