Is OAuth 2.0 required for every MCP server?

No — it's the standard recommendation for remote servers accessed over a network. A purely local stdio server launched by a trusted client (like Claude Desktop) doesn't need its own auth layer, since the client process itself is the trust boundary.

What's the highest-priority item on a production security checklist?

Least-privilege tool scoping and a confirmation step before destructive actions tend to matter most in practice — a server with broad, unscoped permissions is the most common real-world MCP security incident, more so than transport-level issues.

Does audit logging need to capture full tool arguments?

Generally yes, minus any fields that are clearly secrets — you want enough detail to reconstruct what a tool call actually did, which usually means logging arguments and results, not just the tool name and timestamp.