/common-architecture-diagramming

name: common-architecture-diagramming
description: Draw architecture diagrams as editable draw.io files with a fixed house style, C4 levels, and evidence-tagged shapes. Use when producing a system context, container, deployment, data flow, sequence, or state diagram, or redrawing an ASCII or Mermaid one.
metadata:
  triggers:
    files:
      - "ARCHITECTURE.md"
      - "**/*.drawio"
      - "**/*.mermaid"
      - "docs/architecture/**"
    keywords:
      - diagram
      - c4
      - drawio
      - mermaid
      - erd
      - entity relationship
      - schema diagram
      - aws
      - architecture diagram
      - solution architecture
      - system context
      - deployment diagram

Architecture Diagramming Standard

**Priority: P1 (HIGH)**

Pipeline

Never hand-write mxGraph XML. Write a spec; the scripts own every visual decision, so diagrams stay identical across authors, repositories, and sessions.

1. Write `spec.json` — schema in [diagram-spec.md](references/diagram-spec.md). For an ERD, generate it: `python3 scripts/schema_to_spec.py db/schema.sql --title "<System> — ERD" -o spec.json` 2. `python3 scripts/validate_spec.py spec.json` 3. `python3 scripts/render_drawio.py spec.json -o docs/architecture/<slug>.drawio --strict` (exit 2 = a layout finding; change the spec, per [layout-rules.md](references/layout-rules.md)) 4. Export the image: a draw.io MCP tool if the session has one, else `python3 scripts/export_drawio.py docs/architecture/<slug>.drawio -f png -o docs/architecture/<slug>.png`, else ship the `.drawio` and say the image was not exported. See [export paths](references/mermaid-fallback.md).

Commit the `.drawio` as the source of truth; the image is a copy for a deck.

Guidelines

• **Name the audience and the decision** before drawing anything.
• **One C4 level per diagram**: context, container, or component, never mixed.
• **Pick the type from the message**, not from habit. See [diagram-selection.md](references/diagram-selection.md).
• **Evidence per node** as `path:line`. A node with no evidence renders dashed and

marked UNVERIFIED — leave the flag showing rather than asserting a guess.

• **Put the number on the box.** `metric` carries the load or SLO that sized the node,

`constraint` says why it exists; never invent either.

• **Label every edge** with its protocol or event; use `style: async` for events.
• **Cloud icons only where verified.** `gcp:*` and `aws:*` are official icons; every other

vendor is a `cloud:*` kind with the service named in `sublabel`. No Azure logos exist in the bundle, so Azure is always `cloud:*`.

• **Exec audience caps at 12 nodes.** Past that, split by level or by flow.
• **Legend and title block are generated.** Do not remove or duplicate them.
• **Refine in draw.io, not in XML.** Re-running the renderer overwrites layout tweaks.

Anti-Patterns

• **No hand-written XML**: Write the spec, run the renderer.
• **No invented boxes**: Omit what the evidence does not support.
• **No mixed levels**: Table columns never appear in a context diagram.
• **No unlabeled arrows**: State the protocol or the event.
• **No mystery acronyms**: Expand every abbreviation on first use.
• **No orphan nodes**: Connect it or cut it.

Red Flags

| Thought | Reality | |---------|---------| | "It is one box, I will write the XML" | The renderer owns style, legend, and title block. Use it. | | "Close enough, I will guess this service" | Guesses ship as facts. Omit the evidence and let it render UNVERIFIED. | | "Managers want the whole system on one page" | Past 12 nodes they stop reading. Split it. |

References

• [Diagram spec](references/diagram-spec.md) · [Style catalog](references/style-catalog.md) · [House style](references/house-style.md)
• [Source extraction](references/source-extraction.md) · [Exec readability](references/exec-readability.md)
• [C4 model](references/c4-model.md) · [Cloud](references/cloud-architecture.md) · [Best practices](references/best-practices.md)
• [Layout rules](references/layout-rules.md) · [Checklist](references/checklist.md) · [Export paths and Mermaid fallback](references/mermaid-fallback.md)
• Runnable examples: `assets/fixtures/<type>.spec.json`, one per diagram type, plus schema samples under `assets/fixtures/schemas/`.
• Batch or delegated drawing: `specialist-solution-diagrammer`.