[Microsoft.Extensions.AI] A way to dynamically provide Tools (AIFunctions)

[MihaMarkic]

As far as I looked the docs, one needs a C# method per AIFunction. I'm looking for a way to dynamically provide them - theoretically it should be possible as at the end of the day that metadata gets transformed to JSON, I guess.

I would create metadata required (descriptions, names, argument types ...) and have a single C# method as an entry point.
I'm looking for a solution since my functions aren't known at design time.
At worst I could generate code on the fly, but I'd like to avoid that if possible.

[stephentoub]

You can derive from AIFunction and implement a derived type however you want. AIFunctionFactory.Create is just a convenient way to create an instance that represents a very common case, where you supply a delegate and it creates such a derived instance for you, but that's not the only way they're created. In the ModelContextProtocol library, for example, it has its own AIFunction-derived type that wraps the MCP server's tool information and overrides InvokeAsync to call back to the server.
https://github.com/modelcontextprotocol/csharp-sdk/blob/befa31d5c948f72396a280a675535a653ee19aee/src/ModelContextProtocol.Core/Client/McpClientTool.cs

[MihaMarkic]

Ah, cool, and I'd implement JsonSchema and ReturnJsonSchema for metadata, right?
Is there a builder for these schemas anywhere? Otherwise I'll just craft those myself.

[stephentoub]

Ah, cool, and I'd implement JsonSchema and ReturnJsonSchema for metadata, right?

Yup, plus Name/etc.

Is there a builder for these schemas anywhere?

You can use the helpers in AIJsonUtilities, or use JsonSchemaExporter from System.Text.Json directly (AIJsonUtilities stores on top of it).

[MihaMarkic]

Pity though that some useful functions and types are non public (such as AIJsonUtilities.CreateJsonSchemaCore or AIJsonUtilities.JsonContextNoIndentation)

[stephentoub]

What do you need them for? CreateJsonSchema, for example, wraps CreateJsonSchema ore and just adds in some defaults.

[MihaMarkic]

From what I see, CreateJsonSchemaCore returns a JsonNode which can be added to JsonObject directly (since I'm populating method metadata manually, I use JsonObject as root and then call CreateJsonSchema for each argument and add the result to it). But CreateJsonSchema returns a JsonElement. Which I have to serializa back to JsonNode for it to be added to JsonObject.
Basically, it's an overhead of serializing JsonElement to JsonNode per argument. Not a big deal at the end of the day, just feels unnecessary.