How to Install the Diagram‑Design Skill for Codex in 2 Steps

TL;DR: Run codex plugin marketplace add cathrynlavery/diagram-design then codex plugin add diagram-design@diagram-design to install the diagram‑design skill for Codex.

The diagram‑design skill, developed by Cathryn Lavery, turns natural language prompts into production‑ready architecture diagrams, flowcharts, and 25 other visual types. Installing this Codex plugin takes under a minute and unlocks AI‑powered diagram generation directly in your Coding Agent workflows.

Prerequisites for Installing Diagram‑Design for Codex

Before you begin, confirm you have:

• The Codex CLI installed and authenticated on your local machine
• Terminal access with codex in your system PATH
• GitHub repository access to cathrynlavery/diagram-design

Step 1: Add the Repository to Codex's Marketplace

Register the plugin source so Codex knows where to fetch the package. This command only needs to run once per Codex installation:

codex plugin marketplace add cathrynlavery/diagram-design

This points Codex to the .codex-plugin/plugin.json manifest, which registers the skill's metadata, versioning, and entry points.

Step 2: Install the Diagram‑Design Plugin

Pull the skill into your active Codex environment:

codex plugin add diagram-design@diagram-design

Codex downloads the package, validates it against the manifest, and registers the skill's commands and prompts.

Verify and Update the Installation

Codex refreshes its plugin list automatically at startup. To force an immediate update without restarting:

codex plugin marketplace upgrade diagram-design

Then launch a new Codex session or run codex reload if your runtime supports hot‑reloading.

What Gets Installed: Key Files and Structure

Understanding the installed components helps you debug and extend the skill:

Path	Purpose
skills/diagram-design/SKILL.md	Core behavior definition, type selection logic, and design system configuration
skills/diagram-design/references/	Per‑diagram type specifications (e.g., type-architecture.md, type-flowchart.md)
skills/diagram-design/assets/	HTML templates, SVG icons, and example diagrams for offline rendering
commands/	Slash‑command implementations: export-diagram, import-mermaid, profile
prompts/	Natural‑language prompt templates for diagram generation
.codex-plugin/plugin.json	Marketplace manifest that Codex parses during installation

The skill is self‑contained: generated diagrams produce standalone .html files with no external CDN dependencies.

Using the Diagram‑Design Skill After Installation

Once installed, invoke the skill through natural language in any Codex chat:

codex

> Create an architecture diagram showing my microservices: API gateway, three Node.js services, PostgreSQL primary‑replica, and Redisson cache layer.

Codex executes this by:

1. Loading SKILL.md to parse intent and select the architecture diagram type
2. Pulling layout primitives from references/type-architecture.md
3. Rendering a self‑contained HTML file with light, dark, or full‑editorial theme variants
4. Returning the file path for local preview

Keeping the Skill Updated

Because diagram‑design is packaged as a marketplace plugin, updates arrive automatically:

• Automatic: Codex refreshes marketplace cache on restart
• Manual: Run codex plugin marketplace upgrade diagram-design to pull the latest version immediately

The repository includes scripts/verify-plugin-package.py for CI validation and skills/diagram-design/scripts/self_check.py for runtime quality checks.

Summary

• Install once per environment: codex plugin marketplace add cathrynlavery/diagram-design followed by codex plugin add diagram-design@diagram-design
• Force updates: codex plugin marketplace upgrade diagram-design
• Core configuration: Lives in skills/diagram-design/SKILL.md with type references in skills/diagram-design/references/
• Output format: Standalone HTML files with embedded assets—no network required to view
• Update mechanism: Automatic via marketplace refresh or manual CLI upgrade

Frequently Asked Questions

Does the diagram‑design skill work offline after installation?

Yes. Once installed, all templates, icons, and rendering logic are local to your Codex environment. Generated diagrams produce standalone HTML files with no external dependencies.

What diagram types does the skill support?

The skill supports 27 diagram variants including architecture diagrams, flowcharts, sequence diagrams, ER diagrams, Gantt charts, and C4 models. Reference files for each type live in skills/diagram-design/references/.

How do I uninstall the diagram‑design skill?

Run codex plugin remove diagram-design to uninstall. The marketplace registration remains unless you explicitly run codex plugin marketplace remove cathrynlavery/diagram-design.

Can I customize the default styling for all generated diagrams?

Yes. Edit skills/diagram-design/SKILL.md to modify the design system defaults, or create custom type references in the references/ directory. Changes take effect on the next Codex session.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}