Vigenère Cipher Decoder & Encoder — Free Online Vigenère Solver

Vigenère Cipher Decoder & Encoder — Free Online Vigenère Solver. Free Vigenère cipher decoder and encoder. Encrypt or decrypt text with a keyword, crack a ciphertext without the key, and switch to Beaufort or Autokey — 100% in your browser.

Our Vigenère cipher decoder and encoder turns plain text into polyalphabetic ciphertext — and back — in real time.

Type a keyword, paste your message and the result updates as you type: letters are shifted by the matching key letter, the keyword repeats only over letters, and spaces, digits and punctuation stay in place (or are stripped if you prefer classic block-style ciphertext).

Upper- and lower-case are preserved, accents in the key are ignored, and a live key stream shows exactly which key letter was applied to every character, so this Vigenère encoder doubles as a step-by-step learning aid for students and puzzle solvers.

Lost the keyword?

Switch to decode mode and use the built-in Vigenère solver: it estimates the key length with the index of coincidence, then recovers each key letter with chi-squared frequency analysis — a practical Vigenère cipher decoder without key for English texts of a few sentences or more.

Beyond the standard cipher you can pick the reciprocal Beaufort cipher, the Variant Beaufort, or the Autokey cipher, which extends the key with the plaintext itself.

An interactive Vigenère square (tabula recta) highlights the rows used by your key, making the classic Vigenère table easy to follow by hand. For single-shift ciphers use our Caesar Cipher tool instead.

Everything runs locally in your browser: your messages and keywords are never uploaded to a server, and the Vigenère cipher translator keeps working offline once the page has loaded.

Load the sample to see it in action, swap the result back into the input to check a round trip, copy the output with one click, or share a link that restores your text, key and options.

Remember that Vigenère is a historical cipher — for real security use modern AES in our Encrypt / Decrypt Text tool. Related tools: Morse Code Translator, NATO Alphabet, Letter to Number and Hash Text.

Frequently asked questions

How do I decrypt a Vigenère cipher with a known key?

Select Decode, type the keyword in the Key field and paste the ciphertext into Input text. The plaintext appears in Result, and the Key stream line shows which key letter was applied to each letter. Only the letters A to Z of the key are used; spaces, digits and punctuation in it are ignored.

Can I decode a Vigenère cipher without the key?

Yes, for English text. Select Decode, paste at least 20 letters of ciphertext and click Crack key. The tool estimates the key length (up to 20 letters) with the index of coincidence, finds each key letter by frequency analysis and fills in the key. Longer texts give better results; Crack key does not work with Autokey.

What are the Beaufort, Variant Beaufort and Autokey options?

Beaufort subtracts the plaintext from the key and is reciprocal, so encoding and decoding give the same result. Variant Beaufort shifts in the opposite direction to standard Vigenère. Autokey starts with your keyword and then extends the key with the plaintext itself, so the key never repeats.

What happens to spaces, punctuation and accented letters?

With Keep spaces & punctuation ticked (the default), anything that is not a letter A to Z stays in place and does not use up a key letter; untick it to remove those characters from the result. Upper and lower case are preserved, and accented letters such as é are treated as non-letters.

What is the Vigenère square?

The Vigenère square, or tabula recta, is a 26 by 26 table of shifted alphabets used to encrypt by hand. Click Show square to display it; the rows for the letters in your key are highlighted.

Is the Vigenère cipher secure?

No. It was once called le chiffre indéchiffrable, but it can be broken with frequency analysis, as the Crack key button shows. Use it for puzzles, escape rooms, CTF challenges and learning, not to protect real secrets.

How to use this online tool

Vigenère Cipher Decoder & Encoder — Free Online Vigenère Solver 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

Vigenère Cipher Decoder & Encoder — Free Online Vigenère Solver 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 Vigenère Cipher Decoder & Encoder — Free Online Vigenère Solver 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.