ROT13 Cipher
Encode and decode text with the ROT13 / Caesar cipher
ROT13 (shift 13) is its own inverse — the same operation encodes and decodes. To undo shift N, use shift 13.
Plaintext / Ciphertext
Result (shift 13)
About
Apply the ROT13 cipher (or any Caesar shift from 1 to 25) to text. ROT13 is its own inverse, so the same operation encodes and decodes. Letter case is preserved and non-letters are left untouched. Everything runs in your browser; nothing is uploaded.
Examples
ROT13 encode 'Hello'
text: HellouryybH → U, e → r, l → y, l → y, o → b. Encoding twice: URYYB → HELLO, confirming it is self-inverse.
Caesar shift of 3
text: Attack at dawn
shift: 3DWWDFN DW GDZQA → D, T → W, C → F, K → N. Spaces and case are preserved; non-letters pass through unchanged.
About this tool
ROT13 (Rotate by 13 places) is a Caesar cipher — a simple substitution where each letter is replaced by the one 13 positions ahead in the alphabet. The key property of ROT13 is that it is its own inverse: applying ROT13 twice returns the original text. This makes it a quick, reversible scrambling method without the complexity of a key.
ROT13 is commonly used on the internet to hide spoilers, solutions, punchlines, and offensive content — anyone who wants to read it simply applies ROT13 again. This tool lets you encode and decode with an adjustable shift (0–25), so you can experiment with Caesar ciphers beyond ROT13.
How to use
Choose a shift or use ROT13
ROT13 (shift = 13) is the default and is its own inverse. Adjust the shift slider to any value 0–25 for a general Caesar cipher.
Enter your text
Type or paste the text you want to encode. Non-letters (digits, punctuation, spaces) are passed through unchanged.
Copy the result
Click Copy to grab the shifted output. Apply the same shift again to decode.
Use cases
Hiding spoilers in a forum post
Paste text, apply ROT13, and share the result. Readers who want the surprise can apply ROT13 again to decode it.
Learning about substitution ciphers
Adjust the shift value to see how the Caesar cipher behaves at different key values, or use the frequency chart from the Character Frequency tool alongside this one.
Simple obfuscation for puzzles
Create a quick puzzle by encoding a clue with ROT13 and sharing it without giving away the answer.
Common mistakes
Mistake:Forgetting that ROT13 is case-preserving.
Fix:A uppercase letter stays uppercase, a lowercase stays lowercase. 'A' with shift 13 wraps to 'N' (not 'n').
Mistake:Applying ROT13 to non-Latin alphabets.
Fix:ROT13 operates on the 26 Latin letters A–Z only. Characters outside that range (accented letters, Cyrillic, Chinese) are passed through unchanged, which may expose them unintentionally.
Mistake:Using ROT13 for actual security.
Fix:ROT13 provides no cryptographic security — it is trivial to break with a frequency analysis. It is obfuscation at best, not encryption. Use AES or ChaCha20 for real data protection.
Frequently asked questions
Related guides
Caesar Ciphers, ROT13, and Why Neither Is Encryption
What a shift cipher is, why ROT13 is self-inverse and useful for light obfuscation, and how frequency analysis breaks even large keys efficiently.
Letter Frequency Analysis: How Frequency Stats Crack Substitution Ciphers
What the letter distribution in English looks like, how to use it to break a Caesar cipher, and what word and line stats reveal that individual letters miss.
References & standards
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