Caesar Cipher & ROT13 – Free Online Shift Encoder/Decoder Tool
Encode or decode any text using the Caesar cipher — the classic letter-substitution cipher used since ancient Rome. Choose any shift from 1 to 25, use the ROT13 preset (shift 13), or let the brute-force tab reveal all 25 possible rotations side by side for unknown ciphertexts. Preserves letter case, leaves numbers and symbols unchanged. Perfect for learning cryptography, hiding spoilers, and solving puzzles. No login or installation required.
Mode
Shift valueROT13
Presets
Options
How to Use the Caesar Cipher Tool
How to Use the Caesar Cipher ToolWhat is the Caesar Cipher?
The Caesar cipher is one of the oldest and simplest encryption techniques, attributed to Julius Caesar. It substitutes each letter with another letter that is a fixed number of positions ahead in the alphabet. For example, with a shift of 3: A→D, B→E, Z→C. Numbers, spaces, and symbols are left unchanged.
ROT13 — the internet standard:
ROT13 is Caesar with shift = 13. Because the English alphabet has 26 letters, applying ROT13 twice returns the original text — making it self-inverse (encode = decode). ROT13 is widely used on forums and social media to hide spoilers. Example: Hello → Uryyb → back to Hello.
Features:
- Shift 1–25: Use the +/− buttons, type a number, or pick a preset (ROT1, ROT5, ROT13, ROT18, ROT25).
- Encode / Decode: Toggle between forward and reverse shift.
- Preserve case: Keeps uppercase letters uppercase and lowercase lowercase.
- Alphabet mapping: A live table shows exactly which letter maps to which for your chosen shift.
- Brute Force tab: Input unknown ciphertext to instantly see all 25 possible rotations side by side — click "Use →" on any row to apply that shift in the Cipher tab.
