pi-loom-mermaid

Show diagrams directly in Pi, with colored boxes, a clearer layout, and connecting lines that are easier to follow.

This extension draws diagrams written in Mermaid, a text format for describing boxes, arrows, and other shapes. It also asks the agent to use diagrams when they explain something more clearly than text.

Install

Requires Pi and Node.js 22.6 or newer.

1. Install the package:

   pi install npm:@yassimba/pi-loom-mermaid
   

2. Set markdown.mermaid to "off" in ~/.pi/agent/settings.json. Merge this into your existing settings; do not replace the file:

   {
     "markdown": {
       "mermaid": "off"
     }
   }
   

   This turns off Pi’s own diagram drawing so this extension can draw instead. If you have another Mermaid extension installed, disable it with pi config.

3. Run /reload in Pi.

Claude Code

The same renderer ships as a Claude Code plugin named loom-mermaid. In Claude Code, run:

/plugin marketplace add Yassimba/loom
/plugin install loom-mermaid@loom

Diagrams then draw in replies on every surface, and the system prompt gains the same note about when to use Mermaid. While a reply streams, a band above the prompt shows the diagram growing; the diagram lands in the transcript when its block closes.

Usage

Ask Pi: “Explain this code with a Mermaid diagram.” Pi draws the diagram in the conversation.

You can also paste the example below. Keep the opening line of three backticks followed by mermaid, and the closing line of three backticks.

To show changes, add :::red after a box for removed code, :::orange for changed code, or :::green for added code. These labels give boxes muted colored borders. Text and backgrounds keep your Pi theme’s colors. The classDef lines in the example set custom border colors.

If a diagram is too wide, Pi shows its code instead. Widen the terminal or ask Pi to split it into smaller diagrams.

Plannotator document export

loom-mermaid-render requires Bun on PATH (also required by Herdr Annotate). The CLI uses Bun because Node cannot strip TypeScript inside installed node_modules; the Pi extension runtime is unchanged. It reads Markdown on stdin and writes pre-rendered diagrams in loom-mermaid fences. Set LOOM_MERMAID_WIDTH to change the default 100-column limit. This format requires the Loom-patched Plannotator TUI: it hides the fences and maps SGR colors, bold, and dim into terminal spans. Hyperlinks are omitted; unsupported or oversized diagrams keep their original Mermaid source. Ordinary Markdown viewers do not understand this colored interchange format.

The same diagram in Pi and GitHub

All three views below use the same Mermaid code.

Pi built-in

Gray boxes. Connecting lines take long paths around the outside.

pi-loom-mermaid

Colored boxes and shorter connecting lines. Small bends mark where lines cross.

GitHub built-in

GitHub draws the code below as a diagram. Copy the code into Pi to compare how it looks.

flowchart TD
    CLI["turbine CLI<br/>shell.main"]:::orange
    LSP["Editor<br/>turbine-lsp"]:::orange
    HTTP["HTTP client"]:::red

    CLI --> SELECT["Select ProjectLayout"]:::orange
    LSP --> WORKSPACE["Discover Projects<br/>EditorWorkspace.open"]:::orange

    SELECT --> RUNTIME["ProjectRuntime.create"]:::orange
    WORKSPACE --> RUNTIME

    ENTRY["Installed turbine.extension<br/>entry points"]:::red --> EXT["Discover, order, and admit<br/>Extensions"]:::orange
    RUNTIME --> EXT
    EXT --> CATALOG["ExtensionCatalog"]:::green
    CATALOG --> FORMATS["InstalledFormats"]:::green
    CATALOG --> LINT["CachedProjectLint"]:::green

    RUNTIME --> SNAPSHOT["ProjectSnapshotCache"]:::green
    RUNTIME --> RUN["CheckRun"]:::green
    RUNTIME --> HISTORY["RunHistoryReader"]:::green

    SNAPSHOT --> COMMANDS["CLI commands"]:::orange
    SNAPSHOT --> SESSION["EditorSession"]:::orange
    SNAPSHOT --> API["Management API"]:::orange

    CLI --> COMMANDS
    LSP --> SESSION
    HTTP --> API

    classDef red stroke:#9f5555
    classDef orange stroke:#9a7438
    classDef green stroke:#4f8560

Update or remove

Update the package, then run /reload:

pi update npm:@yassimba/pi-loom-mermaid

To uninstall:

pi remove npm:@yassimba/pi-loom-mermaid

Delete the "mermaid": "off" setting you added to restore Pi’s own diagram drawing, then run /reload.

Contributing

From the Loom repository root, run npm ci, npm run check, and npm run audit before opening a pull request.

License

MIT. Adapted from pi-lovely-mermaid.