You can learn about them evaluating that site https://github.com/Alexhans/eval-ception and then the pattern should be easy to test on your own thing.
It's agents all the way down!
Submit a GitHub repo containing skills to Tessl, and it will generate the evals, run them, and present the results. https://tessl.io/registry/skills/submit
The evals and results are all shown, no login necessary, so you can assess them yourself. e.g. https://tessl.io/registry/skills/github/coreyhaines31/market... (click details to see the eval texts).
But since it's not, what I do to avoid working on AGENTS.md blind is I test it on whatever causes me to write it.
I have some prompt, the AI messes it up in some way that I think it shouldn't, maybe it's something I've seen it do before and I'm sick of it. So I update AGENTS.md, revert the changes, /undo in the chat context and re-submit the same prompt.