What Is ROT13?
ROT13 (“rotate by 13 places”) is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Since there are 26 letters, applying ROT13 twice returns the original text — making it both the encoder and the decoder.
ROT13 is not encryption — it provides no real security. It's used to obscure text so it can't be read at a glance, such as hiding spoilers, puzzle answers, or punchlines. This tool runs entirely in your browser — no text is sent to any server.
How to Use This Tool
Enter Your Text
Type directly into the input editor, paste content with Ctrl+V, or upload/drag a .txt file.
See ROT13 Output
The encoded (or decoded) text appears instantly in the right panel. ROT13 works both ways — encoding and decoding are the same operation.
Copy or Download
Use Copy to copy the ROT13 output to clipboard, Download to save as a .txt file, or Clear to reset.
Decode ROT13 Text
To decode, simply paste ROT13-encoded text into the input — the output will be the original plain text.
Features Explained
Self-Inverse Cipher
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ROT13 is its own inverse. Applying it once encodes the text; applying it again decodes it. This means the same tool works for both encoding and decoding — no mode switch needed.
Preserves Non-Letters
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Numbers, spaces, punctuation, and special characters pass through unchanged. Only the 26 English letters (A–Z, a–z) are rotated. Case is preserved — uppercase stays uppercase, lowercase stays lowercase.
Real-Time Processing
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The output updates instantly as you type. The computation is memoized for performance, so only changes to the input trigger recalculation.
File Upload & Drag and Drop
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Upload a .txt file using the Upload button or drag and drop a text file directly onto the input area. The file contents replace the current input text.
Who Is This Tool For?
Forum Users
Hide spoilers, puzzle answers, or punchlines in online forums and message boards where ROT13 is a common convention.
Developers
Test encoding functions, obfuscate sample data, or work with APIs and systems that use ROT13 for light obfuscation.
Puzzle Enthusiasts
Encode and decode clues, hints, and answers for puzzles, geocaching, and escape room challenges.
Educators
Teach basic cryptography concepts using ROT13 as a simple, hands-on introduction to substitution ciphers.
Email Users
Lightly obscure sensitive words in emails or messages so they aren't immediately readable at a glance.
Students
Learn about cipher fundamentals, modular arithmetic, and the history of cryptography through a practical example.
ROT13 Alphabet Mapping
| 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ROT13 | 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 |
Each letter maps to the letter 13 positions ahead: A↔N, B↔O, C↔P, and so on. The mapping is symmetric.
Tips for Using ROT13
ROT13 is not encryption
Never use ROT13 to protect sensitive information. It's trivially reversible and provides no security — it's only meant to obscure text from casual reading.
Encode and decode are the same
You don't need to select a mode. Paste plain text to encode it, or paste ROT13 text to decode it. The operation is identical both ways.
Use for spoiler protection
The most common use of ROT13 is hiding spoilers in forums, newsgroups, and online communities. Readers must actively decode to see the content.
Numbers and symbols stay unchanged
ROT13 only affects the 26 English letters. Numbers, punctuation, spaces, and special characters are preserved exactly as entered.
Try double-encoding to verify
Paste your ROT13 output back into the input — you should get your original text back. This is a quick way to verify the cipher is working.
Works with any length
ROT13 processes each character independently, so it works the same whether you have a single word or an entire document.
Privacy & Security
This tool runs 100% in your browser. Your text is never uploaded to any server. It is stored only in your browser's local storage so it persists when you refresh the page.
You can clear it at any time using the “Clear” button. No cookies are used, no analytics track your text content, and no third-party services have access to what you type.