Encrypt or decrypt text with Caesar cipher or ROT13 instantly using this free online tool. Shift letters by any amount (1-25) to encode or decode messages. Perfect for learning cryptography, creating puzzles, or encoding spoilers. No installation needed—easy, fast Caesar cipher and ROT13 encoding for any text.

Caesar Cipher / ROT13

Cipher Type

ROT13 (fixed shift) Caesar Cipher (custom shift)

Input

Output

How to Use the Caesar Cipher & ROT13 Converter

Operation options:

ROT13:
Applies a fixed shift of 13 positions to each letter.
Letters A–M map to N–Z, and N–Z map back to A–M. Non-letters remain unchanged.
Custom Caesar Cipher:
Enter a shift key (1–25). Each letter in your text is shifted by that key.
For example, with shift 3, A→D, B→E, …, X→A, Y→B, Z→C.

How to use:

Paste or type your text into the Input area.
Select ROT13 or Custom Caesar Cipher.
If using Custom Caesar, enter a shift key between 1 and 25.
Your encoded or decoded result appears instantly in the Output area.
Use Copy to copy the result, or Clear to reset and start over.

Tips:

Non-alphabetic characters (digits, punctuation, spaces) are not changed.
Case is preserved: lowercase stays lowercase, uppercase stays uppercase.
ROT13 is a special case of Caesar Cipher with a fixed shift of 13.
For military or puzzle use, choose a shift key that is hard to guess.