Skills are just markdown files in a folder that any agent that can read files can figure out.

Just tell your non-Claude agent to read your skills directory, and extract the preambles.

They are just text files though. I'm sensitive to vendor lock-in and do not perceive a standard folder structure and bare text files to be that.

It's definitely not vendor locked. For instance, I have made it work with Gemini with Open-Skills[1].

It is after all a collection of instructions and code that any other llm can read and understand and then do a code execution (via tool call / mcp call)

1. Open-Skills: https://github.com/BandarLabs/open-skills