Plugin Creator Skill for Codex

Plugin Creator

Quick Start

• Run the scaffold script:

  # Plugin names are normalized to lower-case hyphen-case and must be <= 64 chars.
  # The generated folder and plugin.json name are always the same.
# Run from repo root (or replace .agents/... with the absolute path to this SKILL).
# By default creates in ~/plugins/<plugin-name>.
python3 .agents/skills/plugin-creator/scripts/create_basic_plugin.py <plugin-name>

• Open <plugin-path>/.codex-plugin/plugin.json and replace [TODO: ...] placeholders.

• Generate or update the personal marketplace entry when the plugin should appear in Codex UI ordering:

# Personal marketplace entries default to ~/.agents/plugins/marketplace.json.
python3 .agents/skills/plugin-creator/scripts/create_basic_plugin.py my-plugin --with-marketplace

If the current Git repo already has .agents/plugins/marketplace.json and the user has not said

whether the plugin is personal or shared with their team, ask before generating a marketplace entry.

When they choose the repo marketplace, use:

python3 .agents/skills/plugin-creator/scripts/create_basic_plugin.py my-plugin \
  --path ./plugins \
  --marketplace-path ./.agents/plugins/marketplace.json \
  --with-marketplace

• Generate/adjust optional companion folders as needed:

python3 .agents/skills/plugin-creator/scripts/create_basic_plugin.py my-plugin \
  --path <parent-plugin-directory> \
  --marketplace-path <marketplace-json-path> \
  --with-skills --with-hooks --with-scripts --with-assets --with-mcp --with-apps --with-marketplace

<parent-plugin-directory> is the directory where the plugin folder <plugin-name> will be created (for example ~/code/plugins).

What this skill creates

• Default marketplace-backed scaffolds are personal: ~/plugins/<plugin-name>/ plus

~/.agents/plugins/marketplace.json.

• If the current Git repo already has .agents/plugins/marketplace.json and the user has not said

personal vs team, ask which marketplace to update before generating a marketplace entry.

• Creates plugin root at /<parent-plugin-directory>/<plugin-name>/.
• Always creates /<parent-plugin-directory>/<plugin-name>/.codex-plugin/plugin.json.
• Fills the manifest with the full schema shape, placeholder values, and the complete interface section.
• Creates or updates the selected marketplace when --with-marketplace is set.
• If the marketplace file does not exist yet, seed top-level name plus interface.displayName placeholders before adding the first plugin entry.
• <plugin-name> is normalized using skill-creator naming rules:
• My Plugin → my-plugin
• My--Plugin → my-plugin
• underscores, spaces, and punctuation are converted to -
• result is lower-case hyphen-delimited with consecutive hyphens collapsed
• Supports optional creation of:
• skills/
• hooks/
• scripts/
• assets/
• .mcp.json
• .app.json

Marketplace workflow

• Personal plugins use ~/.agents/plugins/marketplace.json.
• Repo/team plugins use <repo-root>/.agents/plugins/marketplace.json.
• Marketplace root metadata supports top-level name plus optional interface.displayName.
• Treat plugin order in plugins[] as render order in Codex. Append new entries unless a user explicitly asks to reorder the list.
• displayName belongs inside the marketplace interface object, not individual plugins[] entries.
• Each generated marketplace entry must include all of:
• policy.installation
• policy.authentication
• category
• Default new entries to:
• policy.installation: "AVAILABLE"
• policy.authentication: "ON_INSTALL"
• Override defaults only when the user explicitly specifies another allowed value.
• Allowed policy.installation values:
• NOT_AVAILABLE
• AVAILABLE
• INSTALLED_BY_DEFAULT
• Allowed policy.authentication values:
• ON_INSTALL
• ON_USE
• Treat policy.products as an override. Omit it unless the user explicitly requests product gating.
• The generated plugin entry shape is:

{
  "name": "plugin-name",
  "source": {
    "source": "local",
    "path": "./plugins/plugin-name"
  },
  "policy": {
    "installation": "AVAILABLE",
    "authentication": "ON_INSTALL"
  },
  "category": "Productivity"
}

• Use --force only when intentionally replacing an existing marketplace entry for the same plugin name.
• If the selected marketplace file does not exist yet, create it with top-level "name", an "interface" object containing "displayName", and a plugins array, then add the new entry.

• For a brand-new marketplace file, the root object should look like:

{
  "name": "[TODO: marketplace-name]",
  "interface": {
    "displayName": "[TODO: Marketplace Display Name]"
  },
  "plugins": [
    {
      "name": "plugin-name",
      "source": {
        "source": "local",
        "path": "./plugins/plugin-name"
      },
      "policy": {
        "installation": "AVAILABLE",
        "authentication": "ON_INSTALL"
      },
      "category": "Productivity"
    }
  ]
}

Required behavior

• Outer folder name and plugin.json "name" are always the same normalized plugin name.
• Do not remove required structure; keep .codex-plugin/plugin.json present.
• Keep manifest values as placeholders until a human or follow-up step explicitly fills them.
• If creating files inside an existing plugin path, use --force only when overwrite is intentional.
• Preserve any existing marketplace interface.displayName.
• When generating marketplace entries, always write policy.installation, policy.authentication, and category even if their values are defaults.
• Add policy.products only when the user explicitly asks for that override.
• Keep marketplace source.path relative to the selected marketplace root as ./plugins/<plugin-name>.
• When the workflow created or updated a marketplace-backed plugin, end the final user-facing

response with a short Codex app handoff. Say To view this in the Codex app: and write

View <normalized plugin name> and Share <normalized plugin name> as Markdown links, not raw

URLs or code spans.

• The View deeplink uses codex://plugins/<normalized plugin name>?marketplacePath=<absolute marketplace.json path>.

The Share deeplink uses the same URL with &mode=share.

• Replace the placeholders with the real normalized plugin name and absolute marketplace.json

path from the scaffolded plugin. URL-encode the path segment and query value when needed.

• Do not add pluginName or hostId query parameters to these deeplinks. Codex derives both after

the user clicks the link.

• Do not emit the View <normalized plugin name> or Share <normalized plugin name> links when no marketplace entry was

created or updated.

Reference to exact spec sample

For the exact canonical sample JSON for both plugin manifests and marketplace entries, use:

• references/plugin-json-spec.md

Validation

After editing SKILL.md, run:

python3 <path-to-skill-creator>/scripts/quick_validate.py .agents/skills/plugin-creator