Encrypt and decrypt text using the Caesar cipher with shift selection and brute-force decryption display.
A Caesar cipher replaces every letter with the letter a fixed number of positions further along the alphabet, so with shift 3, HELLO becomes KHOOR. This tool applies that shift in either direction and, when you do not know the shift, displays all 26 possible decryptions side by side for you to pick the readable one. The surprise for most first-time users is that this cipher is not any kind of security: with only 25 nontrivial shifts, every Caesar message is trivially recoverable, and the brute-force view makes that visible in one glance.
A concrete input and expected output from the current implementation.
Input
HELLO WORLD, shift 3, Encrypt
Expected output
KHOOR ZRUOG
Each letter advances three places and wraps past Z, so H becomes K, E becomes H, L becomes O, O becomes R, W becomes Z, and D becomes G; spaces pass through unchanged. Decrypting with shift 3, or the shift-3 row of the brute-force table, restores HELLO WORLD.
Encrypting adds the shift to each letter's position in the alphabet (A = 0 through Z = 25), and any total past 25 wraps around to the start, so with shift 3 the letter Z becomes C. Decrypting subtracts instead. Letters keep their case, digits and punctuation pass through untouched, and only a-z letters move.
Brute-force mode runs the text through every shift from 1 to 25 (plus shift 0, the unchanged original) and lays the results out as a table, so one row is always the real message. That row stands out by eye because a real sentence reads naturally while the other 25 rows are usually gibberish. Longer, phrase-like messages make the readable row unmistakable.
No. With only 25 possible shifts, trying every shift takes seconds and the table always contains the real message. There is no key in the modern sense: anyone who knows the method can read the text, and brute-force mode exists precisely because of that. Use it for puzzles, teaching, or casual obfuscation, never for anything that should stay private.
Shift 13 is ROT13. Because the alphabet has 26 letters, shifting by 13 pairs each letter with the one halfway round: A pairs with N, B with O, and so on. Applying it twice returns the original text, which makes it handy for hiding spoilers or puzzle answers: the reader just runs the same shift again, with no direction to remember.
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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