Encrypt and decrypt with Caesar shift cipher. Includes brute-force attack showing all 26 rotations simultaneously.
This tool shifts each letter of the alphabet by a fixed number of positions, wrapping from Z back to A, to encrypt or decrypt text with the classical Caesar cipher. Enter text and a shift value (0-25) to transform it directly, or paste ciphertext with an unknown shift and use brute-force mode, which lists all 26 possible rotations side by side so you can spot the one that reads as plain English. The detail people miss: a shift of 13 is ROT13, and a shift of 0 or 26 returns the original text unchanged.
A concrete input and expected output from the current implementation.
Input
Plaintext: HELLO, shift: 3, mode: encrypt
Expected output
KHOOR
Each letter moves 3 positions forward in the alphabet: H to K, E to H, L to O (twice), and O to R, wrapping past Z if needed.
Each letter's position in the alphabet (A-Z or a-z) is shifted by the chosen amount using modulo-26 arithmetic, so shifting past Z wraps around to A. Non-letter characters such as spaces, digits, and punctuation pass through unchanged, and the original uppercase or lowercase case of each letter is preserved after the shift.
In brute-force mode the tool applies every possible shift from 1 through 25 (plus the unshifted original) to the input text and lists all resulting strings together. Because a Caesar cipher only has 26 possible keys, this exhausts the entire keyspace instantly, letting you scan the list for the row that forms recognizable words.
Yes. Shifting Z forward wraps around to A (and lowercase z wraps to a), and shifting A backward wraps to Z, so the alphabet behaves as a closed 26-letter loop regardless of the shift size or direction you enter.
Yes - that is what brute-force mode is for. It generates all 26 possible rotations of the pasted ciphertext at once, so you read down the list and pick out whichever row forms real words instead of guessing shifts one at a time.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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