Caesar Cipher and ROT13 Tool
Shift every letter of your message by a chosen number of places to encrypt it, or shift it back to decrypt. Use the ROT13 button for the classic 13-place shift, and open the table of all 25 shifts to break a Caesar message when you do not know the key. Nothing leaves your browser.
Runs in your browser. Your files are never uploaded.
Loading Caesar Cipher and ROT13 Tool…
How to use Caesar Cipher and ROT13 Tool
- Choose Encrypt or Decrypt and type or paste your text.
- Move the slider to set the shift from 1 to 25, or press ROT13.
- Read the result and press Copy.
- To crack a message with an unknown shift, open the table of all 25 shifts and find the row that reads correctly.
How the Caesar cipher works
Each letter is replaced by the letter a fixed number of places further along the alphabet, wrapping from Z back to A. With a shift of 3, A becomes D, B becomes E and Z becomes C. To decrypt, shift the same number of places backwards.
The cipher is named after Julius Caesar, who is said to have used a shift of three for private messages.
Why it is not secure
- There are only 25 possible shifts, so every one can be tried in moments.
- Each letter always maps to the same letter, so common letters such as E still stand out.
- It hides text from a casual glance only.
Fun uses
The Caesar cipher is popular for puzzles, escape-room clues, geocaching and teaching the basics of cryptography. ROT13 is used online to hide spoilers.
Limits
Only the 26 English letters are shifted; accented and non-Latin letters are left unchanged. The table of all shifts shows up to the first 300 characters of your text. This is a learning and puzzle tool, not a way to protect sensitive data. Everything runs in your browser and nothing is uploaded.
Why use this caesar cipher and rot13 tool tool
- Any shift from 1 to 25. Set the key with a slider. Decrypting uses the same key in reverse.
- ROT13 in one click. The ROT13 button sets the shift to 13. Because the alphabet has 26 letters, applying it twice gives the original text.
- Brute-force table. See your text decrypted with all 25 shifts at once to find the right one by eye.
- Keeps case and punctuation. Capital letters stay capitals, and numbers, spaces and symbols stay in place unless you choose to keep only letters.
Frequently asked questions
How do I decode a Caesar cipher without the key?
Paste the text and open Show all 25 shifts. Each row shows the text decrypted with a different shift. Scan the rows for the one that reads as normal language. With only 25 possible keys, this takes a few seconds.
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Since 13 is half of 26, the same operation both encrypts and decrypts. It is used to hide spoilers or puzzle answers lightly, not to protect secrets. Many forums and puzzle sites use it this way.
Is the Caesar cipher secure?
No. There are only 25 useful keys, so anyone can try them all quickly, and letter frequencies also give it away. Do not use it to protect passwords or private information. Use modern encryption for real security. Modern tools such as AES, used in password managers and secure messaging, are designed to resist this kind of guessing.
Does it change numbers and punctuation?
No. Only the letters A to Z and a to z are shifted. Numbers, spaces and punctuation stay as they are. You can turn on Keep only letters to remove everything else from the result. This is handy for puzzles where word breaks would give away the answer.
Is my text sent to a server?
No. The shifting is done in your browser as you type, and nothing is uploaded or stored. You canand nothing is uploaded or stored. This also means your messages stay private. You can disconnect from the internet after the page has loaded and it will still work.
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