Shift cipher with encrypt/decrypt and brute force. Free, private, runs in your browser.
100% private — your files never leave your browser. All processing happens locally on your device.
The Caesar cipher is named for Julius Caesar, who reportedly used a shift of 3 to protect military correspondence. Each letter in the plaintext is replaced by the letter that many positions later in the alphabet — so with shift 3, A becomes D, B becomes E, and Z wraps around to C.
With only 25 possible keys, the Caesar cipher is trivially broken by exhaustive search. Every modern computer and every phone can try all shifts in a fraction of a second and let you visually identify the plaintext. Use it for puzzles, education, escape-room clues, or light obfuscation — never for real secrets.
Switch direction to flip between encryption and decryption. With the same shift, 'Decrypt' reverses 'Encrypt' exactly. Case is preserved, and non-alphabetic characters — digits, spaces, punctuation — pass through unchanged so the message structure remains legible.
The brute-force panel shows all 25 possible decryptions of an unknown ciphertext. Educators use this to demonstrate why single-substitution ciphers fail: no matter how secret the shift was, anyone with a few seconds can break it. It's a powerful motivator for understanding why modern symmetric ciphers like AES exist.
A substitution cipher where each letter is shifted by a fixed number of positions in the alphabet. Attributed to Julius Caesar, who reportedly used a shift of 3 to protect military messages.
No — it's trivially broken by trying all 25 possible shifts. Use only for puzzles, education, or low-stakes obfuscation. For real security, use modern AES encryption.
Switch direction to 'Decrypt' and enter the same shift the encrypter used. The tool reverses the transformation automatically.
It renders all 25 possible decryptions simultaneously so you can visually scan for the one that reads as English (or any natural language). It's the standard way to crack a Caesar cipher without knowing the shift.