ROT13 Cipher

Apply the ROT13 substitution cipher to text — rotating each letter by 13 positions in the alphabet.

ROT13 Cipher

Apply ROT13 transformation to text. Run twice to decode ROT13-encoded text.

Input Text

ROT13 Output

💡 About ROT13 Cipher

ROT13 is a simple letter substitution cipher that shifts each letter 13 positions in the alphabet.

Key features:

Symmetric: Applying ROT13 twice returns original text
Case-preserving: Uppercase stays uppercase, lowercase stays lowercase
Letters only: Numbers, spaces, and symbols remain unchanged
Historical use: Common in online forums for spoiler protection

Example: "Hello World" → "Uryyb Jbeyq"

⚠️ Security Note: ROT13 is NOT secure encryption—it's easily broken and should only be used for obfuscation.

What is ROT13?

ROT13 ("rotate by 13 places") is a simple letter substitution cipher that replaces each letter with the letter 13 positions ahead of it in the English alphabet. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — encoding and decoding are the same operation.

Only letters are transformed; digits, punctuation, and spaces pass through unchanged. ROT13 is not a secure cipher and provides no real confidentiality — it is intended purely for obfuscation.

Common Use Cases

Spoiler Hiding: Online forums and communities use ROT13 to obscure plot spoilers so readers must actively choose to decode them. Puzzle and CTF Challenges: ROT13 is a staple obfuscation technique in beginner-level Capture the Flag security competitions. Obfuscating Email Addresses: Lightweight obfuscation of email addresses in plain-text to deter simple scraper bots, though it is easily bypassed. Teaching Cryptography Concepts: ROT13 is an approachable introduction to substitution ciphers and the concept of symmetric key operations.

Tips

ROT13 is self-inverse — running it a second time on any ROT13 output always recovers the original plaintext. Case is preserved during transformation: uppercase letters rotate within A–Z, and lowercase letters rotate within a–z. Never use ROT13 for security-sensitive purposes; it provides zero cryptographic protection and is instantly reversible by anyone.