Caesar Cipher Decoder & Encoder — Free Shift Cipher & ROT13 Translator

Caesar Cipher Decoder & Encoder — Free Shift Cipher & ROT13 Translator. Free Caesar cipher decoder and encoder. Encrypt or decrypt with any shift, detect the key automatically with the built-in solver, brute-force all 26 shifts, and use ROT13 or ROT47.

Runs in your browser. Encrypt or decode messages with our free Caesar cipher decoder and encoder. Type your text, pick a shift from 0 to 25 and the result updates as you type.

This shift cipher replaces each letter with the one a fixed number of places further down the alphabet, which is why it is also called a Caesar shift or Caesar code.

The substitution alphabet under the output works like a Caesar cipher wheel: it shows which plain letter becomes which cipher letter for the current key.

Capital and lowercase letters are kept, and you can choose to shift digits, strip spaces and punctuation, or force the output to upper or lower case. Don't know the key?

The built-in Caesar cipher solver tries every key and scores each result against English letter frequencies (a chi-squared test). It then highlights the most likely plaintext, so you can decode it in one click.

You can also open the full brute force table of all 26 shifts and copy or apply any row. For the classic special cases, switch to ROT13, a shift of 13 where encoding and decoding are the same, which makes this a quick ROT13 decoder.

Or switch to ROT47, which also rotates digits and symbols across printable ASCII. Teachers, students, escape-room designers and CTF players use this Caesar cipher translator to explain substitution ciphers, check homework and solve puzzles.

Load the sample ciphertext to see the solver at work, swap the output back into the input to reverse a step, or share a link that restores your text and settings. Everything runs in your browser, so your messages are never uploaded.

For a stronger polyalphabetic cipher with a keyword, try our Vigenère Cipher. Related tools: Morse Code Translator, Text to Binary, Base64 Encoder and Hash Text.

Frequently asked questions

How do I decode a Caesar cipher without knowing the key?

Paste the ciphertext into Input text. Once it has at least 15 letters, the solver card shows the Most likely key, found by scoring all 26 shifts against English letter frequencies; click Decode with this key to apply it. Turn on Brute Force to see all 26 results and pick one with Use.

How do I encrypt text with a Caesar shift?

Choose Encode and Caesar, set the Shift with the slider or number box (0 to 25), and type your text. Each letter moves that many places along the alphabet, so with shift 3 A becomes D, and the Result updates as you type. The substitution alphabet table shows the full letter mapping for the key.

What is the difference between Caesar, ROT13 and ROT47?

Caesar lets you choose any shift from 0 to 25 for letters. ROT13 is a fixed shift of 13, so encoding and decoding are the same operation. ROT47 rotates all 94 printable ASCII characters, including digits and punctuation, by 47 and is also its own inverse.

Are numbers, spaces and punctuation changed?

Only the letters A to Z are shifted, and upper or lower case is kept. Tick Shift numbers (0-9) to rotate digits as well. Untick Keep spaces & punctuation to remove everything else from the output, and use Output case to force upper or lower case.

Can I share my message and settings?

Yes. Copy link creates a URL containing your text and settings, so anyone who opens it sees the same result. Because the text is placed in the link, avoid sharing links to sensitive messages. Apart from that, everything runs in your browser and nothing is uploaded.

Is the Caesar cipher secure?

No. With only 25 useful keys it can be broken in seconds, as the built-in solver shows. Use it for puzzles, teaching and CTF challenges, not to protect real secrets.

How to use this online tool

Caesar Cipher Decoder & Encoder — Free Shift Cipher & ROT13 Translator is designed for fast browser workflows when you need to format, validate, convert, decode, encode, generate, or inspect data without opening a heavy desktop app. Start with the input field or visible options, review the result, then copy or download the output for the next step.

Private processing in your browser

Caesar Cipher Decoder & Encoder — Free Shift Cipher & ROT13 Translator keeps the normal processing step local in your browser. That is useful for code snippets, tokens, documents, configuration values, text samples, and other material that should not be sent to a remote service unless you explicitly choose to share it.

When this tool is useful

Use Caesar Cipher Decoder & Encoder — Free Shift Cipher & ROT13 Translator for repeatable developer tasks, technical documentation, QA checks, quick conversions, debugging, content cleanup, and internal team workflows. The page focuses on clear inputs, immediate feedback, and output that is easy to reuse in code, reports, tickets, emails, or notes.

Practical tips

Before copying the final result, check important details such as spacing, casing, filenames, encoding, token structure, line breaks, or output format. Small checks prevent mistakes when the result is reused in source code, API requests, documentation, spreadsheets, or shared files.