Compare
Claude API vs Codex CLI
Side-by-side comparison of Claude API and Codex CLI for SKILL.md agent skills — install model, shell access, native support, skill count and best use cases.
Comparison
At a glance
| Dimension | Claude API | Codex |
|---|---|---|
| Vendor | Anthropic | OpenAI |
| Native SKILL.md support | Yes | Yes |
| Verified skills indexed | 13 | 45 |
| Install model | POST /v1/skills | Local folder |
| Shell / Bash access | Sandboxed | Yes |
| Tagline | Claude API + Skills SDK. Pre-built skill_id values plus custom uploads via /v1/skills. | OpenAI's coding agent CLI. Adopted the SKILL.md spec verbatim in Dec 2025. |
Both
9
Skills verified to work on both Claude API and Codex.
Only Claude API
4
Indexed for Claude API but not yet verified on Codex CLI.
Only Codex
36
Indexed for Codex CLI but not yet verified on Claude API.
Verdict
Which should you pick?
Both support SKILL.md natively, so the choice is about ecosystem fit. Pick Claude API for Anthropic integrations and the workflows it makes easiest; pick Codex CLI for OpenAI integrations and its specific surface.
Many teams use both — Skills with the SKILL.md spec are portable, and 9 of the skills indexed here are verified on both agents. Browse the per-agent rankings to see which Skills lead on each platform: Skills for Claude API · Skills for Codex CLI.
FAQ
Common questions
Which is better for SKILL.md skills, Claude API or Codex CLI?
Both support SKILL.md natively. Claude API has 13 verified skills indexed here; Codex CLI has 45. 9 skills work on both.
Can I use the same Skill on Claude API and Codex CLI?
9 of the skills indexed here work on both. The SKILL.md spec is shared, so most skills run cleanly on both — the exceptions are skills that depend on agent-specific tools (Bash, Workflows, MCP patterns).
How do I install a Skill on Claude API?
POST your Skill zip to /v1/skills. You receive a skill_id. Reference it in your messages request — the model loads the Skill on demand.
How do I install a Skill on Codex CLI?
Drop the Skill folder under `~/.codex/skills/` for user-wide or `.codex/skills/` for project-scoped. Codex loads SKILL.md the same way Claude Code does.
Which agent should I pick for cross-platform skill use?
Both support skills natively. Pick by ecosystem fit: Claude API for Anthropic customers, Codex CLI for OpenAI customers.
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