Overview
A harness is the agent runtime that drives the loop — the CLI or service that reads your prompt, calls tools, and edits files. Each one already speaks some model API; the move is always the same: point it at the local proxy at http://127.0.0.1:4356 (Routeplane Cloud is on the Phase D roadmap; not yet shipping) instead of the vendor’s, and address models by their provider/model id. From there the same harness can run on Anthropic, OpenAI, Google, or an open model — with provider selection and fallback underneath.
Harness vs. model source
Section titled “Harness vs. model source”Two of these share a name with a model source, and it’s worth keeping them straight:
| You want to… | Use |
|---|---|
| Run the Claude Code CLI on any model | Claude Code (harness) |
| Spend your Claude plan as tokens | Claude subscription (model) |
| Run the Codex CLI on any model | Codex (harness) |
| Spend your ChatGPT plan as tokens | Codex subscription (model) |
A harness is what runs; a model source is where the tokens come from. You can combine them freely — e.g. drive Claude Code (harness) against your ChatGPT plan (Codex subscription), or against a local Ollama model.
New to Routeplane?
Section titled “New to Routeplane?”Start with the Quick Start to get the proxy running, then come back and point your harness at it.