Keyword-based classical cipher. Enter a key, encode or decode. Letters only are shifted.
A Caesar cipher shifts every letter by the same fixed amount. Vigenere uses a keyword, so each position is shifted by a different amount based on the corresponding key letter, cycling through the keyword. That makes simple frequency analysis much harder.
No. It is a classical cipher, breakable with known techniques (Kasiski examination, frequency analysis on the key length). Use it for puzzles and learning, never for real secrets.
Only letters are enciphered. Spaces, digits and punctuation pass through unchanged, and the original upper/lower case is preserved.