Caesar Cipher / ROT13
NewEncode or decode text with a Caesar cipher shift (including ROT13), with all 25 possible shifts shown for brute-forcing an unknown key.
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Only letters A-Z/a-z are shifted; digits, punctuation, and spaces pass through unchanged. ROT13 is simply a Caesar cipher with a fixed shift of 13, which is its own inverse (applying it twice returns the original text).
Frequently Asked Questions
What is ROT13 exactly?
ROT13 ("rotate by 13") is a Caesar cipher with a fixed shift of 13. Because the alphabet has 26 letters, applying the same 13-shift twice returns the original text — which is why ROT13 is popular for lightly obscuring spoilers or answers rather than genuine encryption.
Is this cipher actually secure?
No — Caesar ciphers (including ROT13) offer no real security. With only 25 possible shifts, they can be broken instantly by brute force or letter-frequency analysis, which is exactly what the "all 25 shifts" panel in this tool demonstrates.
What happens to numbers and punctuation?
Only letters A-Z and a-z are shifted; digits, spaces, and punctuation pass through completely unchanged, matching the traditional definition of the Caesar cipher.
How do I decode a message with an unknown shift?
Paste the ciphertext and scan the "all 25 shifts" list below the main result — the correct shift is whichever one produces readable text, since a genuine Caesar cipher has no larger keyspace to search.
Does a negative shift value work?
Yes — a negative shift is normalized (via a modulo-26 wraparound) to its equivalent positive shift, so shifting by -3 behaves identically to shifting by 23.