Optional parameters not working

[rlacaci]

Bug Description
I'm doing simple SDK example in order to learn how to use it for my application. One think that I need and I've not seen in any examples is about optional parameters in a function. I tried to simulate it with string? date

 [McpServerTool, Description("Gets the weather")]
 public string GetWeather([Description("City code")] string cityCode, [Description("Date in yyyy-mm-dd format")] string? date = null)
 {

but when using from MCP Client both parameters appears like required in the function definition.

I've been debugging and investigating a possible solution and the reason seems to be due to default JsonSchemaCreateOptions.RequireAllProperties that is true so regardless of the parameter is or not optional it's always required.

I was able to make it works adding a JsonSchemaCreateOptions in CreateAIFunctionFactoryOptions in AIFunctionMcpServerTool.cs but I'm not familiar with the source code and could be an invalid workaround with side effects (although it works perfectly for me)

 private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
     MethodInfo method, McpServerToolCreateOptions? options) =>
     new()
     {
         Name = options?.Name ?? method.GetCustomAttribute<McpServerToolAttribute>()?.Name,
         Description = options?.Description,
         MarshalResult = static (result, _, cancellationToken) => new ValueTask<object?>(result),
         SerializerOptions = options?.SerializerOptions ?? McpJsonUtilities.DefaultOptions,
         **JsonSchemaCreateOptions=new AIJsonSchemaCreateOptions()
         {
             RequireAllProperties=false
         }**,
     .......

[1357310795]

See #354
you can use McpServerTool.Create to pass AIJsonSchemaCreateOptions now.

although this cannot yet be achieved using the most commonly used WithTool

my workaround is duplicating WithTool/WithToolsFromAssembly into project and apply some minor adjustments

https://github.com/SJTU-Geek/sjtu-mcp-server/blob/a9d8b6ef3f0ff3ea8af229976f0f0b983694bc34/SJTUGeek.MCP.Server/Extensions/McpScriptBuilderExtensions.cs#L55

[jason-lee-x]

That was really helpful!
Thanks a lot.

---

Hoping the WithToolsFromCurrentAssembly can be parts of SDK.

[stephentoub]

cc: @eiriktsarpalis

[1357310795]

Passing AIJsonSchemaCreateOptions into WithTool/WithToolsFromAssembly maybe need a more flexible way.

Perhaps there are more parameters that need to be passed in the future

[eiriktsarpalis]

We recently merged this PR in Microsoft.Extensions.AI that among other things changes the default value of RequireAllProperties to false. The issue should resolve itself once the MCP sdk references an updated version of MEAI.