FastMCP should support all of RFC 6570

[ciccolo-anthropic]

Is your feature request related to a problem? Please describe.
The MCP protocol docs state that resource templates are specified according to RFC 6570. But the MCP code uses a regex that rejects some valid URI templates. In particular, it rejects templates with multiple optional params like search://emails{?query,start,end}, which would be useful to have.

Describe the solution you'd like
FastMCP accepts and correctly handles any valid RFC 6570 template.

Describe alternatives you've considered
Optional params can be made mandatory with the tool treating an empty string as if the param was not set. If the full spec is too hard to implement, incrementally supporting it might still be useful.

[dsp-ant]

I think that's totally valid. I am not sure we have the time at the moment to work on it but feel free to send a PR.

[codecracker007]

hey @ciccolo-anthropic yes the full spec of 6570 will indeed be big do you have any priority or preference of the spec in mind on what can be added for now which can be used frequently Since some of the operators and expansions will be a bit annoying to work with when performing reverse matching on the URI template to variable names

@dsp-ant do you guys plan on being full RFC 6570 spec complaint and support multiple levels of template expressions for now its just expansion with no operators right?

[ciccolo-anthropic]

@codecracker007

The specific inciting need I had was for multiple optional params; I honestly don't know 6570 well enough to prioritize beyond that.