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

> Easily install the diagram-design skill for Codex in 2 simple steps. Follow our guide to enhance your Codex experience with diagramming capabilities from cathrynlavery/diagram-design.

- Repository: [Cathryn Lavery/diagram-design](https://github.com/cathrynlavery/diagram-design)
- Tags: how-to-guide
- Published: 2026-08-17

---

**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:

```bash
codex plugin marketplace add cathrynlavery/diagram-design

```

This points Codex to the [`.codex-plugin/plugin.json`](https://github.com/cathrynlavery/diagram-design/blob/main/.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:

```bash
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:

```bash
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`](https://github.com/cathrynlavery/diagram-design/blob/main/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`](https://github.com/cathrynlavery/diagram-design/blob/main/type-architecture.md), [`type-flowchart.md`](https://github.com/cathrynlavery/diagram-design/blob/main/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`](https://github.com/cathrynlavery/diagram-design/blob/main/.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:

```bash
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`](https://github.com/cathrynlavery/diagram-design/blob/main/SKILL.md) to parse intent and select the **architecture** diagram type
2. Pulling layout primitives from [`references/type-architecture.md`](https://github.com/cathrynlavery/diagram-design/blob/main/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`](https://github.com/cathrynlavery/diagram-design/blob/main/scripts/verify-plugin-package.py) for CI validation and [`skills/diagram-design/scripts/self_check.py`](https://github.com/cathrynlavery/diagram-design/blob/main/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`](https://github.com/cathrynlavery/diagram-design/blob/main/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`](https://github.com/cathrynlavery/diagram-design/blob/main/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.