ROT13 / Caesar Cipher

Encode & Decode with a Letter Shift

Text

Shift Amount: 13

Result

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Understanding the Caesar Cipher & ROT13

Letter Substitution

Each letter is replaced by the one a fixed number of positions later in the alphabet, wrapping from Z back to A.

ROT13 Is Self-Inverse

With a shift of exactly 13, applying the cipher twice returns the original text — encode and decode are the same operation.

Spoiler Obfuscation

ROT13 is still used on forums and Usenet to hide spoilers or puzzle answers from a casual glance.

Local Processing

The shift is applied entirely in your browser — nothing is sent to a server.

Not a Security Tool

The Caesar cipher is one of the oldest and weakest ciphers in history — with only 25 possible shifts, it can be broken by hand in seconds or by brute force instantly. Use it for puzzles, obfuscating spoilers, or learning about cryptography basics, never for protecting sensitive information.

Key Takeaways

Letters Only: Numbers, punctuation, and spaces pass through unchanged.
Case Preserved: Uppercase and lowercase letters shift independently, keeping their case.
Client-Side Only: All processing happens locally in your browser.

ROT13 / Caesar Cipher Encoder & Decoder Online