fasdiagram

fasdiagram is a lightweight open-source diagramming language and rendering engine designed to turn compact textual descriptions into diagrams suitable for documentation and design reviews. The project emphasizes speed, reproducibility, and easy integration into code repositories and build pipelines.

fasdiagram describes diagrams in a plain text format. A description consists of node definitions, edge specifications, and optional attributes for styling and layout. Nodes declare identifiers with labels and shapes; edges connect source and target nodes with optional direction and curvature. Subgraphs or groups enable hierarchical organization.

Rendering is performed by a core engine with backends for vector and raster output. The default backend emits scalable vector graphics (SVG), while other backends can produce PNG or PDF. Layout algorithms include layered and automatic spacing, and themes provide consistent color schemes and typography. Outputs can be standalone files or integrated into other tools through command-line interfaces or library bindings.

Typical use cases include software architecture diagrams, network topologies, state machines, and data flows. The design emphasizes reproducibility: diagrams are derived from text and can be regenerated identically across environments. fasdiagram is intended to fit into common development workflows, with plugin support for editors, documentation generators, and continuous integration systems.

fasdiagram overlaps with other diagram DSLs such as Mermaid, PlantUML, and Graphviz dot, but it emphasizes fast rendering and a minimal, declarative syntax. It is maintained by an open community and released under a permissive license to encourage adoption and contributions.