Free tool · Text Utilities
Caesar Cipher / Simple Encrypt-Decrypt
Encode or decode text using a classic letter-shift cipher.
Shift every letter in your text by a chosen number of positions in the alphabet, the classic Caesar cipher. Enter the same shift value to decode a message back to plain text. This is a historical, educational cipher, not a secure encryption method: it offers no real security and can be broken in seconds.
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How to use Caesar Cipher / Simple Encrypt-Decrypt
Three steps, and nothing to install.
Enter your text
Only letters are shifted; numbers and punctuation pass through unchanged.
Choose a shift value
Use 13 for ROT13, which decodes itself when applied again.
Encode or decode
Decoding uses the same shift value that was used to encode.
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How this works in your browser
Each letter is mapped to its position in the alphabet, shifted by your chosen amount, and wrapped around using modular arithmetic so that shifting past Z returns to A. Case is preserved by handling upper and lower ranges separately, and anything that is not a letter passes through untouched. That modular wrap is the whole cipher, and it is also why it offers no security: with only 25 meaningful shifts, exhaustively trying every one is trivial, and English letter frequencies survive the substitution intact so the shift can usually be identified without even that. Everything runs in your browser.
Who uses Caesar Cipher / Simple Encrypt-Decrypt
Puzzles and escape rooms
Encode a clue that solvers are meant to be able to crack.
Teaching cryptography
Demonstrate keys, algorithms and why key space matters.
Hiding spoilers
Use ROT13 so a punchline is not readable at a glance.
Games and activities
Create simple coded messages for a classroom or party.
Frequently asked questions
What it can and cannot do, and what happens to your files.
Is this secure encryption?
No. The Caesar cipher is a simple historical substitution cipher with no real security, it can be broken almost instantly. Use it for puzzles or learning, not for protecting sensitive information.
How do I decode a message?
Enter the encoded text with the same shift value used to encode it, and select decode to reverse it back to plain text.
Does it work with numbers and punctuation?
Only letters are shifted; numbers, spaces, and punctuation are left unchanged.
How quickly can it really be broken?
Instantly. There are only 25 possible shifts, so trying every one and reading which produces English takes seconds by hand and no time at all by machine. Even without that, letter frequency gives it away: the most common letter in the ciphertext is almost always a shifted E.
What is ROT13?
A Caesar cipher with a shift of 13, which is its own inverse because 13 is half of 26. Applying it twice returns the original. It is used online not for secrecy but to hide spoilers and punchlines from casual reading, which is an honest use of a cipher with no security.
Why is it still worth knowing?
Because it introduces the core ideas cleanly: a key, an algorithm, and the fact that security depends on the key space rather than on the method being secret. It is the standard starting point in cryptography teaching for exactly that reason.
What should I use for actual security?
Established encryption such as AES, through software built for the purpose, alongside a password manager for credentials. Any cipher you can apply by hand offers no meaningful protection against anyone who wants to read the message.
Try the Caesar cipher - free and instant.
Files never leave your device. No upload, no account, and free for unlimited use.