Caesar Cipher
Encrypt or decrypt text with the classic Caesar shift (13).
- Reading time:
- 2 min
- Last updated:
- Price:
- Free, no signup
Type or paste text to see the result.
What the Caesar Cipher does
The Caesar cipher replaces each letter with one a fixed number of places further down the alphabet. This tool uses a shift of 13, so 'Attack at dawn' becomes 'Nggnpx ng qnja', and pasting that back in reveals the message again.
It's named after Julius Caesar, who, according to Suetonius, used a shift of three to send military notes. It is one of the oldest known ciphers.
Why the Caesar Cipher is useful
The Caesar cipher is where most people first meet cryptography. It shows the core ideas — a plaintext, a rule, a ciphertext — in a way you can check with a pencil.
It also shows why weak ciphers fail: with only 25 possible shifts, anyone can try them all in a minute, which is a great lesson for students.
Also known as: caesar cipher, rot13, text encryption, free caesar cipher, online caesar cipher, caesar cipher online free, caesar cipher tool.
How to use the Caesar Cipher
- 1
Enter a message
Plain English works best since only A–Z letters are shifted.
- 2
Read the shifted text
Each letter has moved 13 places in the alphabet.
- 3
Paste it back to decode
With a shift of 13, the same step reverses the message.
Key features
- Classic letter-shift substitution
- Preserves capital letters
- Leaves spaces, digits and punctuation alone
- Encode and decode in the same box
Benefits
- Hands-on way to teach cipher basics
- Make simple secret notes for games
- Check classroom worksheet answers quickly
Real-life use cases
History lesson
A teacher encodes a short Roman-themed message and asks pupils to crack it by hand, then uses the tool to confirm their answer.
Escape room clue
Someone planning a birthday escape game writes the code for the last lock as a Caesar-shifted word on a card.
Tips for the best results
- To crack an unknown Caesar shift, look for the most common letter — in English it's usually E.
- Short one-letter words in the ciphertext are likely 'a' or 'i'.
- Never rely on it for real secrets; it can be broken without a computer.
Conclusion
Shift a message, share it, and shift it back — the Caesar cipher is a simple, hands-on way to explore how codes work.
Frequently asked questions
What shift does this tool use?
- A shift of 13, which means encoding and decoding are the same action.
Is this the same as ROT13?
- With a shift of 13, yes. Caesar is the general idea; ROT13 is that specific shift.
Did Caesar really use it?
- The Roman historian Suetonius wrote that he used a shift of three for private letters.
How do you break a Caesar cipher?
- Try all 25 shifts or count letter frequencies; both work in minutes.
Does it work on non-English letters?
- No. Only A–Z are shifted, everything else is kept.
Is it safe for passwords?
- No. It's a teaching and puzzle tool, not protection.
Related tools you may need
- ROT13 Encoder — Apply the classic ROT13 letter rotation.
- Letter Frequency Counter — A–Z frequency table for any text.
- HTML Decoder — Decode HTML entities back to plain characters.
- Morse Code Encoder — Convert text into international Morse code.
- HTML Encoder — Escape HTML special characters (< > & " ').
- Morse Code Decoder — Decode Morse code back into readable text.
- Base64 Decoder — Decode Base64 back to readable UTF-8 text.
- HTML Entity Encoder/Decoder — Convert text to HTML entities and back again.
Keep exploring
Browse the full tools directory, filter by category, or read guides on the Text Tools Hub blog.