Claude Code skills vs Codex skills

Claude Code and OpenAI Codex now both support agent skills and plugin marketplaces, but the install surfaces and bundle manifests are different. The useful comparison starts with the shared core: a skill is still a focused SKILL.md package.

The shared concept

On both platforms, a skill is a directory with a required SKILL.md file, frontmatter such asname anddescription, and optional supporting files such as references, scripts, templates, and assets. The description tells the agent when the skill is relevant. The full instructions are loaded only when needed, which keeps context smaller.

Skills can also travel in plugins. A plugin is the installable bundle: it can package many skills, plus other platform-specific capabilities such as commands, hooks, agents, MCP server configuration, app integration metadata, or visual assets depending on the target platform.

Claude Code today

• Claude Code discovers personal skills from ~/.claude/skills/, project skills from .claude/skills/, and plugin skills bundled under a plugin's skills/ directory.
• Claude Code plugins use .claude-plugin/plugin.json for plugin metadata. Claude marketplaces use .claude-plugin/marketplace.json.
• Users add marketplaces and install plugins inside Claude Code with commands such as /plugin marketplace add and /plugin install. Claude Code can also install configured team plugins from project settings.
• Claude Code skills are model-invoked. Slash commands are separate, user-invoked plugin components, even when a plugin ships both.

Codex today

• Codex skills also use SKILL.md with frontmatter and progressive disclosure. Codex initially sees the skill name, description, and file path, then loads the full instructions when the skill is needed.
• Codex supports optional per-skill metadata in agents/openai.yaml, including interface metadata, invocation policy, and tool dependency declarations.
• Codex plugins use .codex-plugin/plugin.json and can point at bundled skills with "skills": "./skills/". Plugins can also include MCP server configuration and app or connector metadata.
• Codex marketplaces can be added with codex plugin marketplace add from GitHub shorthand, Git URLs, or local directories. Users browse and manage plugins with /plugins.

Key differences at a glance

• Install surface. Claude Code installs named plugins with /plugin install. Codex adds a marketplace source with codex plugin marketplace add, then installs from the /plugins browser.
• Plugin manifest. .claude-plugin/plugin.json for Claude Code, .codex-plugin/plugin.json for Codex.
• Marketplace file. .claude-plugin/marketplace.json for Claude Code, .agents/plugins/marketplace.json for Codex.
• Shared skill core. Both platforms use SKILL.md and model-invoked activation. Platform-specific files refine how the same content is presented, installed, and governed.

How this marketplace serves both

Every skill in Alison's LLM Skills Marketplace keeps the cross-platform core inSKILL.md, references, scripts, and assets. The plugin repositories also publish both.claude-plugin/plugin.json and.codex-plugin/plugin.json, so the same skills can be distributed through both marketplace systems.

This marketplace also keeps compatibility metadata such as agents/openai.yaml for Codex and existing agent metadata used by the Claude-oriented bundles. Treat those as packaging helpers around the shared skill instructions, not as replacements for SKILL.md. Browse the full skill catalog or read what agent skills are if you are new to the concept.

Deciding whether to adopt a marketplace at all? See why use a skills marketplace. Ready to install? Follow the install-from-GitHub guide.

Official documentation

• Claude Code plugins docs: docs.claude.com/en/docs/claude-code/plugins
• Claude Code skills docs: docs.claude.com/en/docs/claude-code/skills
• OpenAI Codex docs: developers.openai.com/codex/plugins
• OpenAI Codex skills docs: developers.openai.com/codex/skills