# Harness for AI agents

The loop that runs your agent. Take one off the shelf, or skip it and write the loop yourself.

12 options tracked · 10 open source · 8 self-hostable · required

## All options

| Option | What it does | Licence | Self-host | Page |
| --- | --- | --- | --- | --- |
| Claude Code | Anthropic's coding agent — terminal, IDE and SDK, with hooks, skills and MCP built in. | proprietary | no | https://newagent.build/c/claude-code |
| Claude Agent SDK | The Claude Code loop as a library, for agents that are not about code. | proprietary | no | https://newagent.build/c/claude-agent-sdk |
| Hermes Agent | Self-improving agent from Nous Research — writes its own skills from experience and carries them forward. | open source | yes | https://newagent.build/c/hermes-agent |
| OpenClaw | Self-hosted gateway putting an agent in Slack, Telegram, WhatsApp, Signal, Discord and iMessage at once. | open source | yes | https://newagent.build/c/openclaw |
| 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 | https://newagent.build/c/prime-agent |
| 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 | https://newagent.build/c/deepseek-harness |
| OpenAI Agents SDK | Lightweight loop with handoffs, guardrails and sessions. | open source | no | https://newagent.build/c/openai-agents-sdk |
| Codex CLI | OpenAI's terminal coding agent. | open source | no | https://newagent.build/c/codex-cli |
| OpenCode | Open-source terminal coding agent, provider-agnostic. | open source | yes | https://newagent.build/c/opencode |
| Goose | Block's open-source on-machine agent with an extension system. | open source | yes | https://newagent.build/c/goose |
| Letta | Stateful agent server where memory is the primary abstraction. | open source | yes | https://newagent.build/c/letta |
| Roll your own loop | No harness. A while-loop, a model call and your own tool dispatch. | open source | yes | https://newagent.build/c/build-your-own |

## Machine interfaces

- `GET https://newagent.build/api/registry` — every component as JSON
- `GET https://newagent.build/api/vendors` — vendors, with the repo and releases feed to watch
- `GET https://newagent.build/api/advise?q=<plain english>` — recommended stack for a description
- `GET https://newagent.build/api/stack?<layer>=<id>&format=sh|json|md|yml|agents|env` — a stack as files
- `GET https://newagent.build/llms.txt` — the whole registry in one fetch

Any page here also returns markdown if you send `Accept: text/markdown`.