The consensus, in order of how much they write about it mostly: architecture and repo layout, how to test, build commands, dos-and-don'ts, PR etiquette, and code style.
The surprise was tone, and the lack of non-technical constraints.
90% write in must/always/never, and there are 784 explicit "don't" bullets, most of them oddly specific.
It's almost like you can tell exactly which mistake an agent made in each repo.
Some are hilarious: "Do not claim that an interrupted or timed-out test passed" takes the gold for me.
The shortest is 35 words, one rule from Neovim.
> AI Disclosure: If AI was used in any way for a commit, add an AI-assisted: <tool name> trailer to the commit message. If the user commits manually, remind them to add it.
The most popular headings by far were: testing, commands, project overview, and architecture
There's a lot more interesting deets like the average length, nextjs' "Do NOT add "Generated with Claude Code" ..."
Is your AGENTS.md very different to these?