D2

D2 is a declarative diagram language, and its tool turns plain text into diagrams. The syntax is short and readable, and the output can be styled with themes and a hand-drawn sketch mode.

You write a text file that lists shapes, containers, connections and labels, and D2 lays them out as a diagram. Layout engines such as ELK can be selected, and themes change the overall look. A playground in the browser lets you try the syntax before you install anything, and the examples page shows how common diagrams are written.

• Plain text syntax for shapes and links
• Nested containers for system layouts
• Several themes and a sketch mode
• Layout engine options such as ELK
• Browser playground for testing code

Engineers, architects and technical writers who want diagrams that live in version control next to the code they describe. It also suits teams that prefer writing code to dragging shapes in an editor.

D2 is listed under the MPL-2.0 license, so the tool is free to use under those terms. It runs as a command-line program, and the playground runs in the browser. Diagrams are plain text files, so they diff well in version control, but very large diagrams can be harder to arrange by hand than in a visual editor.