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Start with imagegen: A Quick Guide to Codex Skills for Everyday Users

Posted May 29, 2026 by XAI Tech Team ‐ 5Β min read

When people first see SKILL.md, it can look like a technical file for developers. For everyday users, a skill is easier to understand as a reusable capability package for Codex.

You do not need to learn the whole plugin system first. Start with a concrete example: imagegen.

imagegen is a built-in Codex system skill for generating and editing images. You can use it for blog covers, product concepts, website hero backgrounds, game assets, UI mockups, or visual variants based on a reference image.

A simple way to remember it:

A prompt explains a task once.
A skill saves a repeatable way of doing a task.

A Minimal Example

Open Codex and type this in the conversation:

Use $imagegen to create a 16:9 blog cover about Codex Skills. Make it clean, technical, and suitable for a documentation site.

This is not a terminal command. You type it in the Codex conversation.

If your Codex environment supports this built-in skill, Codex loads the imagegen SKILL.md and follows its workflow. It understands not only that you want an image, but also how to handle output paths, when to save the result into the current project, and when the image is only a preview.

That is the difference between a skill and a one-off prompt.

What Is SKILL.md?

A skill is usually a folder. The main file is SKILL.md. A simple structure looks like this:

imagegen/
  SKILL.md
  scripts/
  references/
  assets/

SKILL.md tells Codex:

  • what the skill is for
  • when not to use it
  • what workflow to follow
  • whether scripts, references, or assets are involved
  • how to deliver the result

So SKILL.md is not just documentation. It is a working guide that Codex can read.

For imagegen, the skill explains that normal image generation and editing use Codex's built-in image generation path. That path does not require a separate OPENAI_API_KEY. API or CLI fallback only matters when the user explicitly chooses that path.

What imagegen Is Good For

Here are practical examples.

1. Generate a Blog Cover

Use $imagegen to create a cover image for a blog post.
Topic: an AI agent skill library
Ratio: 16:9
Style: clean, modern, suitable for a technical blog
No text and no logo.

2. Create a Website Asset

Use $imagegen to create a background image for a SKILL.md library page in this documentation site.
Requirements: abstract card grid, lightweight technical feel, no text, works for light and dark mode.
If the result is meant for the project, save it to static/images/skills-library-cover.png.

The last sentence matters. If you want the image to become part of the project, tell Codex the target path. Otherwise, the result may remain a preview.

3. Edit an Existing Image

Use $imagegen to make this cover image better for a product documentation site:
reduce decoration, improve information order, and keep the overall color direction.

If you upload images, Codex can treat them as edit targets or references. You can be explicit:

Use the first image as the edit target. Use the second image only as a style reference.

Clear roles produce more predictable results.

system Skills vs curated Skills

On the SKILL page, you will see two main types:

  • .system: built into Codex, usually no installation required
  • .curated: curated by OpenAI, installed when needed

imagegen is a .system skill, so you do not need to install it.

For .curated skills such as chatgpt-apps, linear, pdf, or vercel-deploy, type this inside Codex:

$skill-installer chatgpt-apps

Again, this goes in the Codex conversation, not your system terminal.

Do not run this in a shell:

$skill-installer chatgpt-apps

In a shell, $skill-installer is treated like an environment variable. It is not a command.

After installing a skill, restart Codex so it can pick up the new skill.

How to See Which Skills You Have

In Codex, try:

/skills

You can also type $ and check whether Codex shows an available skill list.

On this site, use the top navigation item 𝑆𝐾𝐼𝐿𝐿 to open the SKILL library. Search by name, use case, or category. For example:

  • image generation: imagegen
  • PDF workflows: pdf
  • website deployment: vercel-deploy or netlify-deploy
  • GitHub CI debugging: gh-fix-ci
  • security review: security-threat-model

You do not need to learn every skill at once.

  1. Start with built-in skills such as $imagegen, $skill-creator, and $skill-installer.
  2. Search for a skill only when you have a clear task.
  3. Install .curated skills with $skill-installer <name>.
  4. Restart Codex after installation.
  5. Invoke the skill by name in your next conversation, such as Use $pdf to check this file.

Codex may also choose a skill automatically based on your request. For beginners, explicit invocation is easier to understand and easier to control.

Common Mistakes

Mistake 1: Treating a Skill Like a Model

A skill is not a model. imagegen is not a model name. It is a workflow.

The model generates or reasons. The skill tells Codex how this class of task should be handled.

Mistake 2: Running $skill-installer in the Terminal

$skill-installer chatgpt-apps belongs in the Codex conversation.

Terminal commands look more like this:

codex

or:

npm i -g @openai/codex@latest

Do not mix the two.

Mistake 3: Installing Every Skill

You do not need to. .system skills are already built in, including:

  • imagegen
  • openai-docs
  • skill-installer
  • skill-creator
  • plugin-creator

Only .curated or third-party skills need installation.

Mistake 4: Trusting Third-Party Skills Blindly

A skill is not always just a prompt. It can include scripts, references, and automation steps. Before installing a third-party skill, review its SKILL.md and scripts.

The One-Sentence Version

If you remember only one thing:

A skill is a reusable Codex workflow. imagegen is the easiest example: type $imagegen in Codex, then describe the image you want in natural language.

To find more skills, start from the 𝑆𝐾𝐼𝐿𝐿 library. For a broader explanation of skills, prompts, and plugins, read What Are OpenAI Skills?.

References: