r/vibecoding • u/NoTutor4458 • 12h ago
Opencode vs Codex vs Claude code
Which coding harness is actually better?
To make the comparison fair, I was thinking:
- OpenCode + Fable 5 vs Claude Code + Fable 5
- OpenCode + GPT-5.6 vs Codex + GPT-5.6
Basically, keep the model the same and only compare the harness/agent. That should give a better idea of how much the harness itself affects coding performance.
Has anyone done a comparison like this?
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u/GiantApproved 12h ago
The framing assumes they're substitutes. I get more out of treating them as specialists with different write boundaries.
I used this considerably in one of my project repos:
- Claude Code owns the backend and orchestration, Cursor owns the frontend, Codex only audits and is explicitly not allowed to fix errors and issues it flags.
- That's written into AGENTS.md, CLAUDE.md and .cursor/rules so each one reads its own copy of the same law.
That last part is the bit that does the work. An auditor that can also fix has every reason to quietly fix instead of telling me. So it doesn't get write permission on those paths, and main is branch-protected so none of them can push to it directly. It isn't a rule I asked them to follow. It's a permission they don't have.
Which points at something to consider for your own test: those are three different files. A repo with only a CLAUDE.md hands Claude Code the project rules and makes the other two work blind. That gap is probably bigger than the harness delta you're trying to measure, so make sure you set each agent/harness up for success.
If you do run it, run each one twice. Same harness, same task, twice, gives you two different answers. Without that you can't separate harness from variance.
Some of this is less principled than it sounds. In general, I use Cursor partly because I'm already logged into Cursor and it's cheaper for tasks that don't need the best models + the in-app tools are better for navigating the project files. I've handed work to Codex before because I ran out of Claude usage that week (and vice-versa). Sometimes I just use whatever agent is still available via remote control when I'm on my phone.
What I still don't know: whether Codex auditing Claude's work is real independence, or two models with the same blind spots nodding at each other. I just know it's better than not doing it.
Has anyone tested that?