How does the Vigenère cipher work?

Each letter of the message is shifted by the corresponding letter of a repeating keyword: A shifts by 0, B by 1, and so on. This makes it a polyalphabetic cipher that is much harder to break than a single Caesar shift.

What happens to spaces and numbers?

Only letters A–Z are enciphered. Digits, spaces and punctuation pass through unchanged, and any non-letter characters you type in the keyword are ignored.

Is my text uploaded anywhere?

No. The cipher runs entirely in your browser — nothing is sent to a server.

Vigenère Cipher Encoder & Decoder

Encrypt and decrypt text with a keyword-based Vigenère cipher.

Vigenère cipher encoder and decoder

The Vigenère cipher uses a repeating keyword to shift each letter of your message by a different amount, making it far stronger than a plain Caesar shift. Choose encrypt or decrypt, enter a keyword, and type your text — the result updates instantly.

Everything happens in your browser, so your message and keyword never leave your device.