ROT13 Encoder / Decoder

Encode or decode text using the ROT13 cipher. Apply it twice to get the original text back.

Free to use. Runs in your browser.

Paste text to apply the ROT13 Caesar cipher, each letter is shifted 13 places. Applying ROT13 twice returns the original text. Commonly used for spoilers and puzzle answers.

ROT13 only changes English letters A to Z. Numbers, punctuation, spaces, emoji, and non-Latin characters pass through unchanged.

Input

ROT13 Output

How it works: Each letter is shifted 13 positions in the alphabet. Since there are 26 letters, applying ROT13 twice returns the original text. Numbers and special characters are unchanged.

Good to know before using ROT13

ROT13 is reversible text obfuscation. It is useful when the reader is allowed to reveal the message, not when the message needs protection.

Encode and decode are identical

Paste ROT13 output back into the tool and you get the original text.

Case is preserved

Hello becomes Uryyb, keeping the capital H pattern.

It is not encryption

Anyone can reverse ROT13 by applying the same shift again. Do not use it for secrets.

Non-letters stay visible

Dates, numbers, punctuation, and URLs remain readable, which can be useful or revealing.

English alphabet only

Accented letters such as é and non-Latin scripts are left as they are.

Useful for reversible hints

ROT13 works well for puzzle nudges and spoilers where the reader can choose to reveal the text.

URLs stay mostly readable

The punctuation in https:// remains, so ROT13 is a poor fit for hiding links.

Short text may be obvious

Words such as "uryyb" are recognisable ROT13 patterns to many puzzle solvers.

Apply twice to test

A quick sanity check is to paste the output back in and confirm the original text returns.

For anything sensitive, use real encryption with keys instead of a reversible alphabet shift.

ROT13: The Simplest Cipher

ROT13 is a letter substitution cipher that replaces each letter with the one 13 positions later in the alphabet. A becomes N, B becomes O, C becomes P, and so on. Since the English alphabet has 26 letters, applying ROT13 twice gives you back the original text, it's its own inverse.

ROT13 isn't encryption, it provides zero security against anyone who knows what it is (which is everyone). It's a spoiler tag for text. Usenet newsgroups used it in the 1980s and 90s to hide punchlines, puzzle solutions, and movie spoilers. Today you'll still see it used in forums, CTF challenges, and as the canonical example of a Caesar cipher in computer science courses.

The beauty of ROT13 is its symmetry: encode and decode are the same operation. Paste encoded text, get the original. Paste plain text, get the encoded version. The same button does both.

ROT13 Alphabet Mapping

Original	A-M	N-Z
Input	A B C D E F G H I J K L M	N O P Q R S T U V W X Y Z
Output	N O P Q R S T U V W X Y Z	A B C D E F G H I J K L M

What this means for you: Each letter swaps with its partner 13 positions away. A↔N, B↔O, C↔P... The mapping is perfectly symmetrical, which is why encoding equals decoding. Numbers, spaces, and punctuation are unchanged.

Caesar Ciphers and ROT Variants

Cipher	Shift	"HELLO" Becomes	Used For
ROT1	1	IFMMP	Educational examples
ROT3	3	KHOOR	Original Caesar cipher
ROT5	5 (digits only)	N/A (affects 0-9)	Obscuring phone numbers
ROT13	13	URYYB	Text spoiler hiding (self-inverse)
ROT47	47 (ASCII 33-126)	w6{{~	Obscuring all printable ASCII

What this means for you: ROT13 is special because 13 is exactly half of 26 (the alphabet size), making it self-inverse. No other ROT value has this property for the English alphabet. ROT47 extends the concept to all printable ASCII characters.

Where You'll Encounter ROT13

CTF challenges

Capture The Flag competitions frequently use ROT13 as a warm-up challenge or as one layer in a multi-step decoding puzzle. If you see text that looks like garbled English, try ROT13 first, it's the most common simple encoding in CTFs.

Forum spoiler tags

Before HTML spoiler tags existed, Usenet and early forums used ROT13 to hide spoilers. You had to deliberately decode the text to read it. The convention persists in some communities and mailing lists.

Programming interviews

Implementing ROT13 is a classic interview question that tests string manipulation, character codes, and modular arithmetic. The one-liner version in most languages is surprisingly elegant.

Email address obfuscation

Some websites encode email addresses with ROT13 in HTML to deter simple spam bots, then decode them with JavaScript when displayed. It only blocks the simplest copy-paste scraping, and modern bots can still read it.

ROT13 One-Liners by Language

Language	Implementation
JavaScript	s.replace(/[a-z]/gi, c => String.fromCharCode(c.charCodeAt(0) + (c.toLowerCase() < 'n' ? 13 : -13)))
Python	import codecs; codecs.encode(s, 'rot_13')
Bash	echo "text" \| tr 'A-Za-z' 'N-ZA-Mn-za-m'
Ruby	s.tr('A-Za-z', 'N-ZA-Mn-za-m')
PHP	str_rot13($s)

Python and PHP have built-in ROT13 functions, that's how common it is. The Bash tr approach is the classic Unix way and works in any terminal.

