What is a Caesar cipher?

A Caesar cipher is a substitution cipher that shifts every letter in a message by a fixed number of positions along the alphabet. For example, with a shift of 3, A becomes D, B becomes E, and Z wraps around to C. It is named after Julius Caesar, who used a shift of 3 for military communications around 58 BC.

How do I decode a Caesar cipher if I don't know the shift?

Click "Show all 25 shifts" to reveal every possible decoded version of your text simultaneously, ranked by English-language likelihood. The shift that produces the most plausible English text is highlighted with a star and ranked first. Click the row to apply that shift.

Is ROT13 a Caesar cipher?

Yes — ROT13 is a Caesar cipher with a fixed shift of 13. Because the English alphabet has 26 letters, shift 13 is self-inverse: applying it twice returns the original text. Setting the shift slider to 13 on this tool produces the same result as a ROT13 encoder.

Does the Caesar cipher work on numbers and punctuation?

No — the Caesar cipher only shifts letters (A–Z and a–z). Numbers, spaces, punctuation, and other characters pass through unchanged. Case is always preserved.

How secure is the Caesar cipher?

The Caesar cipher is not secure for protecting sensitive information. There are only 25 possible shifts, so an attacker can try all of them in seconds — or use letter frequency analysis to identify the shift from the most common letters in the ciphertext.

Workspace

Input text

Processed locally.

Mode

Shift

113 = ROT1325

Output (shift 3, decode)

Output appears here as you type…

Letters to Numbers

Trusted Conversion Tools

Caesar Cipher Decoder & Encoder

Our free Caesar Cipher Decoder lets you encode or decode any Caesar-shifted text with a shift slider from 1 to 25 — and includes a brute-force mode that shows all 25 possible decoded outputs simultaneously, ranked by English-language likelihood so you can crack any Caesar cipher even without knowing the shift.

Who Is It For?

Puzzle & Escape Room Enthusiasts

Cracking Caesar-shifted clues, hints, and answers without knowing the shift in advance — just paste the ciphertext and use brute-force mode.

CTF Competitors

Quickly testing all 25 Caesar shifts against captured ciphertext during Capture the Flag cryptography challenges.

Students & Cryptography Learners

Learning how Caesar ciphers work by encoding and decoding messages, exploring all 25 shift possibilities, and seeing how English-likelihood scoring identifies plaintext.

Teachers & Educators

Creating and grading Caesar cipher exercises by encoding messages with a chosen shift and decoding submitted answers.

Writers & Game Designers

Encoding secret messages, puzzle answers, or in-game lore with any shift value and verifying the ciphertext is correctly reversible.

How It Works

Type or paste ciphertext into the input box. Use the shift slider (1–25) or +/− buttons to set the shift value, then select Decode to reverse the shift or Encode to apply it. The output updates instantly. If you do not know the shift, click "Show all 25 shifts" to reveal every possible decoded version simultaneously, each scored by English-language likelihood. The most probable shift is marked with a star — click it to apply.

Features

Shift slider from 1 to 25 with keyboard-accessible +/− buttons
Encode and Decode modes — switch without clearing text
"13 = ROT13" label on the slider highlights the self-inverse shift
Best-guess chip auto-detects the most likely shift for unknown ciphers
Brute-force panel shows all 25 shifts ranked by English-likelihood score
Click any brute-force row to instantly apply that shift
Copy to clipboard and clear buttons
100% browser-based — your text never leaves your device

Other Tools

Explore more tools by clicking the + button above

Letters to Numbers Converter

Convert letters to numbers using A1Z26 cipher

A1Z26 Translator

Translate letters to numbers with the A1Z26 alphabet

A1Z26 Decoder and Encoder

Encode letters to A1Z26 numbers and decode numbers back to letters instantly

A0Z25 Cipher Translator

Convert text using A0Z25 cipher encoding

A0Z25 Decoder

Decode A0Z25 encoded numbers back to letters instantly

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