Caesar Cipher (ROT13)
Last updated: June 24, 2026Encode and decode shifted text.
Caesar Cipher (ROT13) is a free online tool to encode and decode shifted text. It runs entirely in your browser, so your files never leave your device — nothing is uploaded. There's no sign-up, no watermark, and it works on any modern browser on desktop or mobile.
How to use Caesar Cipher (ROT13)
The Caesar Cipher tool encodes and decodes text by shifting each letter a fixed amount, including the classic ROT13. Numbers, spaces and punctuation are left unchanged. Free, instant and runs in your browser.
Read the full guide: Caesar Cipher: Encode & Decode Text Online (ROT13)
- 1Choose Encode or Decode and set the shift.
- 2Enter your text (or tap ROT13).
- 3Copy the result.
Any shift + ROT13
Use any shift 0–25, or one-tap the classic ROT13.
Both directions
Encode a message or decode one you received.
Free & private
Runs on your device with no sign-up.
Hide spoilers and puzzle answers with ROT13
ROT13 is the internet's standard way to mask spoilers, riddle answers, and joke punchlines so nobody reads them by accident. Tap the ROT13 button, paste your spoiler, and post the scrambled output to a forum, Reddit thread, or Discord. Because shift 13 is symmetric, readers run the same text back through this tool to reveal it, no separate key needed.
Teach a cryptography lesson in class
Students learning how substitution ciphers work can encode a message with shift 3, the historical Caesar cipher, then watch a classmate decode it with the matching shift. Set any value from 0 to 25 to compare results, see how letters wrap from Z back to A, and notice that spaces and punctuation stay readable. It makes a clear, hands-on demo for a beginner cryptography or computer science lesson.
Crack a cipher with an unknown shift
Received scrambled text but don't know the shift used to encode it? Switch to Decode and step the shift through 1 to 25, checking each result until readable words appear, a quick manual brute force since there are only 25 possibilities. The tool decodes instantly as you change the number, so you can scan every option in seconds and recover the original message.
Caesar Cipher (ROT13) — frequently asked questions
What is a Caesar cipher?
A simple substitution cipher that shifts every letter by a fixed number of places in the alphabet. A shift of 13 is ROT13.
How do I decode a Caesar cipher?
Switch to Decode and enter the same shift used to encode it — the tool reverses the shift.
Is it free?
Yes, completely free.
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