Comment by thih9
4 hours ago
How do people build something like a personal harness? Are there tools for that or is it done from scratch?
4 hours ago
How do people build something like a personal harness? Are there tools for that or is it done from scratch?
I like this tutorial for an agent in 50 lines:
http://minimal-agent.com/
And if you add one additional while loop, for user input, you can actually use it! :)
https://gist.github.com/a-n-d-a-i/5461a662ef8a7ee0a5eb7778c8...
Build it from scratch. Understanding fundamentals of how agentic coding harnesses is a must though if you gonna go that route. I think everyone should take time and learn these things, maybe reverse engineer Codex Cli or something like that as a starter. That info is very valuable in this day and age.
Can you say more about Codex? I'm using GPT-5.5 in my own harness and it's not liking it very well, so I'm thinking I ought to make it more Codexy so it's more ergonomic for it. (edit format, tool calls etc.) But haven't gotten around to it yet.
Not the comment author, but I use pi and customize it with my own extensions. Pi automatically tells models how to customize itself, so it's a pretty easy process.
Here is a video I made explaining it from absolute basics:
https://m.youtube.com/watch?v=_AgKuFGvJfI
And the repo:
https://github.com/abtinf/homunctor
I hope you've already invalidated that bearer token :-P
I started mine from scratch in 2023 because I wanted to use LLMs from a terminal and there was nothing else compelling at the time (nowadays there is pi and opencode)
Harnesses are/can be incredibly simple things, not much more than a HTTP client that renders things in a way that suites your taste.
It’s not that difficult, it’s just a system prompt and a set of basic file edit/bash/etc tools.
Me, personally, I didn’t build it from scratch but I ported original CC from published sources into Python and extended it to match my own requirements.
Are you using it with Claude? They only allow their own harness with the subs right? (And per-token billing is like 10x more expensive?)
Building something like this is the todo list of agents.
I found this one easy to understand:
https://ampcode.com/notes/how-to-build-an-agent
The real question is when do you transition from building it with codex/CC to the harness itself.
Lots of ways, it's a good exercise that you will learn a lot doing. Might make you cynical w.r.t. big ai harnesses
I used ADK, Dagger, and a VS Code extension for mine. Currently using opencode though.
Why use a personal harness?
You have to pay API pricing, which is far more costly.
I'd either switch to GLM wholesale or just continue to use Opus within Claude Code as the blessed, subsidized path.
I would guess it is to avoid model lock-in.
My question is still this - why not just use GLM at that point?
The pricing of Opus outside of Claude Code is insane.
The tokens cost too much outside of Anthropic's blessed path.
I use GLM in my custom harness. It completes the same tasks at the same level of quality, except 8x faster and 8x cheaper. (Same goes for GPT!)
I'm not sure how that's possible. I expected to get increased correctness for that order of magnitude (something something test-time compute!) but I am not getting it.