ROT13 decoder and encoder, free and private
To decode ROT13 for free, paste the text into the Input Text box with ROT13 selected under Rotation Type. The decoded text appears under Output straight away. ROT13 is its own inverse, so the same step encodes and decodes: run encoded text through it a second time and the original comes back. Nothing leaves your browser, and the Network tab in DevTools shows no request while you type.
ROT13 is a letter substitution cipher that replaces each letter with the one 13 places further along the alphabet, wrapping from Z back to A. The formula is new position = (old position + 13) mod 26, with A as 0 and Z as 25. Because the alphabet has 26 letters, two steps of 13 make one full circle. Digits, punctuation, spaces and accented letters stay as they are.
ROT13 is not encryption. It has no key and only 25 shifts exist, so it only keeps a spoiler or a puzzle answer out of sight until someone chooses to decode it. For real protection use the text encryption tool and its matching text decryption tool.
Table of Use: settings, inputs and outputs
Each row shows a Rotation Type, what you paste in and what you get back.
| Task | Setting | Input | Output |
|---|---|---|---|
| Decode a hidden spoiler | ROT13 | Gur ohgyre qvq vg | The butler did it |
| Encode a message | ROT13 | Hello World | Uryyb Jbeyq |
| Scramble digits only | ROT5 | 12345 | 67890 |
| Scramble letters and digits | ROT18 | Room 101 | Ebbz 656 |
| Scramble every printable ASCII character | ROT47 | Hello World! 123 | w6==@ (@C=5P `ab |
| Encode with a Caesar shift of 3 | Custom (Caesar), shift 3, Encode (shift forward) | Attack at dawn | Dwwdfn dw gdzq |
| Decode a Caesar message | Custom (Caesar), shift 3, Decode (shift back) | Dwwdfn dw gdzq | Attack at dawn |
| Output in capitals | ROT13 with "Keep letter case" unticked | Hello | URYYB |
| Text with an accent | ROT13 | café | pnsé (the é is not a plain letter, so it stays) |
Features
- Five Rotation Types. ROT13, ROT5, ROT18, ROT47 and Custom (Caesar), each with a one-line description under the buttons.
- Any Caesar shift. Set a shift from 1 to 25 with the slider or the number box and choose Encode (shift forward) or Decode (shift back). Decoding a shift of n equals encoding with 26 minus n.
- Swap. Moves the output into the input. ROT13, ROT5, ROT18 and ROT47 undo themselves; for a Caesar shift the direction flips, so the original text comes back.
- Keep letter case. Ticked by default for ROT13, ROT18 and Custom. Untick it to get capitals.
- Only the right characters change. Letters A-Z and a-z, digits for ROT5 and ROT18, and printable ASCII for ROT47. Spaces, accents, emoji and other alphabets pass through.
- Copy and Download .txt. The file is named after the setting, such as rot13-output.txt or rot3-encoded-output.txt. A character count sits under both the input and the output.
- Reset. Clears the text and returns to ROT13, a shift of 3, Encode and Keep letter case.
ROT13 is one of several simple text encodings. Others on this site include the Base64 encoder with its Base64 decoder, the Morse code translator and the binary to text converter.
How to Use the ROT13 Encoder and Decoder
- Type or paste your text into Input Text.
- Under Rotation Type choose ROT13 (selected to begin with), ROT5, ROT18, ROT47 or Custom (Caesar).
- For Custom (Caesar), pick the shift with the slider or number box, then choose Encode (shift forward) or Decode (shift back).
- Read the result under Output and the Note in the blue box, which explains how to decode it.
- Click Copy or Download .txt. Click Swap to run the output through the cipher again, or Reset to start over.
Who Can Use It
Forum readers and writers hide spoilers and punchlines. Puzzle fans and geocachers decode hint text. Students meet the Caesar cipher in cryptography lessons and can step the slider through all 25 shifts to see why it is easy to break.
Developers and CTF beginners use ROT13 and ROT47 to spot or test light obfuscation, and can reverse a word or phrase afterwards with the string reverser, turn it into numbers with the text to ASCII converter, or fix capitals with the text case converter.
FAQs
How do I decode ROT13 online?
Paste the encoded text into the Input Text box and keep ROT13 selected under Rotation Type. The decoded text appears under Output straight away. ROT13 is its own inverse, so there is no separate decode setting: the same operation that encodes a message also decodes it. Click Copy to take the result, or Swap to run the output through ROT13 again.
What is ROT13 and how does it work?
ROT13, short for "rotate by 13 places", is a letter substitution cipher. Each letter is replaced by the letter 13 positions further along the alphabet, wrapping from Z back to A, so A becomes N and N becomes A. Digits, punctuation, spaces and accented letters are left alone. The formula is new position = (old position + 13) mod 26, counting A as 0.
What is the difference between ROT13 and a Caesar cipher?
ROT13 is a Caesar cipher with the shift fixed at 13. A Caesar cipher can shift letters by any amount from 1 to 25, and Julius Caesar is reported to have used 3. Only a shift of 13 is its own inverse on a 26-letter alphabet. For other shifts you must shift back, which Custom (Caesar) does when you choose Decode (shift back).
How do I decode a Caesar cipher when I do not know the shift?
Choose Custom (Caesar), set the direction to Decode (shift back) and move the slider through the shifts from 1 to 25. The output updates with every step, so you can stop when the text becomes readable. There are only 25 possibilities, which is why a Caesar cipher is easy to break. The Note under the options shows the matching ROT value.
Is ROT13 encryption, and is it secure?
No. ROT13 is obfuscation, not encryption. It has no key, there are only 25 possible shifts and letter frequencies stay the same, so anyone can reverse it in seconds. It is meant for hiding spoilers, punchlines and puzzle answers from a casual glance. For text that really must stay private, use the text encryption tool, which protects it with a password.
What are ROT5, ROT18 and ROT47, and which should I use?
ROT5 rotates only the digits 0-9 by five places. ROT18 applies ROT13 to letters and ROT5 to digits in one step. ROT47 rotates all 94 printable ASCII characters from ! to ~ by 47 places, so punctuation changes as well. Use ROT13 for text, ROT5 for numbers, ROT18 for both, and ROT47 when symbols should be scrambled too. All four undo themselves.
Why are my numbers, accents or emoji not changed?
ROT13 and the Caesar cipher only move the English letters A to Z and a to z, so digits, accented letters such as é, other alphabets and emoji pass through untouched. Use ROT5 or ROT18 to rotate digits. ROT47 changes only printable ASCII characters and also leaves anything outside that range alone, so no emoji are ever split or damaged.
Is my text sent anywhere when I use the ROT13 tool?
No. The rotation runs as JavaScript in your browser and nothing you type is uploaded to ZipConvert or anyone else. You can confirm it in the Network tab of DevTools, where no request appears as you type. Nothing is stored, so closing or refreshing the tab clears the text. Keep in mind that ROT ciphers do not protect data.