Codex CLI is a harness option for building AI agents. OpenAI's terminal coding agent.
npm install -g @openai/codex
OPENAI_API_KEY=
| Option | What it does | Licence | Self-host |
|---|---|---|---|
| Codex CLI | OpenAI's terminal coding agent. | Open source | No |
| Claude Code | Anthropic's coding agent — terminal, IDE and SDK, with hooks, skills and MCP built in. | Proprietary | No |
| Claude Agent SDK | The Claude Code loop as a library, for agents that are not about code. | Proprietary | No |
| Hermes Agent | Self-improving agent from Nous Research — writes its own skills from experience and carries them forward. | Open source | Yes |
| OpenClaw | Self-hosted gateway putting an agent in Slack, Telegram, WhatsApp, Signal, Discord and iMessage at once. | Open source | Yes |
| Prime Agent | Prime Intellect's recursive-language-model harness — a persistent IPython kernel is the only tool, sub-agents are function calls. | Open source | Yes |
| DeepSeek Harness | Everything is a plugin — the model adapter, the tool registry, the sandbox and the agent loop itself are all swappable. | Open source | Yes |
| OpenAI Agents SDK | Lightweight loop with handoffs, guardrails and sessions. | Open source | No |
| OpenCode | Open-source terminal coding agent, provider-agnostic. | Open source | Yes |
| Goose | Block's open-source on-machine agent with an extension system. | Open source | Yes |
| Letta | Stateful agent server where memory is the primary abstraction. | Open source | Yes |
| Roll your own loop | No harness. A while-loop, a model call and your own tool dispatch. | Open source | Yes |
Every page here answers to Accept: text/markdown and returns the same content at roughly a tenth the tokens. No separate site, no toggle — same URL.
curl -s -H "Accept: text/markdown" https://newagent.build/c/codex-cli