excalidraw-diagram

Excalidraw Diagram Creator

Generate .excalidraw files that argue visually instead of turning prose into labeled boxes.

Sample trigger phrasings: "draw a diagram of this architecture", "visualize this workflow in Excalidraw", "convert this Mermaid flowchart to Excalidraw", "turn this Excalidraw scene into Mermaid".

Setup

If the renderer is not initialized in this environment, run:

uv run scripts/render_excalidraw.py --install-browser

The Excalidraw browser bundle is vendored locally; the renderer serves it from a local HTTP endpoint during export so Chromium loads the packaged module correctly. Refresh it from the repo root with scripts/refresh.sh for the latest upstream JS state from npm.

Theme Selection

1. Read references/theme-catalog.md.
2. If the user does not request a theme, use the catalog default theme: default (dark).
3. Read the selected theme file from references/themes/.
4. Use only colors from that theme. Do not invent hex values.
5. Set both of these in the .excalidraw file:
   • appState.viewBackgroundColor = theme background
   • appState.excalidrawDiagramTheme = selected theme name

Theme implies mode. Do not use a separate dark-mode switch.

Core Principles

• Diagrams should show relationships, causality, and flow that would be weaker in prose.
• Shape should match meaning. If removing the text destroys the idea, redesign the structure.
• Technical diagrams teach with concrete evidence: real event names, payloads, API calls, or UI states.
• Default to free-floating text. Use containers only when they carry meaning or need bindings.
• Mermaid interoperability is semantic, not literal. Preserve graph meaning; don't blindly mimic Mermaid's layout when Excalidraw teaches it better.
• For a quick structural Mermaid derivation from an existing .excalidraw scene, use uv run scripts/excalidraw_to_mermaid.py path/to/file.excalidraw as a starting point, then refine.

Decide The Depth

Use a simple conceptual diagram when:

• Explaining a mental model
• Giving a fast overview
• The audience does not need implementation details

Use a comprehensive technical diagram when:

• Explaining a real system, protocol, or architecture
• The audience needs to learn how parts actually connect
• The diagram should stand on its own as a teaching artifact

For technical diagrams, research the real spec first and include evidence artifacts.

Workflow

1. Understand The System

• Identify the key transformation, decision points, and outputs.
• For technical topics, look up the real data shape, event names, methods, or API surface.
• Decide what the viewer must see, not just what they must read.
• If input or output is Mermaid, read references/mermaid-interoperability.md and choose the Mermaid form that best matches the diagram semantics.

2. Pick A Theme And A Visual Plan

• Choose the theme before generating any colors.
• Choose a different visual pattern for each major concept.
• Prefer lines, clusters, timelines, trees, fan-outs, or comparisons over uniform card grids.
• Use references/design-patterns.md for the pattern library.

3. Plan Multi-Zoom Structure

For comprehensive diagrams, include:

• A summary flow
• Section boundaries
• Detail inside each section

This keeps the diagram readable from afar and useful up close.

4. Build Large Diagrams Section By Section

For larger diagrams:

1. Create the file wrapper and first section.
2. Add one section per edit.
3. Use descriptive IDs.
4. Keep section spacing balanced.
5. Update cross-section bindings when arrows connect across sections.

Do not generate a large technical diagram in one pass.

5. Generate The JSON

Required document shape:

{
  "type": "excalidraw",
  "version": 2,
  "source": "https://excalidraw.com",
  "elements": [],
  "appState": {
    "viewBackgroundColor": "#ffffff",
    "gridSize": 20,
    "excalidrawDiagramTheme": "default"
  },
  "files": {}
}

Rules:

• text and originalText contain only readable text.
• Use fontFamily: 3.
• Prefer roughness: 0 and opacity: 100.
• Every real relationship gets an arrow or structural line.
• In a container, keep bound text under about 70-75% of container width and 60-65% of container height.
• For boxed labels, aim for at least 24px horizontal and 14px vertical padding.
• If a boxed label is too tight, shorten the wording first, then add a line break, then widen the container. Reduce font size only as a last resort.
• Pull element shapes and field structure from references/element-templates.md and references/json-schema.md.

6. Render And Iterate

Render after generating or editing the diagram:

uv run scripts/render_excalidraw.py path/to/file.excalidraw

To render with a non-default theme:

uv run scripts/render_excalidraw.py path/to/file.excalidraw --theme midnight

Then inspect the exported image and fix:

• clipping
• overlap
• ambiguous labels
• boxed labels that feel edge-to-edge
• weak hierarchy
• awkward whitespace
• bad arrow routing
• unreadable evidence artifacts

The renderer emits layout warnings before export when bound text is likely too tight inside a container. Treat warnings as fix-me items, not ignorable noise.

Use references/render-checklist.md for the full loop.

Common Mistakes

• Using generic placeholders for technical systems instead of real formats or event names
• Putting every label inside a box
• Using the same visual structure for every concept
• Skipping theme selection and inventing colors ad hoc
• Forgetting appState.excalidrawDiagramTheme
• Treating render as a final export instead of an iterative design check

Required References

Load each file at the workflow step that calls for it:

• references/theme-catalog.md: theme selection and authoring — load before generating any colors
• references/themes/catalog.json: available themes
• references/design-patterns.md: visual pattern library — load when planning the visual structure
• references/mermaid-interoperability.md: Mermaid to/from Excalidraw prompting workflow — load when the input or output is Mermaid
• references/element-templates.md: Excalidraw element scaffolds — load when generating JSON
• references/json-schema.md: JSON shape notes — load when generating JSON
• references/render-checklist.md: render-view-fix loop — load when iterating on the export

Scripts

• scripts/render_excalidraw.py: render a .excalidraw file to an image; run after every generation or edit (--install-browser on first use)
• scripts/excalidraw_to_mermaid.py: deterministic structural Mermaid export from an existing scene; run when deriving Mermaid from Excalidraw