Thanks for your contribution @ashakirin ! A few comments.

Optional validation

The spec specifically says that tools SHOULD follow the naming conventions (Server > Tools > Tool names). They MAY not follow these, and so we should allow invalid names (although not by default).
We could consider a per-server validator, that you plug in the SyncSpecification and AsyncSpecification. Thoughts?

Client-side validation

I like the approach on the client side, validate but don't fail. The spec itself is super vague, "client can validate" which has no RFC meaning. Maybe we shouldn't even validate on the client side.

If we chose to validate, in the current implementation the log is very verbose if you're writing a client and the server (that you don't control) has an invalid tool name. Every time you make a "call tool request" you get a WARN-level log. I think that's too much, and the level is probably too high. In that case, keep the logs for the "list tool" request but not "call tool".