Caesar Cipher / ROT13
Encode and decode the Caesar cipher. Pick a mode (encrypt / decrypt) and set the shift (1–25) with a slider or number field. One tap sets ROT13 (shift 13). Only A-Z / a-z are rotated; digits, punctuation, spaces, and non-Latin text are left intact. In decrypt mode, a full 25-shift brute-force table is shown to crack ciphertext with an unknown shift. Everything runs in your browser — your input is never uploaded.
How to use
First pick a direction (encrypt / decrypt); switching it updates the placeholder and sample. Set the shift (1–25) with the slider or number field (the 'ROT13' button sets 13 instantly). Type your text and press Convert: only A-Z / a-z are shifted, while digits, punctuation, spaces, and non-Latin text are left unchanged. In decrypt mode a full 25-shift brute-force table appears below the result, so you can crack ciphertext with an unknown shift by scanning for readable rows. Everything runs in your browser.
FAQ
- Is my input uploaded?
- No. All conversion happens in browser JavaScript; your text never leaves your device.
- What is the Caesar cipher?
- One of the oldest ciphers, attributed to Julius Caesar: a substitution cipher that shifts each letter a fixed number of positions. With shift 3, A→D, B→E, and so on. The key is just the shift (1–25), so it's trivial to break and is used today for education, puzzles, and light obfuscation rather than real security.
- What is ROT13?
- A Caesar cipher with the shift fixed at 13. Because the alphabet has 26 letters, shifting by 13 twice returns the original (it's self-inverse), so the same operation both encodes and decodes. It's commonly used to hide spoilers or mask text on forums. The 'ROT13' button sets the shift to 13 instantly.
- Can I crack ciphertext with an unknown shift?
- Yes. In decrypt mode a brute-force table of all shifts 1–25 appears below the result. Since the Caesar cipher has only 25 possible keys, you can always read the plaintext by scanning the rows for one that makes sense.
- What happens to digits, punctuation, and non-Latin text?
- Only Latin letters (A-Z / a-z) are shifted. Digits, punctuation, spaces, and non-Latin characters pass through unchanged — the standard behavior of the classic Caesar cipher.
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