Encode and decode Caesar, ROT13 and Atbash ciphers, with a brute-force panel that ranks all 25 shifts by how English each result reads. Free.
First time here? Pick Caesar, ROT13 or Atbash Your input is processed locally and disappears when you close the tab.
A Caesar cipher shifts every letter a fixed number of places along the alphabet. It is roughly two thousand years old, trivially breakable, and still turns up constantly in puzzles, CTF challenges, escape rooms and homework. This free caesar cipher decoder handles it in both directions.\n\nThe useful part is the brute-force panel. Because there are only 25 possible shifts, you never actually need the key — the tool tries every one and ranks the results by how much like English each reads, scoring against common words. The correct answer is almost always at the top, and one click applies that shift.\n\nROT13 is included as a preset: a Caesar shift of 13, which is exactly half of 26 and therefore its own inverse. That is why it has been used for decades to hide spoilers and punchlines — applying it again undoes it. Atbash reverses the alphabet instead, mapping A to Z and B to Y, and is likewise self-inverse with no key at all.\n\nNone of this is security, and the brute-force panel is the clearest possible demonstration of why. Numbers, punctuation and case all pass through untouched so the shape of the message survives. For anything you actually need to keep private, use the AES Text Encryption tool instead.
Pick Caesar, ROT13 or Atbash
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Set the shift, or tick decode to brute force it
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These are puzzles, not security. A Caesar cipher has 25 possible keys and can be broken by hand in under a minute — the brute-force panel above does exactly that. ROT13 is Caesar with a shift of 13, which makes it its own inverse. Atbash reverses the alphabet and has no key at all. For anything that actually needs protecting, use the AES encryption tool.