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Caesar Cipher Encoder

Runs in browser

Encode text with a Caesar cipher shift of 1–25. Classic shift-3 Julius Caesar cipher, real-time output, brute-force mode. Nothing uploaded.

Last updated 02 Apr 2026

The Caesar cipher shifts every letter forward by a fixed number of positions. With shift 3, A→D, B→E, Z→C. Non-letter characters pass through unchanged. Choose any shift 1–25, see output in real time, and use Brute Force to test all 25 possibilities at once. Runs entirely in your browser.

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How to use

  1. 1

    Enter your plaintext

    Type or paste the text you want to encode into the left panel. Output updates in real time.

  2. 2

    Set the shift amount

    Use the + and − buttons or type a number between 1 and 25. The default shift of 3 matches the classic Julius Caesar cipher. Shift 13 produces ROT13.

  3. 3

    Copy the encoded ciphertext

    Click Copy next to the output panel to copy the Caesar-encoded text.

  4. 4

    Enable Brute Force to test decodability

    Toggle Brute Force to see all 25 possible shifts for your ciphertext at once — useful for checking how easy it would be to decode.

  5. 5

    Decode later

    Use the Caesar Cipher Decoder with the same shift value to recover the original text, or enable Brute Force to test all 25 options.

Frequently asked questions

What is the Caesar cipher?
The Caesar cipher is a substitution cipher that shifts every letter in the plaintext by a fixed number of positions in the alphabet. It is named after Julius Caesar, who reportedly used shift 3 to communicate with his generals. With shift 3: A→D, B→E, Z→C.
Is this tool safe? Are inputs sent to a server?
No data is uploaded. All encoding runs in your browser. Nothing leaves your device.
How do I decode a Caesar cipher?
Use the Caesar Cipher Decoder with the same shift that was used to encode the message. If you do not know the shift, enable Brute Force mode to see all 25 possibilities and spot the readable one.
What is the difference between Caesar cipher and ROT13?
ROT13 is a special case of the Caesar cipher with shift = 13. Because 13 + 13 = 26 (the full alphabet), ROT13 is self-inverting — encoding and decoding are identical. A general Caesar cipher with any other shift requires the shift value to decode.
Are digits and punctuation affected?
No. The Caesar cipher shifts only the 26 Latin letters (A–Z, a–z). Digits, spaces, and punctuation are passed through unchanged.
Is the Caesar cipher secure for real use?
No. With only 25 possible shifts, any attacker can test all of them in milliseconds. The Caesar cipher is suitable only for educational purposes, puzzles, games, and historical demonstrations — never for protecting sensitive data.
What is brute force mode?
Brute Force mode displays all 25 possible Caesar decodes for the current ciphertext at once. For encoding, it shows how all 25 shifts look — useful for seeing how easily the message could be decoded by a recipient without the key.
What happens when a letter wraps past Z?
Letters wrap around: shifting Z forward by 1 gives A, by 2 gives B, and so on. The modular arithmetic ensures all output characters remain valid letters.
Was Julius Caesar the first to use this cipher?
Caesar is the earliest well-documented user (c. 50 BC), described by Suetonius in 'The Lives of the Twelve Caesars'. Simple letter-shift ciphers likely existed earlier, but the association with Caesar made this the most famous substitution cipher in history.

Encode text with the Caesar cipher — one of the oldest and most famous

encryption techniques in history. Julius Caesar reportedly used a shift of

3 to communicate with his generals around 50 BC.

**How it works:** Each letter in the plaintext is replaced by the letter

that sits a fixed number of positions later in the alphabet. Z wraps around

back to A. Uppercase and lowercase letters are handled independently; all

other characters — digits, punctuation, spaces — pass through unchanged.

**Choosing a shift:** Use any value from 1 to 25. Shift 3 is the classic

Caesar cipher. Shift 13 is ROT13 — a special case where encoding and

decoding are identical because 13 + 13 = 26.

**Brute force mode:** Enable Brute Force to see all 25 possible shifts

for the current input simultaneously — useful for checking how easily

your message could be decoded.

All processing runs in your browser — your text is never uploaded.

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