Vigenère Automatic Solver

Try to recover the unknown Vigenère keyword from ciphertext. The solver compares English letter frequencies across likely key lengths, tests candidate keys and ranks readable plaintext. For best results, use at least 100–150 letters.

Results are guesses, not guaranteed answers. Short text, proper names, numbers encoded as words, and non-English messages can confuse statistical analysis. Try different key lengths and examine several candidates.

Test or adjust a keyword

The existing Vigenère Cipher is still available for standard encryption and decryption.

How the automatic solver works

The cipher uses a repeating keyword to shift letters. This tool estimates promising lengths using index of coincidence and repeated-pattern evidence, compares letter frequencies for each key position, then evaluates candidate plaintext for English letter and word patterns. It preserves non-letter characters but they do not advance the key.

This solver is designed for standard Vigenère, not Beaufort, autokey, running-key or one-time-pad ciphers. No text is uploaded to a server.