Base91 Encoder and Decoder [2025]

Base91 is a binary-to-text encoding scheme that is more efficient than Base64. It uses 91 printable ASCII characters to represent binary data, achieving better compression than Base64 while remaining readable and safe for text protocols.

The encoding uses ASCII characters from 33 ('!') to 126 ('~'), excluding quotes and backslash for better compatibility. This wider character set allows Base91 to encode more bits per character than Base64, resulting in shorter encoded strings.

Encoding Process

Base91 processes input in chunks, using a variable bit-length encoding scheme to maximize efficiency. The algorithm maps 13 or 14 bits of input into two Base91 characters, achieving better compression than Base64's fixed 6-bit encoding.

Character Set:

The encoding uses 91 printable ASCII characters:

• • A-Z, a-z (52 characters)
• • 0-9 (10 characters)
• • 29 special characters: !#$%&()*+,./:;<=><=>?@[]^_`{|}~"