Worked ROT13 Example

A puzzle setter might hide a hint with ROT13 so the reader can choose whether to reveal it:

Plain text

Check the left door first.

ROT13 text

Purpx gur yrsg qbbe svefg.

Paste the ROT13 text back into the encoder and it returns the original sentence. The full stop and spaces are unchanged.

Common ROT13 Mistakes

Calling it secure

ROT13 is intentionally easy to reverse. It hides casual spoilers, not private information.

Expecting punctuation to change

Only letters A to Z are shifted. Numbers, punctuation, whitespace, and symbols stay in place.

Forgetting that case is preserved

Uppercase input stays uppercase after the shift, and lowercase input stays lowercase.

Using it for non-English alphabets

ROT13 is defined around the 26-letter English alphabet. Other scripts need different rules.

Related Tools

Binary Text Converter

Convert text to binary encoding

Morse Code Translator

Encode text as dots and dashes

Base64 Encoder

Encode data in Base64 format

Hash Generator

One-way cryptographic hashing

Password Generator

Generate secure passwords

Case Converter

Transform text case

How to use this tool

Paste or type text in the input panel

The ROT13 output appears instantly in the right panel

Paste ROT13 text to decode it, encoding and decoding are the same

Common uses

Hiding spoilers in text-based forums and messages
Solving CTF and puzzle challenges
Learning about substitution ciphers in CS courses
Obfuscating text in a reversible, recognisable way

Share this tool

Frequently Asked Questions

What is ROT13?

ROT13 is a letter substitution cipher that shifts each letter 13 positions in the alphabet. A becomes N, B becomes O, and so on. Since the alphabet has 26 letters, applying ROT13 twice gives you back the original text, encoding and decoding are the same operation.

Is ROT13 secure?

No. ROT13 provides zero security, it's trivially reversible by anyone who knows what it is (which is everyone in tech). It's an obfuscation tool, not encryption. Think of it as putting a spoiler behind a curtain, not locking it in a safe.

Is my text sent to a server?

No. The conversion uses a simple character-by-character JavaScript function in your browser after the page loads. Nothing is transmitted, stored, or logged by the converter.

Why is ROT13 special among Caesar ciphers?

Because 13 is exactly half of 26 (the English alphabet size). This makes it self-inverse, the same function encodes and decodes. No other shift value has this property. ROT1 encoding needs ROT25 to decode; ROT13 needs just ROT13 again.

What happens to numbers and punctuation?

They're unchanged. ROT13 only affects letters A-Z and a-z. Numbers, spaces, punctuation, and symbols pass through unmodified. This is standard for all ROT13 implementations.

Where is ROT13 actually used?

Historically, Usenet newsgroups used it for spoiler text. Today it appears in CTF (Capture The Flag) competitions, programming puzzles, email obfuscation, and as the go-to example of a Caesar cipher in computer science courses.

What's a Caesar cipher?

A substitution cipher that shifts letters by a fixed number. Named after Julius Caesar, who reportedly used a shift of 3 (A→D, B→E). ROT13 is a Caesar cipher with shift 13. All Caesar ciphers are trivially breakable, there are only 25 possible shifts to try.

Can I decode text I didn't encode?

If you suspect text is ROT13 encoded, paste it in. If it becomes readable English, it was ROT13. If it stays garbled, it's encoded with something else (or it's not English). The reversible nature of ROT13 means you can always try it non-destructively.

How is ROT13 implemented in code?

The one-liner in most languages maps each letter through the 13-shift. In JavaScript: text.replace(/[a-zA-Z]/g, c => String.fromCharCode((c <= 'Z' ? 90 : 122) >= (c.charCodeAt(0) + 13) ? c.charCodeAt(0) + 13 : c.charCodeAt(0) - 13)). It's a classic interview question.

What's ROT47?

ROT47 extends the concept to all printable ASCII characters (94 characters from ! to ~), shifting by 47. It encodes numbers and symbols too, not just letters. 'Hello 123!' becomes 'w6==~ `abP'. More comprehensive than ROT13 but less commonly used.

Is ROT13 case-sensitive?

ROT13 preserves case. Uppercase A-M maps to N-Z (and vice versa). Lowercase a-m maps to n-z (and vice versa). 'Hello' becomes 'Uryyb', the capitalisation pattern is maintained.

Why do I see ROT13 in CTF competitions?

CTF challenges use ROT13 as a warm-up or as one layer in multi-step decoding puzzles. If you encounter text that looks like garbled English (recognisable word patterns but wrong letters), try ROT13 first, it's the most common simple encoding in CTF events.

Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.