PlantUML defines a standardized way to encode diagram text description to a simple string of characters that contains only digits, letters, underscore and minus character. The goal of such an encoding is to facilitate communication of diagrams through URL (see server). This encoding includes compression to keep encoded strings as short as possible.
The encoded metadata is stored in the generated PNG, so the diagram source can be extracted from the diagram itself! (see server).
For example, the following uml text description:
Alice -> Bob: Authentication Request
Bob --> Alice: Authentication Response
is encoded as:
To achieve such an encoding, the text diagram is:
The following diagram:
is compressed to a 428 string length using Deflate
You can use
-decodeurl in the command line flags to encode or decode the text.
You will find here some implementation of this encoder: