# Vigenère Cipher > Encode and decode the Vigenère cipher with a keyword, or crack a message without the key: the tool finds the key length and the keyword for you. - Page: https://linguaholic.com/tools/vigenere-cipher/ - Type: free online tool (Converters & translators), no sign-up, runs in the browser - Publisher: Linguaholic (https://linguaholic.com/), made by Marcel Iseli - Last updated: October 3, 2026 - Open it pre-filled: https://linguaholic.com/tools/vigenere-cipher/?text=LXFOPV+EF+RNHR&key=LEMON&mode=decode - `text`: text to encode or decode (for example `LXFOPV EF RNHR`) - `mode`: direction: encode (default) or decode (for example `decode`) - `key`: keyword; must contain at least one letter, capped at 64 characters; default KEY (for example `LEMON`) - `open`: open a section: crack (find the key without knowing it), steps (key alignment and Vigenère table rows), frequency (letter counts) or identify (which cipher is this?) (for example `crack`) ## What is the Vigenère cipher? The **Vigenère cipher** encodes a message with a keyword. Each letter of the keyword stands for a Caesar shift (A = 0, B = 1 … Z = 25), and the keyword is repeated along the message so that every letter gets its own shift. Because the shift keeps changing, the same plain letter can turn into different cipher letters, and the simple tricks that break a [Caesar cipher](https://linguaholic.com/tools/caesar-cipher/) stop working. That is why it is called a **polyalphabetic** cipher: it uses several cipher alphabets instead of one. For about three hundred years it had a reputation as unbreakable, and in French it was nicknamed *le chiffre indéchiffrable*, “the indecipherable cipher”. It is not, and the tool above shows how it is broken. The name is said “vee-zhuh-NAIR”, after the French writer Blaise de Vigenère. ## How to use the Vigenère cipher decoder and encoder 1. Choose **Encode** or **Decode**. 2. Type the **keyword**. Only its letters count, so “Lemon”, “LEMON” and “le mon” are the same key. 3. Type or paste the message. The result updates as you type. Spaces, digits and punctuation are copied as they are and do not use up a key letter, which is how most puzzles and textbooks do it. 4. Copy the result, or press **Decode this** to check it decodes back. **Don’t know the key?** Open **Crack it: I don’t know the key**. The tool measures which key length fits the message best, works out each letter of the keyword, and lists the best keys with a preview of each. Press **Use this key**, and if a letter or two is still wrong, correct it in the Keyword box; the decoded text updates as you type. The **Step by step** section lines the keyword up under your message and shows the rows of the Vigenère square it uses, and **Letter frequencies** shows how flat the letter counts of a Vigenère message are. Links can open the tool filled in: `?text=LXFOPV&key=LEMON&mode=decode` decodes straight away, and `&open=crack` opens the cracker. ## Frequently asked questions **What is the Vigenère cipher?** A cipher that uses a keyword to give each letter its own Caesar shift. The keyword repeats along the message, and each key letter (A = 0, B = 1 … Z = 25) says how far to shift the letter it sits under. **How do I decode a Vigenère cipher with the key?** Write the keyword under the code, repeating it and skipping spaces, and shift each letter back by its key letter. In the tool, choose Decode, type the keyword and paste the message. **Can you decode a Vigenère cipher without the key?** Yes, if the message is long enough. Open Crack it in the tool: it finds the key length with the index of coincidence, works out each key letter from letter frequencies and shows the best keys. Plan on about 20 letters of code per key letter. **How do you find the key length of a Vigenère cipher?** Split the code into columns for each possible length and measure how English-like each column's letter counts are (the index of coincidence). At the right length every column is a plain Caesar shift and the score jumps. Repeated letter groups (the Kasiski test) point to the same length. **What is the Vigenère table?** A 26 by 26 square of alphabets, each row shifted one place from the row above, also called the tabula recta. The key letter picks the row, the message letter picks the column, and the cipher letter is where they meet. **How do you pronounce Vigenère?** Roughly vee-zhuh-NAIR, after the sixteenth-century French writer Blaise de Vigenère. **Who invented the Vigenère cipher?** Giovan Battista Bellaso described it in 1553. Blaise de Vigenère published a stronger autokey cipher in 1586, and the repeating-key cipher later became known by his name. **Is the Vigenère cipher secure?** No. It was broken in the nineteenth century and a computer cracks a typical message in a fraction of a second. Only a truly random key as long as the message and never reused, a one-time pad, makes it unbreakable. **Why do spaces and punctuation not change?** The tool shifts letters only and does not use up a key letter on spaces, digits or punctuation, which is the usual convention. Paste a code exactly as you received it so the key stays lined up. ## Data sources The code breaker's English letter frequencies and word checks come from Linguaholic’s English dictionary, built from the open ENABLE and SCOWL word lists. Licenses and notices: https://linguaholic.com/tools/data/dict/v1/NOTICE.txt ## Related tools - [Caesar Cipher](https://linguaholic.com/tools/caesar-cipher/): Encode and decode the Caesar shift cipher with any shift from 1 to 25, or crack a message without the key: every shift is tried and ranked for you. - [Substitution Cipher](https://linguaholic.com/tools/substitution-cipher/): Encode and decode with any cipher alphabet or keyword, or paste a cryptogram and let the solver crack it; then fix any letter yourself. - [Affine Cipher](https://linguaholic.com/tools/affine-cipher/): Encode and decode the affine cipher with keys a and b, see the arithmetic for every letter, or crack a message by trying all 312 keys. - [ROT13](https://linguaholic.com/tools/rot13/): Decode and encode ROT13 instantly (the same step does both), switch to ROT5, ROT18 or ROT47, or try every rotation when it is not ROT13. - [Atbash Cipher](https://linguaholic.com/tools/atbash-cipher/): Encode and decode the Atbash cipher, which swaps each letter with its mirror (A↔Z, B↔Y), with the alphabet chart, step-by-step working and examples. - [Morse Code Translator](https://linguaholic.com/tools/morse-code-translator/): Translate text to Morse code and decode it back, hear it as adjustable-speed sound with a visual flasher, and read the full Morse alphabet, number, and punctuation chart.