Z85

Z85 is a binary-to-text encoding designed for representing binary data as printable ASCII characters. It was created for the ZeroMQ project to provide a compact, text-safe encoding that can be used in logs, messages, or identifiers where binary data needs to be textual but without introducing problematic characters.

The encoding works by processing data in 4-byte blocks (32 bits). Each block is treated as an unsigned integer and converted to base-85 using a fixed alphabet of 85 printable characters. This means 4 bytes of data are encoded into 5 ASCII characters, making Z85 more compact than hex and often more convenient than Base64 for small blocks. The decoding process reverses this mapping to recover the original bytes. The standard also defines how to handle the final, partial block so that the exact original length can be recovered.

Usage and scope: Z85 is primarily used within the ZeroMQ ecosystem to encode binary payloads for transport and for debugging purposes. It is not a formal IETF standard. Several languages offer implementations (in C and other languages) to integrate Z85 encoding and decoding with ZeroMQ or other text-based workflows.

Advantages and limitations: Z85 provides a space-saving alternative to hex and avoids many control or URL-unsafe characters found in other encodings. However, its adoption is mostly limited to environments that require compatibility with ZeroMQ or similar systems, and it is not as widely standardized or ubiquitous as Base64 or hex.