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Vigenere Cipher

Encode and decode Vigenere cipher text with a keyword, preserving case and punctuation, and watch the running key line up with each letter.

Direction

Using 5 key letters. The keyword repeats across the text and skips anything that is not a letter.

Everything runs in your browser. Nothing is uploaded.

Key alignment

Each letter of your text with the keyword letter that shifts it beneath. The keyword repeats across letters and skips spaces, digits, and punctuation.

HL
eE
lM
lO
oN
, 
· 
WL
oE
rM
lO
dN
! 

How to decode a Vigenere cipher online

  1. Enter your text

    Type or paste the message you want to encode or decode into the text box.

  2. Choose a keyword

    Enter the secret keyword, which repeats across the letters to control how far each one shifts.

  3. Copy the result

    Read the encoded or decoded output and copy it with one tap, or check the key alignment to see how each letter moved.

Why use this tool

Encode and decode

Scramble a message with your keyword, then switch direction to turn coded text back into plain language.

Keyword sets the shift

Each letter of your keyword decides how far the matching letter of the text moves, repeating across the message for a stronger scramble than a single fixed shift.

Case and punctuation preserved

Uppercase and lowercase letters keep their case while spaces, digits, and punctuation pass through untouched.

See the key alignment

A live panel lines your keyword up beneath each letter, so you can watch the running key skip over spaces and symbols and land only on letters.

Runs entirely in your browser

Everything happens on your device with no upload, no account, and no usage limit.

About this tool

The Vigenere cipher hides a message by shifting each letter using a repeating keyword instead of one fixed amount. The first letter of the keyword shifts the first letter of your text, the second keyword letter shifts the second, and so on, wrapping back to the start of the keyword once you run out. Because the shift changes from letter to letter, the same plaintext letter can map to different coded letters, which is what makes it much harder to break than a simple shift cipher.

This tool encodes and decodes Vigenere text as you type. It keeps upper and lower case intact and passes spaces, digits, and punctuation straight through, advancing the keyword only over the letters it actually encrypts. A key alignment panel shows the running keyword lined up beneath each letter, so you can see exactly how the shift is chosen and why non-letters are skipped. Pick a memorable keyword, share it privately with whoever needs to read the message, and keep it out of the text itself.

Reach for it when you are solving a puzzle, building a capture-the-flag challenge, or learning how classical ciphers work. If you only need a single fixed shift, the Caesar cipher is simpler, and ROT13 is the common half-alphabet version. For another everyday text transform, try the Base64 encoder. Like all classical ciphers, the Vigenere offers no real security against modern analysis, so never use it to protect anything sensitive.

Frequently asked questions

How does a Vigenere cipher work?
Each letter is shifted by an amount taken from a repeating keyword. Line the keyword up under your text, letter by letter, and every text letter moves forward by the position of the keyword letter above it, where A means no shift, B means one, C means two, and so on. When the keyword runs out it starts over from the beginning.
How do I decode a Vigenere cipher?
Switch the direction to Decode and enter the same keyword that was used to encode the message. The tool shifts every letter back by the matching keyword amount, so the original text appears in the result as you type.
What makes a good keyword?
Longer keywords with a mix of different letters scramble the text more thoroughly, because the shift pattern takes longer to repeat. Only letters in the keyword are used; any spaces, digits, or symbols you type in it are ignored, and case does not matter.
Does it keep capital letters and punctuation?
Yes. Uppercase letters stay uppercase and lowercase stay lowercase, and everything that is not a letter, including spaces, numbers, line breaks, and punctuation, passes through exactly as you typed it while the keyword advances only over the letters.
Is my text uploaded anywhere?
No. Everything runs in your browser; nothing is sent to a server, stored, or logged.
Is the Vigenere cipher secure?
No. It resisted casual code breakers for centuries but is straightforward to break with modern analysis, especially once the keyword length is guessed. Treat it as a puzzle or a learning tool, never as a way to protect real secrets.

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