Raw capture — raw/grok-mermaid.md
url: https://simonwillison.net/2026/Jul/16/grok-mermaid/ title: "Tool: Mermaid to Unicode box art (grok-mermaid)" author: Simon Willison date_fetched: 2026-07-18 date_published: 2026-07-16 site: simonwillison.net tags: [tools, rust, webassembly, mermaid, grok, xai]
grok-mermaid is a new tool that I built that converts Mermaid diagram syntax into terminal-style Unicode box-drawing art, rendered entirely in your browser using WebAssembly.
It supports all of these Mermaid diagram types:
Other diagram types fall back to a framed source listing.
You can adjust the output width, copy out the diagram as text, or click "Copy link to this diagram" for a shareable link.
I learned about the underlying Rust renderer when I was exploring the codebase for the newly open-sourced Grok CLI coding agent. In xai-org/grok-build I found a file called xai-grok-markdown/src/mermaid.rs — a self-contained terminal renderer for Mermaid diagrams, written in Rust.
I figured it would be fun to try that out in a browser via WebAssembly, so I did.
The prompt I ran in Claude Code for web (Fable 5) is shared in this pull request.
A screenshot of the tool shows a Mermaid diagram editor with source code on the left and the rendered flowchart on the right. All of the diagram layout is handled by the Rust code compiled to WebAssembly — there's no JavaScript reimplementation of any layout logic. The example chart illustrates the following flowchart:
Request received → Authenticated? ├─ yes → Rate limit OK? │ ├─ yes → Handle request ─┬─→ Audit log │ └─ no → 429 Too Many Requests │ └─ no → 401 Unauthorized └─→ 200 OK
I compiled the Rust code (unmodified apart from two import lines) into a 163 KB WebAssembly module. There is no JavaScript reimplementation of any layout logic — everything runs the original Rust code via WASM. The build script and source are in the grok-mermaid directory of my tools repository.
The module is a copyright 2023-2026 SpaceXAI and made available under the Apache License 2.0.
Posted 16th July 2026 at 12:33 am