> MCPs are deterministic, SKILLS.md isn't.

MCPs themselves may provide access to tools that are either deterministic or not, but the LLM using them generally isn't deterministic, so when used by an LLM as part of the request-response cycle determinism, if the MCP-provided tool had it, is not in a feature of the overall system.

SKILLS.md relies on a deterministic code execution environment, but has the same issue. I'm not seeing a broad difference in kind here when used in the context of an LLM response generation cycle, and that’s really the only context where both are usable (MCP could be used for non-LLM integration, but that doesn't seem relevant.)