Mermaid diagrams now fit back into the terminal

Simon Willison highlighted mermaid-ascii, a Go library compiled to WebAssembly that converts Mermaid diagrams into ASCII and Unicode box drawing art directly in the browser. The tool description says it supports flowcharts with labeled edges, subgraphs, colors, sequence diagrams, notes and control flow fragments.

Diagrams move back into places where images get in the way

Willison found the older AlexanderGrooff/mermaid-ascii library after building his own Mermaid to ASCII tool on top of Rust code from Grok Build. He compiled this version to WebAssembly as well so he could compare the two implementations.

The important part is not the conversion trick by itself. It is that the output can live where PNG or SVG feels awkward: README diffs, terminal tools, changelogs, issue comments and plain text documentation.

For developers, a readable diff beats a pretty render

Mermaid became a convenient syntax for quick diagrams, but its weakness shows up when a team wants to review a change as text. ASCII output does not pretend to be visually perfect. It gives teams a cheaper control layer for places where the change matters more than the exported image.

That matters for AI tooling too. Agents can generate Mermaid easily, but validating the diagram is often harder than producing it. A text render gives both humans and automated checks an artifact that can sit inside review without opening another tool.

WebAssembly does not make it a universal diagram platform

The source is a short curator post, not a benchmark. It does not tell us how the library handles very large diagrams, edge cases in Mermaid syntax or long term maintenance. Willison frames it as a comparison tool, not as a replacement for a full renderer.

The real limit is readability. Once a diagram grows, an ASCII map can turn into a carpet of characters. The practical value sits with smaller structures, not wall sized architecture posters.

Adoption will be decided by boring review workflows

The signal to watch is whether mermaid-ascii remains a neat demo or shows up in CLI tools, documentation generators and GitHub review workflows. That would prove text rendering is not nostalgia, but an operational format.

The second question is whether the same pattern spreads to other visual formats. AI tools now produce more diagrams than ever. Without cheap review surfaces, teams will keep generating images that nobody fully trusts during review.

Lilith's verdict

The best diagram is sometimes not the one that shines in a slide deck. It is the one that survives a code review queue, read in a terminal while someone holds coffee in one hand.